DWARF: Never emit (0, 0) to mean an empty span in debug_loc (#2940)

After mapping to the new positions, and after relativizing to the
base, if we end up with (0, 0) then we must emit something else, as
that would be interpreted as the end of a list. As it is an empty
span, the actual value doesn't matter, it just has to be != 0.
This can happen if the very first span in a compile unit is an
empty span, in which case relative to the base of the compile unit
we would have (0, 0).

4 files changed, 733 insertions, 0 deletions

diff --git a/src/wasm/wasm-debug.cpp b/src/wasm/wasm-debug.cpp
index e90dc6d48..112c805d8 100644
--- a/src/wasm/wasm-debug.cpp
+++ b/src/wasm/wasm-debug.cpp
@@ -1001,6 +1001,16 @@ static void updateLoc(llvm::DWARFYAML::Data& yaml,
         assert(newStart >= newBase && newEnd >= newBase);
         newStart -= newBase;
         newEnd -= newBase;
+        if (newStart == 0 && newEnd == 0) {
+          // After mapping to the new positions, and after relativizing to the
+          // base, if we end up with (0, 0) then we must emit something else, as
+          // that would be interpreted as the end of a list. As it is an empty
+          // span, the actual value doesn't matter, it just has to be != 0.
+          // This can happen if the very first span in a compile unit is an
+          // empty span, in which case relative to the base of the compile unit
+          // we would have (0, 0).
+          newStart = newEnd = IGNOREABLE_LOCATION;
+        }
       }
       // The loc start and end markers have been preserved. However, TODO
       // instructions in the middle may have moved around, making the loc no
diff --git a/test/passes/fib2_emptylocspan.bin.txt b/test/passes/fib2_emptylocspan.bin.txt
new file mode 100644
index 000000000..7c9449300
--- /dev/null
+++ b/test/passes/fib2_emptylocspan.bin.txt
@@ -0,0 +1,722 @@
+DWARF debug info
+================
+
+Contains section .debug_info (168 bytes)
+Contains section .debug_loc (143 bytes)
+Contains section .debug_ranges (24 bytes)
+Contains section .debug_abbrev (131 bytes)
+Contains section .debug_line (106 bytes)
+Contains section .debug_str (180 bytes)
+
+.debug_abbrev contents:
+Abbrev table for offset: 0x00000000
+[1] DW_TAG_compile_unit	DW_CHILDREN_yes
+	DW_AT_producer	DW_FORM_strp
+	DW_AT_language	DW_FORM_data2
+	DW_AT_name	DW_FORM_strp
+	DW_AT_stmt_list	DW_FORM_sec_offset
+	DW_AT_comp_dir	DW_FORM_strp
+	DW_AT_low_pc	DW_FORM_addr
+	DW_AT_ranges	DW_FORM_sec_offset
+
+[2] DW_TAG_subprogram	DW_CHILDREN_yes
+	DW_AT_low_pc	DW_FORM_addr
+	DW_AT_high_pc	DW_FORM_data4
+	DW_AT_frame_base	DW_FORM_exprloc
+	DW_AT_GNU_all_call_sites	DW_FORM_flag_present
+	DW_AT_name	DW_FORM_strp
+	DW_AT_decl_file	DW_FORM_data1
+	DW_AT_decl_line	DW_FORM_data1
+	DW_AT_prototyped	DW_FORM_flag_present
+	DW_AT_type	DW_FORM_ref4
+	DW_AT_external	DW_FORM_flag_present
+
+[3] DW_TAG_formal_parameter	DW_CHILDREN_no
+	DW_AT_name	DW_FORM_strp
+	DW_AT_decl_file	DW_FORM_data1
+	DW_AT_decl_line	DW_FORM_data1
+	DW_AT_type	DW_FORM_ref4
+
+[4] DW_TAG_variable	DW_CHILDREN_no
+	DW_AT_location	DW_FORM_sec_offset
+	DW_AT_name	DW_FORM_strp
+	DW_AT_decl_file	DW_FORM_data1
+	DW_AT_decl_line	DW_FORM_data1
+	DW_AT_type	DW_FORM_ref4
+
+[5] DW_TAG_variable	DW_CHILDREN_no
+	DW_AT_name	DW_FORM_strp
+	DW_AT_decl_file	DW_FORM_data1
+	DW_AT_decl_line	DW_FORM_data1
+	DW_AT_type	DW_FORM_ref4
+
+[6] DW_TAG_subprogram	DW_CHILDREN_yes
+	DW_AT_low_pc	DW_FORM_addr
+	DW_AT_high_pc	DW_FORM_data4
+	DW_AT_frame_base	DW_FORM_exprloc
+	DW_AT_GNU_all_call_sites	DW_FORM_flag_present
+	DW_AT_name	DW_FORM_strp
+	DW_AT_decl_file	DW_FORM_data1
+	DW_AT_decl_line	DW_FORM_data1
+	DW_AT_type	DW_FORM_ref4
+	DW_AT_external	DW_FORM_flag_present
+
+[7] DW_TAG_GNU_call_site	DW_CHILDREN_no
+	DW_AT_low_pc	DW_FORM_addr
+
+[8] DW_TAG_base_type	DW_CHILDREN_no
+	DW_AT_name	DW_FORM_strp
+	DW_AT_encoding	DW_FORM_data1
+	DW_AT_byte_size	DW_FORM_data1
+
+
+.debug_info contents:
+0x00000000: Compile Unit: length = 0x000000a4 version = 0x0004 abbr_offset = 0x0000 addr_size = 0x04 (next unit at 0x000000a8)
+
+0x0000000b: DW_TAG_compile_unit [1] *
+              DW_AT_producer [DW_FORM_strp]	( .debug_str[0x00000000] = "clang version 11.0.0 (https://github.com/llvm/llvm-project.git 313d89724ce3ccf66c1c51849903e1e6d184dd85)")
+              DW_AT_language [DW_FORM_data2]	(DW_LANG_C99)
+              DW_AT_name [DW_FORM_strp]	( .debug_str[0x00000069] = "fib2.c")
+              DW_AT_stmt_list [DW_FORM_sec_offset]	(0x00000000)
+              DW_AT_comp_dir [DW_FORM_strp]	( .debug_str[0x00000070] = "/usr/local/google/home/azakai/Dev/2-binaryen")
+              DW_AT_low_pc [DW_FORM_addr]	(0x0000000000000000)
+              DW_AT_ranges [DW_FORM_sec_offset]	(0x00000000
+                 [0x00000005, 0x0000003d)
+                 [0x0000003e, 0x00000048))
+
+0x00000026:   DW_TAG_subprogram [2] *
+                DW_AT_low_pc [DW_FORM_addr]	(0x0000000000000005)
+                DW_AT_high_pc [DW_FORM_data4]	(0x00000038)
+                DW_AT_frame_base [DW_FORM_exprloc]	(DW_OP_WASM_location 0x1 +0, DW_OP_stack_value)
+                DW_AT_GNU_all_call_sites [DW_FORM_flag_present]	(true)
+                DW_AT_name [DW_FORM_strp]	( .debug_str[0x0000009d] = "fib")
+                DW_AT_decl_file [DW_FORM_data1]	("/usr/local/google/home/azakai/Dev/2-binaryen/fib2.c")
+                DW_AT_decl_line [DW_FORM_data1]	(1)
+                DW_AT_prototyped [DW_FORM_flag_present]	(true)
+                DW_AT_type [DW_FORM_ref4]	(cu + 0x00a0 => {0x000000a0} "int")
+                DW_AT_external [DW_FORM_flag_present]	(true)
+
+0x0000003e:     DW_TAG_formal_parameter [3]  
+                  DW_AT_name [DW_FORM_strp]	( .debug_str[0x000000aa] = "n")
+                  DW_AT_decl_file [DW_FORM_data1]	("/usr/local/google/home/azakai/Dev/2-binaryen/fib2.c")
+                  DW_AT_decl_line [DW_FORM_data1]	(1)
+                  DW_AT_type [DW_FORM_ref4]	(cu + 0x00a0 => {0x000000a0} "int")
+
+0x00000049:     DW_TAG_variable [4]  
+                  DW_AT_location [DW_FORM_sec_offset]	(0x00000000: 
+                     [0xffffffff,  0x00000005): 
+                     [0x00000007,  0x00000007): DW_OP_consts +0, DW_OP_stack_value
+                     [0x0000001e,  0x0000001e): DW_OP_WASM_location 0x0 +4, DW_OP_stack_value)
+                  DW_AT_name [DW_FORM_strp]	( .debug_str[0x000000ac] = "a")
+                  DW_AT_decl_file [DW_FORM_data1]	("/usr/local/google/home/azakai/Dev/2-binaryen/fib2.c")
+                  DW_AT_decl_line [DW_FORM_data1]	(2)
+                  DW_AT_type [DW_FORM_ref4]	(cu + 0x00a0 => {0x000000a0} "int")
+
+0x00000058:     DW_TAG_variable [4]  
+                  DW_AT_location [DW_FORM_sec_offset]	(0x0000002b: 
+                     [0xffffffff,  0x00000005): 
+                     [0x00000007,  0x00000010): DW_OP_consts +1, DW_OP_stack_value
+                     [0x0000001e,  0x00000023): DW_OP_WASM_location 0x0 +4, DW_OP_stack_value
+                     [0x00000023,  0x00000033): DW_OP_WASM_location 0x0 +1, DW_OP_stack_value)
+                  DW_AT_name [DW_FORM_strp]	( .debug_str[0x000000ae] = "b")
+                  DW_AT_decl_file [DW_FORM_data1]	("/usr/local/google/home/azakai/Dev/2-binaryen/fib2.c")
+                  DW_AT_decl_line [DW_FORM_data1]	(2)
+                  DW_AT_type [DW_FORM_ref4]	(cu + 0x00a0 => {0x000000a0} "int")
+
+0x00000067:     DW_TAG_variable [4]  
+                  DW_AT_location [DW_FORM_sec_offset]	(0x00000064: 
+                     [0xffffffff,  0x00000005): 
+                     [0x00000007,  0x00000010): DW_OP_consts +0, DW_OP_stack_value
+                     [0x0000002e,  0x00000033): DW_OP_WASM_location 0x0 +3, DW_OP_stack_value)
+                  DW_AT_name [DW_FORM_strp]	( .debug_str[0x000000b0] = "i")
+                  DW_AT_decl_file [DW_FORM_data1]	("/usr/local/google/home/azakai/Dev/2-binaryen/fib2.c")
+                  DW_AT_decl_line [DW_FORM_data1]	(2)
+                  DW_AT_type [DW_FORM_ref4]	(cu + 0x00a0 => {0x000000a0} "int")
+
+0x00000076:     DW_TAG_variable [5]  
+                  DW_AT_name [DW_FORM_strp]	( .debug_str[0x000000b2] = "t")
+                  DW_AT_decl_file [DW_FORM_data1]	("/usr/local/google/home/azakai/Dev/2-binaryen/fib2.c")
+                  DW_AT_decl_line [DW_FORM_data1]	(2)
+                  DW_AT_type [DW_FORM_ref4]	(cu + 0x00a0 => {0x000000a0} "int")
+
+0x00000081:     NULL
+
+0x00000082:   DW_TAG_subprogram [6] *
+                DW_AT_low_pc [DW_FORM_addr]	(0x000000000000003e)
+                DW_AT_high_pc [DW_FORM_data4]	(0x0000000a)
+                DW_AT_frame_base [DW_FORM_exprloc]	(DW_OP_WASM_location 0x1 +0, DW_OP_stack_value)
+                DW_AT_GNU_all_call_sites [DW_FORM_flag_present]	(true)
+                DW_AT_name [DW_FORM_strp]	( .debug_str[0x000000a5] = "main")
+                DW_AT_decl_file [DW_FORM_data1]	("/usr/local/google/home/azakai/Dev/2-binaryen/fib2.c")
+                DW_AT_decl_line [DW_FORM_data1]	(11)
+                DW_AT_type [DW_FORM_ref4]	(cu + 0x00a0 => {0x000000a0} "int")
+                DW_AT_external [DW_FORM_flag_present]	(true)
+
+0x0000009a:     DW_TAG_GNU_call_site [7]  
+                  DW_AT_low_pc [DW_FORM_addr]	(0x0000000000000047)
+
+0x0000009f:     NULL
+
+0x000000a0:   DW_TAG_base_type [8]  
+                DW_AT_name [DW_FORM_strp]	( .debug_str[0x000000a1] = "int")
+                DW_AT_encoding [DW_FORM_data1]	(DW_ATE_signed)
+                DW_AT_byte_size [DW_FORM_data1]	(0x04)
+
+0x000000a7:   NULL
+
+.debug_loc contents:
+0x00000000: 
+            [0xffffffff,  0x00000005): 
+            [0x00000007,  0x00000007): DW_OP_consts +0, DW_OP_stack_value
+            [0x0000001e,  0x0000001e): DW_OP_WASM_location 0x0 +4, DW_OP_stack_value
+
+0x0000002b: 
+            [0xffffffff,  0x00000005): 
+            [0x00000007,  0x00000010): DW_OP_consts +1, DW_OP_stack_value
+            [0x0000001e,  0x00000023): DW_OP_WASM_location 0x0 +4, DW_OP_stack_value
+            [0x00000023,  0x00000033): DW_OP_WASM_location 0x0 +1, DW_OP_stack_value
+
+0x00000064: 
+            [0xffffffff,  0x00000005): 
+            [0x00000007,  0x00000010): DW_OP_consts +0, DW_OP_stack_value
+            [0x0000002e,  0x00000033): DW_OP_WASM_location 0x0 +3, DW_OP_stack_value
+
+.debug_line contents:
+debug_line[0x00000000]
+Line table prologue:
+    total_length: 0x00000066
+         version: 4
+ prologue_length: 0x0000001e
+ min_inst_length: 1
+max_ops_per_inst: 1
+ default_is_stmt: 1
+       line_base: -5
+      line_range: 14
+     opcode_base: 13
+standard_opcode_lengths[DW_LNS_copy] = 0
+standard_opcode_lengths[DW_LNS_advance_pc] = 1
+standard_opcode_lengths[DW_LNS_advance_line] = 1
+standard_opcode_lengths[DW_LNS_set_file] = 1
+standard_opcode_lengths[DW_LNS_set_column] = 1
+standard_opcode_lengths[DW_LNS_negate_stmt] = 0
+standard_opcode_lengths[DW_LNS_set_basic_block] = 0
+standard_opcode_lengths[DW_LNS_const_add_pc] = 0
+standard_opcode_lengths[DW_LNS_fixed_advance_pc] = 1
+standard_opcode_lengths[DW_LNS_set_prologue_end] = 0
+standard_opcode_lengths[DW_LNS_set_epilogue_begin] = 0
+standard_opcode_lengths[DW_LNS_set_isa] = 1
+file_names[  1]:
+           name: "fib2.c"
+      dir_index: 0
+       mod_time: 0x00000000
+         length: 0x00000000
+0x00000028: 00 DW_LNE_set_address (0x0000000000000005)
+0x0000002f: 01 DW_LNS_copy
+            0x0000000000000005      1      0      1   0             0  is_stmt
+
+
+0x00000030: 05 DW_LNS_set_column (17)
+0x00000032: 0a DW_LNS_set_prologue_end
+0x00000033: 92 address += 9,  line += 2
+            0x000000000000000e      3     17      1   0             0  is_stmt prologue_end
+
+0x00000034: 05 DW_LNS_set_column (3)
+0x00000036: 06 DW_LNS_negate_stmt
+0x00000037: 58 address += 5,  line += 0
+            0x0000000000000013      3      3      1   0             0 
+
+0x00000038: 2b address += 2,  line += -3
+            0x0000000000000015      0      3      1   0             0 
+
+0x00000039: 05 DW_LNS_set_column (7)
+0x0000003b: 06 DW_LNS_negate_stmt
+0x0000003c: c0 address += 12,  line += 6
+            0x0000000000000021      6      7      1   0             0  is_stmt
+
+0x0000003d: 06 DW_LNS_negate_stmt
+0x0000003e: 03 DW_LNS_advance_line (0)
+0x00000040: 74 address += 7,  line += 0
+            0x0000000000000028      0      7      1   0             0 
+
+0x00000041: 05 DW_LNS_set_column (23)
+0x00000043: 06 DW_LNS_negate_stmt
+0x00000044: 4d address += 4,  line += 3
+            0x000000000000002c      3     23      1   0             0  is_stmt
+
+0x00000045: 05 DW_LNS_set_column (17)
+0x00000047: 06 DW_LNS_negate_stmt
+0x00000048: 58 address += 5,  line += 0
+            0x0000000000000031      3     17      1   0             0 
+
+0x00000049: 05 DW_LNS_set_column (3)
+0x0000004b: 58 address += 5,  line += 0
+            0x0000000000000036      3      3      1   0             0 
+
+0x0000004c: 06 DW_LNS_negate_stmt
+0x0000004d: 4f address += 4,  line += 5
+            0x000000000000003a      8      3      1   0             0  is_stmt
+
+0x0000004e: 02 DW_LNS_advance_pc (3)
+0x00000050: 00 DW_LNE_end_sequence
+            0x000000000000003d      8      3      1   0             0  is_stmt end_sequence
+
+0x00000053: 00 DW_LNE_set_address (0x000000000000003e)
+0x0000005a: 03 DW_LNS_advance_line (11)
+0x0000005c: 01 DW_LNS_copy
+            0x000000000000003e     11      0      1   0             0  is_stmt
+
+
+0x0000005d: 05 DW_LNS_set_column (10)
+0x0000005f: 0a DW_LNS_set_prologue_end
+0x00000060: 3d address += 3,  line += 1
+            0x0000000000000041     12     10      1   0             0  is_stmt prologue_end
+
+0x00000061: 05 DW_LNS_set_column (3)
+0x00000063: 06 DW_LNS_negate_stmt
+0x00000064: 66 address += 6,  line += 0
+            0x0000000000000047     12      3      1   0             0 
+
+0x00000065: 02 DW_LNS_advance_pc (1)
+0x00000067: 00 DW_LNE_end_sequence
+            0x0000000000000048     12      3      1   0             0  end_sequence
+
+
+.debug_str contents:
+0x00000000: "clang version 11.0.0 (https://github.com/llvm/llvm-project.git 313d89724ce3ccf66c1c51849903e1e6d184dd85)"
+0x00000069: "fib2.c"
+0x00000070: "/usr/local/google/home/azakai/Dev/2-binaryen"
+0x0000009d: "fib"
+0x000000a1: "int"
+0x000000a5: "main"
+0x000000aa: "n"
+0x000000ac: "a"
+0x000000ae: "b"
+0x000000b0: "i"
+0x000000b2: "t"
+
+.debug_ranges contents:
+00000000 00000005 0000003d
+00000000 0000003e 00000048
+00000000 <End of list>
+DWARF debug info
+================
+
+Contains section .debug_info (168 bytes)
+Contains section .debug_loc (143 bytes)
+Contains section .debug_ranges (24 bytes)
+Contains section .debug_abbrev (131 bytes)
+Contains section .debug_line (183 bytes)
+Contains section .debug_str (180 bytes)
+
+.debug_abbrev contents:
+Abbrev table for offset: 0x00000000
+[1] DW_TAG_compile_unit	DW_CHILDREN_yes
+	DW_AT_producer	DW_FORM_strp
+	DW_AT_language	DW_FORM_data2
+	DW_AT_name	DW_FORM_strp
+	DW_AT_stmt_list	DW_FORM_sec_offset
+	DW_AT_comp_dir	DW_FORM_strp
+	DW_AT_low_pc	DW_FORM_addr
+	DW_AT_ranges	DW_FORM_sec_offset
+
+[2] DW_TAG_subprogram	DW_CHILDREN_yes
+	DW_AT_low_pc	DW_FORM_addr
+	DW_AT_high_pc	DW_FORM_data4
+	DW_AT_frame_base	DW_FORM_exprloc
+	DW_AT_GNU_all_call_sites	DW_FORM_flag_present
+	DW_AT_name	DW_FORM_strp
+	DW_AT_decl_file	DW_FORM_data1
+	DW_AT_decl_line	DW_FORM_data1
+	DW_AT_prototyped	DW_FORM_flag_present
+	DW_AT_type	DW_FORM_ref4
+	DW_AT_external	DW_FORM_flag_present
+
+[3] DW_TAG_formal_parameter	DW_CHILDREN_no
+	DW_AT_name	DW_FORM_strp
+	DW_AT_decl_file	DW_FORM_data1
+	DW_AT_decl_line	DW_FORM_data1
+	DW_AT_type	DW_FORM_ref4
+
+[4] DW_TAG_variable	DW_CHILDREN_no
+	DW_AT_location	DW_FORM_sec_offset
+	DW_AT_name	DW_FORM_strp
+	DW_AT_decl_file	DW_FORM_data1
+	DW_AT_decl_line	DW_FORM_data1
+	DW_AT_type	DW_FORM_ref4
+
+[5] DW_TAG_variable	DW_CHILDREN_no
+	DW_AT_name	DW_FORM_strp
+	DW_AT_decl_file	DW_FORM_data1
+	DW_AT_decl_line	DW_FORM_data1
+	DW_AT_type	DW_FORM_ref4
+
+[6] DW_TAG_subprogram	DW_CHILDREN_yes
+	DW_AT_low_pc	DW_FORM_addr
+	DW_AT_high_pc	DW_FORM_data4
+	DW_AT_frame_base	DW_FORM_exprloc
+	DW_AT_GNU_all_call_sites	DW_FORM_flag_present
+	DW_AT_name	DW_FORM_strp
+	DW_AT_decl_file	DW_FORM_data1
+	DW_AT_decl_line	DW_FORM_data1
+	DW_AT_type	DW_FORM_ref4
+	DW_AT_external	DW_FORM_flag_present
+
+[7] DW_TAG_GNU_call_site	DW_CHILDREN_no
+	DW_AT_low_pc	DW_FORM_addr
+
+[8] DW_TAG_base_type	DW_CHILDREN_no
+	DW_AT_name	DW_FORM_strp
+	DW_AT_encoding	DW_FORM_data1
+	DW_AT_byte_size	DW_FORM_data1
+
+
+.debug_info contents:
+0x00000000: Compile Unit: length = 0x000000a4 version = 0x0004 abbr_offset = 0x0000 addr_size = 0x04 (next unit at 0x000000a8)
+
+0x0000000b: DW_TAG_compile_unit [1] *
+              DW_AT_producer [DW_FORM_strp]	( .debug_str[0x00000000] = "clang version 11.0.0 (https://github.com/llvm/llvm-project.git 313d89724ce3ccf66c1c51849903e1e6d184dd85)")
+              DW_AT_language [DW_FORM_data2]	(DW_LANG_C99)
+              DW_AT_name [DW_FORM_strp]	( .debug_str[0x00000069] = "fib2.c")
+              DW_AT_stmt_list [DW_FORM_sec_offset]	(0x00000000)
+              DW_AT_comp_dir [DW_FORM_strp]	( .debug_str[0x00000070] = "/usr/local/google/home/azakai/Dev/2-binaryen")
+              DW_AT_low_pc [DW_FORM_addr]	(0x0000000000000000)
+              DW_AT_ranges [DW_FORM_sec_offset]	(0x00000000
+                 [0x00000005, 0x0000003d)
+                 [0x0000003e, 0x00000044))
+
+0x00000026:   DW_TAG_subprogram [2] *
+                DW_AT_low_pc [DW_FORM_addr]	(0x0000000000000005)
+                DW_AT_high_pc [DW_FORM_data4]	(0x00000038)
+                DW_AT_frame_base [DW_FORM_exprloc]	(DW_OP_WASM_location 0x1 +0, DW_OP_stack_value)
+                DW_AT_GNU_all_call_sites [DW_FORM_flag_present]	(true)
+                DW_AT_name [DW_FORM_strp]	( .debug_str[0x0000009d] = "fib")
+                DW_AT_decl_file [DW_FORM_data1]	("/usr/local/google/home/azakai/Dev/2-binaryen/fib2.c")
+                DW_AT_decl_line [DW_FORM_data1]	(1)
+                DW_AT_prototyped [DW_FORM_flag_present]	(true)
+                DW_AT_type [DW_FORM_ref4]	(cu + 0x00a0 => {0x000000a0} "int")
+                DW_AT_external [DW_FORM_flag_present]	(true)
+
+0x0000003e:     DW_TAG_formal_parameter [3]  
+                  DW_AT_name [DW_FORM_strp]	( .debug_str[0x000000aa] = "n")
+                  DW_AT_decl_file [DW_FORM_data1]	("/usr/local/google/home/azakai/Dev/2-binaryen/fib2.c")
+                  DW_AT_decl_line [DW_FORM_data1]	(1)
+                  DW_AT_type [DW_FORM_ref4]	(cu + 0x00a0 => {0x000000a0} "int")
+
+0x00000049:     DW_TAG_variable [4]  
+                  DW_AT_location [DW_FORM_sec_offset]	(0x00000000: 
+                     [0xffffffff,  0x0000000c): 
+                     [0x00000001,  0x00000001): DW_OP_consts +0, DW_OP_stack_value
+                     [0x00000017,  0x00000017): DW_OP_WASM_location 0x0 +4, DW_OP_stack_value)
+                  DW_AT_name [DW_FORM_strp]	( .debug_str[0x000000ac] = "a")
+                  DW_AT_decl_file [DW_FORM_data1]	("/usr/local/google/home/azakai/Dev/2-binaryen/fib2.c")
+                  DW_AT_decl_line [DW_FORM_data1]	(2)
+                  DW_AT_type [DW_FORM_ref4]	(cu + 0x00a0 => {0x000000a0} "int")
+
+0x00000058:     DW_TAG_variable [4]  
+                  DW_AT_location [DW_FORM_sec_offset]	(0x0000002b: 
+                     [0xffffffff,  0x0000000c): 
+                     [0x00000000,  0x00000009): DW_OP_consts +1, DW_OP_stack_value
+                     [0x00000017,  0x0000001c): DW_OP_WASM_location 0x0 +4, DW_OP_stack_value
+                     [0x0000001c,  0x0000002c): DW_OP_WASM_location 0x0 +1, DW_OP_stack_value)
+                  DW_AT_name [DW_FORM_strp]	( .debug_str[0x000000ae] = "b")
+                  DW_AT_decl_file [DW_FORM_data1]	("/usr/local/google/home/azakai/Dev/2-binaryen/fib2.c")
+                  DW_AT_decl_line [DW_FORM_data1]	(2)
+                  DW_AT_type [DW_FORM_ref4]	(cu + 0x00a0 => {0x000000a0} "int")
+
+0x00000067:     DW_TAG_variable [4]  
+                  DW_AT_location [DW_FORM_sec_offset]	(0x00000064: 
+                     [0xffffffff,  0x0000000c): 
+                     [0x00000000,  0x00000009): DW_OP_consts +0, DW_OP_stack_value
+                     [0x00000027,  0x0000002c): DW_OP_WASM_location 0x0 +3, DW_OP_stack_value)
+                  DW_AT_name [DW_FORM_strp]	( .debug_str[0x000000b0] = "i")
+                  DW_AT_decl_file [DW_FORM_data1]	("/usr/local/google/home/azakai/Dev/2-binaryen/fib2.c")
+                  DW_AT_decl_line [DW_FORM_data1]	(2)
+                  DW_AT_type [DW_FORM_ref4]	(cu + 0x00a0 => {0x000000a0} "int")
+
+0x00000076:     DW_TAG_variable [5]  
+                  DW_AT_name [DW_FORM_strp]	( .debug_str[0x000000b2] = "t")
+                  DW_AT_decl_file [DW_FORM_data1]	("/usr/local/google/home/azakai/Dev/2-binaryen/fib2.c")
+                  DW_AT_decl_line [DW_FORM_data1]	(2)
+                  DW_AT_type [DW_FORM_ref4]	(cu + 0x00a0 => {0x000000a0} "int")
+
+0x00000081:     NULL
+
+0x00000082:   DW_TAG_subprogram [6] *
+                DW_AT_low_pc [DW_FORM_addr]	(0x000000000000003e)
+                DW_AT_high_pc [DW_FORM_data4]	(0x00000006)
+                DW_AT_frame_base [DW_FORM_exprloc]	(DW_OP_WASM_location 0x1 +0, DW_OP_stack_value)
+                DW_AT_GNU_all_call_sites [DW_FORM_flag_present]	(true)
+                DW_AT_name [DW_FORM_strp]	( .debug_str[0x000000a5] = "main")
+                DW_AT_decl_file [DW_FORM_data1]	("/usr/local/google/home/azakai/Dev/2-binaryen/fib2.c")
+                DW_AT_decl_line [DW_FORM_data1]	(11)
+                DW_AT_type [DW_FORM_ref4]	(cu + 0x00a0 => {0x000000a0} "int")
+                DW_AT_external [DW_FORM_flag_present]	(true)
+
+0x0000009a:     DW_TAG_GNU_call_site [7]  
+                  DW_AT_low_pc [DW_FORM_addr]	(0x0000000000000000)
+
+0x0000009f:     NULL
+
+0x000000a0:   DW_TAG_base_type [8]  
+                DW_AT_name [DW_FORM_strp]	( .debug_str[0x000000a1] = "int")
+                DW_AT_encoding [DW_FORM_data1]	(DW_ATE_signed)
+                DW_AT_byte_size [DW_FORM_data1]	(0x04)
+
+0x000000a7:   NULL
+
+.debug_loc contents:
+0x00000000: 
+            [0xffffffff,  0x0000000c): 
+            [0x00000001,  0x00000001): DW_OP_consts +0, DW_OP_stack_value
+            [0x00000017,  0x00000017): DW_OP_WASM_location 0x0 +4, DW_OP_stack_value
+
+0x0000002b: 
+            [0xffffffff,  0x0000000c): 
+            [0x00000000,  0x00000009): DW_OP_consts +1, DW_OP_stack_value
+            [0x00000017,  0x0000001c): DW_OP_WASM_location 0x0 +4, DW_OP_stack_value
+            [0x0000001c,  0x0000002c): DW_OP_WASM_location 0x0 +1, DW_OP_stack_value
+
+0x00000064: 
+            [0xffffffff,  0x0000000c): 
+            [0x00000000,  0x00000009): DW_OP_consts +0, DW_OP_stack_value
+            [0x00000027,  0x0000002c): DW_OP_WASM_location 0x0 +3, DW_OP_stack_value
+
+.debug_line contents:
+debug_line[0x00000000]
+Line table prologue:
+    total_length: 0x000000b3
+         version: 4
+ prologue_length: 0x0000001e
+ min_inst_length: 1
+max_ops_per_inst: 1
+ default_is_stmt: 1
+       line_base: -5
+      line_range: 14
+     opcode_base: 13
+standard_opcode_lengths[DW_LNS_copy] = 0
+standard_opcode_lengths[DW_LNS_advance_pc] = 1
+standard_opcode_lengths[DW_LNS_advance_line] = 1
+standard_opcode_lengths[DW_LNS_set_file] = 1
+standard_opcode_lengths[DW_LNS_set_column] = 1
+standard_opcode_lengths[DW_LNS_negate_stmt] = 0
+standard_opcode_lengths[DW_LNS_set_basic_block] = 0
+standard_opcode_lengths[DW_LNS_const_add_pc] = 0
+standard_opcode_lengths[DW_LNS_fixed_advance_pc] = 1
+standard_opcode_lengths[DW_LNS_set_prologue_end] = 0
+standard_opcode_lengths[DW_LNS_set_epilogue_begin] = 0
+standard_opcode_lengths[DW_LNS_set_isa] = 1
+file_names[  1]:
+           name: "fib2.c"
+      dir_index: 0
+       mod_time: 0x00000000
+         length: 0x00000000
+0x00000028: 00 DW_LNE_set_address (0x0000000000000005)
+0x0000002f: 01 DW_LNS_copy
+            0x0000000000000005      1      0      1   0             0  is_stmt
+
+
+0x00000030: 00 DW_LNE_set_address (0x000000000000000e)
+0x00000037: 03 DW_LNS_advance_line (3)
+0x00000039: 05 DW_LNS_set_column (17)
+0x0000003b: 0a DW_LNS_set_prologue_end
+0x0000003c: 01 DW_LNS_copy
+            0x000000000000000e      3     17      1   0             0  is_stmt prologue_end
+
+
+0x0000003d: 00 DW_LNE_set_address (0x0000000000000013)
+0x00000044: 05 DW_LNS_set_column (3)
+0x00000046: 06 DW_LNS_negate_stmt
+0x00000047: 01 DW_LNS_copy
+            0x0000000000000013      3      3      1   0             0 
+
+
+0x00000048: 00 DW_LNE_set_address (0x0000000000000021)
+0x0000004f: 03 DW_LNS_advance_line (6)
+0x00000051: 05 DW_LNS_set_column (7)
+0x00000053: 06 DW_LNS_negate_stmt
+0x00000054: 01 DW_LNS_copy
+            0x0000000000000021      6      7      1   0             0  is_stmt
+
+
+0x00000055: 00 DW_LNE_set_address (0x000000000000002c)
+0x0000005c: 03 DW_LNS_advance_line (3)
+0x0000005e: 05 DW_LNS_set_column (23)
+0x00000060: 01 DW_LNS_copy
+            0x000000000000002c      3     23      1   0             0  is_stmt
+
+
+0x00000061: 00 DW_LNE_set_address (0x0000000000000031)
+0x00000068: 05 DW_LNS_set_column (17)
+0x0000006a: 06 DW_LNS_negate_stmt
+0x0000006b: 01 DW_LNS_copy
+            0x0000000000000031      3     17      1   0             0 
+
+
+0x0000006c: 00 DW_LNE_set_address (0x0000000000000036)
+0x00000073: 05 DW_LNS_set_column (3)
+0x00000075: 01 DW_LNS_copy
+            0x0000000000000036      3      3      1   0             0 
+
+
+0x00000076: 00 DW_LNE_set_address (0x000000000000003a)
+0x0000007d: 03 DW_LNS_advance_line (8)
+0x0000007f: 06 DW_LNS_negate_stmt
+0x00000080: 01 DW_LNS_copy
+            0x000000000000003a      8      3      1   0             0  is_stmt
+
+
+0x00000081: 00 DW_LNE_set_address (0x000000000000003d)
+0x00000088: 00 DW_LNE_end_sequence
+            0x000000000000003d      8      3      1   0             0  is_stmt end_sequence
+
+0x0000008b: 00 DW_LNE_set_address (0x000000000000003e)
+0x00000092: 03 DW_LNS_advance_line (11)
+0x00000094: 01 DW_LNS_copy
+            0x000000000000003e     11      0      1   0             0  is_stmt
+
+
+0x00000095: 00 DW_LNE_set_address (0x0000000000000041)
+0x0000009c: 03 DW_LNS_advance_line (12)
+0x0000009e: 05 DW_LNS_set_column (10)
+0x000000a0: 0a DW_LNS_set_prologue_end
+0x000000a1: 01 DW_LNS_copy
+            0x0000000000000041     12     10      1   0             0  is_stmt prologue_end
+
+
+0x000000a2: 00 DW_LNE_set_address (0x0000000000000043)
+0x000000a9: 05 DW_LNS_set_column (3)
+0x000000ab: 06 DW_LNS_negate_stmt
+0x000000ac: 01 DW_LNS_copy
+            0x0000000000000043     12      3      1   0             0 
+
+
+0x000000ad: 00 DW_LNE_set_address (0x0000000000000044)
+0x000000b4: 00 DW_LNE_end_sequence
+            0x0000000000000044     12      3      1   0             0  end_sequence
+
+
+.debug_str contents:
+0x00000000: "clang version 11.0.0 (https://github.com/llvm/llvm-project.git 313d89724ce3ccf66c1c51849903e1e6d184dd85)"
+0x00000069: "fib2.c"
+0x00000070: "/usr/local/google/home/azakai/Dev/2-binaryen"
+0x0000009d: "fib"
+0x000000a1: "int"
+0x000000a5: "main"
+0x000000aa: "n"
+0x000000ac: "a"
+0x000000ae: "b"
+0x000000b0: "i"
+0x000000b2: "t"
+
+.debug_ranges contents:
+00000000 00000005 0000003d
+00000000 0000003e 00000044
+00000000 <End of list>
+(module
+ (type $none_=>_none (func))
+ (type $none_=>_i32 (func (result i32)))
+ (type $i32_=>_i32 (func (param i32) (result i32)))
+ (type $i32_i32_=>_i32 (func (param i32 i32) (result i32)))
+ (import "env" "memory" (memory $0 256 256))
+ (import "env" "__indirect_function_table" (table $timport$1 1 funcref))
+ (global $global$0 (mut i32) (i32.const 5243904))
+ (global $global$1 i32 (i32.const 1024))
+ (export "__wasm_call_ctors" (func $__wasm_call_ctors))
+ (export "main" (func $main))
+ (export "__data_end" (global $global$1))
+ (func $__wasm_call_ctors
+ )
+ (func $fib (param $0 i32) (result i32)
+  (local $1 i32)
+  (local $2 i32)
+  (local $3 i32)
+  (local $4 i32)
+  ;; code offset: 0xa
+  (local.set $1
+   ;; code offset: 0x8
+   (i32.const 1)
+  )
+  ;; code offset: 0xc
+  (block $label$1
+   ;; code offset: 0x13
+   (br_if $label$1
+    ;; code offset: 0x12
+    (i32.lt_s
+     ;; code offset: 0xe
+     (local.get $0)
+     ;; code offset: 0x10
+     (i32.const 1)
+    )
+   )
+   ;; code offset: 0x17
+   (local.set $2
+    ;; code offset: 0x15
+    (i32.const 0)
+   )
+   ;; code offset: 0x1b
+   (local.set $3
+    ;; code offset: 0x19
+    (i32.const 0)
+   )
+   ;; code offset: 0x1d
+   (loop $label$2
+    ;; code offset: 0x26
+    (local.set $1
+     ;; code offset: 0x25
+     (i32.add
+      ;; code offset: 0x21
+      (local.tee $4
+       ;; code offset: 0x1f
+       (local.get $1)
+      )
+      ;; code offset: 0x23
+      (local.get $2)
+     )
+    )
+    ;; code offset: 0x2a
+    (local.set $2
+     ;; code offset: 0x28
+     (local.get $4)
+    )
+    ;; code offset: 0x36
+    (br_if $label$2
+     ;; code offset: 0x35
+     (i32.ne
+      ;; code offset: 0x31
+      (local.tee $3
+       ;; code offset: 0x30
+       (i32.add
+        ;; code offset: 0x2c
+        (local.get $3)
+        ;; code offset: 0x2e
+        (i32.const 1)
+       )
+      )
+      ;; code offset: 0x33
+      (local.get $0)
+     )
+    )
+   )
+  )
+  ;; code offset: 0x3a
+  (local.get $1)
+ )
+ (func $__original_main (result i32)
+  ;; code offset: 0x41
+  (call $fib
+   ;; code offset: 0x3f
+   (i32.const 6)
+  )
+ )
+ (func $main (param $0 i32) (param $1 i32) (result i32)
+  ;; code offset: 0x46
+  (call $__original_main)
+ )
+ ;; custom section ".debug_info", size 168
+ ;; custom section ".debug_loc", size 143
+ ;; custom section ".debug_ranges", size 24
+ ;; custom section ".debug_abbrev", size 131
+ ;; custom section ".debug_line", size 183
+ ;; custom section ".debug_str", size 180
+ ;; custom section "producers", size 127
+)
diff --git a/test/passes/fib2_emptylocspan.passes b/test/passes/fib2_emptylocspan.passes
new file mode 100644
index 000000000..edbfb02ae
--- /dev/null
+++ b/test/passes/fib2_emptylocspan.passes
@@ -0,0 +1 @@
+dwarfdump_roundtrip_dwarfdump_g
diff --git a/test/passes/fib2_emptylocspan.wasm b/test/passes/fib2_emptylocspan.wasm
new file mode 100644
index 000000000..94e6cb5b9
--- /dev/null
+++ b/test/passes/fib2_emptylocspan.wasm