Source map fixes (#6550)

* Keep debug locations at function start

The `fn_prolog_epilog.debugInfo` test is failing otherwise, since there
was debug information associated to the nop instruction at the beginning
of the function.

* Do not clear the debug information when reaching the end of the source map

The last segment should extend to the end of the function.

* Propagate debug location from the function prolog to its first instruction

* Fix printing of epilogue location

The text parser no longer propagates locations to the epilogue, so we
should always print the location if there is one.

* Fix debug location smearing

The debug location of the last instruction should not smear into the
function epilogue, and a debug location from a previous function should
not smear into the prologue of the current function.

4 files changed, 30 insertions, 2 deletions

diff --git a/test/binaryen.js/sourcemap.js.txt b/test/binaryen.js/sourcemap.js.txt
index edb2d86a7..046ad029c 100644
--- a/test/binaryen.js/sourcemap.js.txt
+++ b/test/binaryen.js/sourcemap.js.txt
@@ -5,4 +5,4 @@ module.c
 020: u  r  c  e  M  a  p  p  i  n  g  U  R  L  0f m  
 030: o  d  u  l  e  .  w  a  s  m  .  m  a  p 
 
-{"version":3,"sources":["module.c"],"names":[],"mappings":"wBAAE"}
+{"version":3,"sources":["module.c"],"names":[],"mappings":"wBAAE,E"}
diff --git a/test/fib-dbg.wasm.fromBinary b/test/fib-dbg.wasm.fromBinary
index bc90702d3..f1b263234 100644
--- a/test/fib-dbg.wasm.fromBinary
+++ b/test/fib-dbg.wasm.fromBinary
@@ -209,11 +209,12 @@
      (br $label$4)
     )
    )
+   ;;@ fib.c:8:0
    (return
-    ;;@ fib.c:8:0
     (local.get $4)
    )
   )
+  ;;@ fib.c:8:0
  )
  (func $runPostSets
   (local $0 i32)
diff --git a/test/lit/debug/source-map-smearing.wast b/test/lit/debug/source-map-smearing.wast
new file mode 100644
index 000000000..875bec9d3
--- /dev/null
+++ b/test/lit/debug/source-map-smearing.wast
@@ -0,0 +1,22 @@
+;; RUN: wasm-opt %s -g -o %t.wasm -osm %t.wasm.map
+;; RUN: echo >> %t.wasm.map
+;; RUN: cat %t.wasm.map | filecheck %s
+
+;; Also test with StackIR, which should have identical results.
+;;
+;; RUN: wasm-opt %s --generate-stack-ir -o %t.wasm -osm %t.map -g -q
+;; RUN: echo >> %t.wasm.map
+;; RUN: cat %t.wasm.map | filecheck %s
+
+;; Check that the debug locations do not smear beyond a function
+;; epilogue to the next function. The encoded segment 'C' means that
+;; the previous segment is indeed one-byte long.
+;; CHECK: {"version":3,"sources":["foo"],"names":[],"mappings":"yBAAC,C,GACC"}
+(module
+  (func $0
+    ;;@ foo:1:1
+  )
+  (func $1
+    ;;@ foo:2:2
+  )
+)
diff --git a/test/lit/debug/source-map-stop.wast b/test/lit/debug/source-map-stop.wast
index d075d5686..cdc06505e 100644
--- a/test/lit/debug/source-map-stop.wast
+++ b/test/lit/debug/source-map-stop.wast
@@ -3,6 +3,11 @@
 ;; RUN: wasm-opt %s -g -o %t.wasm -osm %t.wasm.map
 ;; RUN: wasm-opt %t.wasm -ism %t.wasm.map -S -o - | filecheck %s
 
+;; Also test with StackIR, which should have identical results.
+;;
+;; RUN: wasm-opt %s --generate-stack-ir -o %t.wasm -osm %t.map -g -q
+;; RUN: wasm-opt %t.wasm -ism %t.map -q -o - -S | filecheck %s
+
 ;; Verify that writing to a source map and reading it back does not "smear"
 ;; debug info across adjacent instructions. The debug info in the output should
 ;; be identical to the input.