Fix a bug with unreachable control flow in IRBuilder (#6558)

When branches target control flow structures other than blocks or loops,
the IRBuilder wraps those control flow structures with an extra block
for the branches to target in Binaryen IR. When the control flow
structure is unreachable because all its bodies are unreachable, the
wrapper block may still need to have a non-unreachable type if it is
targeted by branches. This is achieved by tracking whether the wrapper
block will be targeted by any branches and use the control flow
structure's original, non-unreachable type if so. However, this was not
properly tracked when moving into the `else` branch of an `if` or the
`catch`/`cath_all` handlers of a `try` block.

3 files changed, 148 insertions, 56 deletions

diff --git a/src/wasm-ir-builder.h b/src/wasm-ir-builder.h
index addbd1a30..3c4a52bea 100644
--- a/src/wasm-ir-builder.h
+++ b/src/wasm-ir-builder.h
@@ -311,9 +311,11 @@ private:
 
     ScopeCtx() : scope(NoScope{}) {}
     ScopeCtx(Scope scope) : scope(scope) {}
-    ScopeCtx(Scope scope, Name label) : scope(scope), label(label) {}
-    ScopeCtx(Scope scope, Name label, Name branchLabel)
-      : scope(scope), label(label), branchLabel(branchLabel) {}
+    ScopeCtx(Scope scope, Name label, bool labelUsed)
+      : scope(scope), label(label), labelUsed(labelUsed) {}
+    ScopeCtx(Scope scope, Name label, bool labelUsed, Name branchLabel)
+      : scope(scope), label(label), branchLabel(branchLabel),
+        labelUsed(labelUsed) {}
 
     static ScopeCtx makeFunc(Function* func) {
       return ScopeCtx(FuncScope{func});
@@ -324,20 +326,29 @@ private:
     static ScopeCtx makeIf(If* iff, Name originalLabel = {}) {
       return ScopeCtx(IfScope{iff, originalLabel});
     }
-    static ScopeCtx makeElse(If* iff, Name originalLabel, Name label) {
-      return ScopeCtx(ElseScope{iff, originalLabel}, label);
+    static ScopeCtx
+    makeElse(If* iff, Name originalLabel, Name label, bool labelUsed) {
+      return ScopeCtx(ElseScope{iff, originalLabel}, label, labelUsed);
     }
     static ScopeCtx makeLoop(Loop* loop) { return ScopeCtx(LoopScope{loop}); }
     static ScopeCtx makeTry(Try* tryy, Name originalLabel = {}) {
       return ScopeCtx(TryScope{tryy, originalLabel});
     }
-    static ScopeCtx
-    makeCatch(Try* tryy, Name originalLabel, Name label, Name branchLabel) {
-      return ScopeCtx(CatchScope{tryy, originalLabel}, label, branchLabel);
+    static ScopeCtx makeCatch(Try* tryy,
+                              Name originalLabel,
+                              Name label,
+                              bool labelUsed,
+                              Name branchLabel) {
+      return ScopeCtx(
+        CatchScope{tryy, originalLabel}, label, labelUsed, branchLabel);
     }
-    static ScopeCtx
-    makeCatchAll(Try* tryy, Name originalLabel, Name label, Name branchLabel) {
-      return ScopeCtx(CatchAllScope{tryy, originalLabel}, label, branchLabel);
+    static ScopeCtx makeCatchAll(Try* tryy,
+                                 Name originalLabel,
+                                 Name label,
+                                 bool labelUsed,
+                                 Name branchLabel) {
+      return ScopeCtx(
+        CatchAllScope{tryy, originalLabel}, label, labelUsed, branchLabel);
     }
     static ScopeCtx makeTryTable(TryTable* trytable, Name originalLabel = {}) {
       return ScopeCtx(TryTableScope{trytable, originalLabel});
diff --git a/src/wasm/wasm-ir-builder.cpp b/src/wasm/wasm-ir-builder.cpp
index ccd2ee77a..6322a5786 100644
--- a/src/wasm/wasm-ir-builder.cpp
+++ b/src/wasm/wasm-ir-builder.cpp
@@ -810,10 +810,11 @@ Result<> IRBuilder::visitElse() {
   }
   auto originalLabel = scope.getOriginalLabel();
   auto label = scope.label;
+  auto labelUsed = scope.labelUsed;
   auto expr = finishScope();
   CHECK_ERR(expr);
   iff->ifTrue = *expr;
-  pushScope(ScopeCtx::makeElse(iff, originalLabel, label));
+  pushScope(ScopeCtx::makeElse(iff, originalLabel, label, labelUsed));
   return Ok{};
 }
 
@@ -830,6 +831,7 @@ Result<> IRBuilder::visitCatch(Name tag) {
   }
   auto originalLabel = scope.getOriginalLabel();
   auto label = scope.label;
+  auto labelUsed = scope.labelUsed;
   auto branchLabel = scope.branchLabel;
   auto expr = finishScope();
   CHECK_ERR(expr);
@@ -839,7 +841,8 @@ Result<> IRBuilder::visitCatch(Name tag) {
     tryy->catchBodies.push_back(*expr);
   }
   tryy->catchTags.push_back(tag);
-  pushScope(ScopeCtx::makeCatch(tryy, originalLabel, label, branchLabel));
+  pushScope(
+    ScopeCtx::makeCatch(tryy, originalLabel, label, labelUsed, branchLabel));
   // Push a pop for the exception payload.
   auto params = wasm.getTag(tag)->sig.params;
   if (params != Type::none) {
@@ -861,6 +864,7 @@ Result<> IRBuilder::visitCatchAll() {
   }
   auto originalLabel = scope.getOriginalLabel();
   auto label = scope.label;
+  auto labelUsed = scope.labelUsed;
   auto branchLabel = scope.branchLabel;
   auto expr = finishScope();
   CHECK_ERR(expr);
@@ -869,7 +873,8 @@ Result<> IRBuilder::visitCatchAll() {
   } else {
     tryy->catchBodies.push_back(*expr);
   }
-  pushScope(ScopeCtx::makeCatchAll(tryy, originalLabel, label, branchLabel));
+  pushScope(
+    ScopeCtx::makeCatchAll(tryy, originalLabel, label, labelUsed, branchLabel));
   return Ok{};
 }
 
diff --git a/test/lit/wat-kitchen-sink.wast b/test/lit/wat-kitchen-sink.wast
index 772d3f5df..8e4d26d4f 100644
--- a/test/lit/wat-kitchen-sink.wast
+++ b/test/lit/wat-kitchen-sink.wast
@@ -62,49 +62,49 @@
 
  ;; CHECK:      (type $24 (func (param v128 i32) (result v128)))
 
- ;; CHECK:      (type $25 (func (param i32) (result i32 i64)))
+ ;; CHECK:      (type $25 (func (param i32) (result i32)))
+
+ ;; CHECK:      (type $26 (func (param i32) (result i32 i64)))
 
  ;; CHECK:      (type $packed-i16 (array (mut i16)))
 
  ;; CHECK:      (type $any-array (array (mut anyref)))
 
- ;; CHECK:      (type $28 (func (param stringref)))
+ ;; CHECK:      (type $29 (func (param stringref)))
 
- ;; CHECK:      (type $29 (func (param stringref stringref) (result i32)))
+ ;; CHECK:      (type $30 (func (param stringref stringref) (result i32)))
 
- ;; CHECK:      (type $30 (func (param i64 v128) (result v128)))
+ ;; CHECK:      (type $31 (func (param i64 v128) (result v128)))
 
- ;; CHECK:      (type $31 (func (param i64 v128)))
+ ;; CHECK:      (type $32 (func (param i64 v128)))
 
  ;; CHECK:      (type $cont-bind-before-func (func (param i32 i64 i32 i64) (result f32)))
 
  ;; CHECK:      (type $cont-bind-before (cont $cont-bind-before-func))
 
- ;; CHECK:      (type $34 (func (result structref arrayref)))
-
- ;; CHECK:      (type $35 (func (result arrayref structref)))
+ ;; CHECK:      (type $35 (func (result structref arrayref)))
 
- ;; CHECK:      (type $36 (func (result i32 i64 (ref null $simple-cont))))
+ ;; CHECK:      (type $36 (func (result arrayref structref)))
 
- ;; CHECK:      (type $37 (func (param i32 i32)))
+ ;; CHECK:      (type $37 (func (result i32 i64 (ref null $simple-cont))))
 
- ;; CHECK:      (type $38 (func (param exnref)))
+ ;; CHECK:      (type $38 (func (param i32 i32)))
 
- ;; CHECK:      (type $39 (func (result anyref anyref)))
+ ;; CHECK:      (type $39 (func (param exnref)))
 
- ;; CHECK:      (type $40 (func (param i32 i32 f64 f64)))
+ ;; CHECK:      (type $40 (func (result anyref anyref)))
 
- ;; CHECK:      (type $41 (func (param i64)))
+ ;; CHECK:      (type $41 (func (param i32 i32 f64 f64)))
 
- ;; CHECK:      (type $42 (func (param v128) (result i32)))
+ ;; CHECK:      (type $42 (func (param i64)))
 
- ;; CHECK:      (type $43 (func (param v128 v128) (result v128)))
+ ;; CHECK:      (type $43 (func (param v128) (result i32)))
 
- ;; CHECK:      (type $44 (func (param v128 v128 v128) (result v128)))
+ ;; CHECK:      (type $44 (func (param v128 v128) (result v128)))
 
- ;; CHECK:      (type $45 (func (param i32 i32 i64 i64)))
+ ;; CHECK:      (type $45 (func (param v128 v128 v128) (result v128)))
 
- ;; CHECK:      (type $46 (func (param i32) (result i32)))
+ ;; CHECK:      (type $46 (func (param i32 i32 i64 i64)))
 
  ;; CHECK:      (type $47 (func (param i64) (result i32 i64)))
 
@@ -950,7 +950,7 @@
   drop
  )
 
- ;; CHECK:      (func $locals (type $37) (param $0 i32) (param $x i32)
+ ;; CHECK:      (func $locals (type $38) (param $0 i32) (param $x i32)
  ;; CHECK-NEXT:  (local $2 i32)
  ;; CHECK-NEXT:  (local $y i32)
  ;; CHECK-NEXT:  (drop
@@ -2567,7 +2567,7 @@
   )
  )
 
- ;; CHECK:      (func $try-table-throw-ref (type $38) (param $0 exnref)
+ ;; CHECK:      (func $try-table-throw-ref (type $39) (param $0 exnref)
  ;; CHECK-NEXT:  (throw_ref
  ;; CHECK-NEXT:   (local.get $0)
  ;; CHECK-NEXT:  )
@@ -2963,10 +2963,10 @@
   end
  )
 
- ;; CHECK:      (func $br-table-multivalue-glb (type $39) (result anyref anyref)
- ;; CHECK-NEXT:  (block $a (type $35) (result arrayref structref)
+ ;; CHECK:      (func $br-table-multivalue-glb (type $40) (result anyref anyref)
+ ;; CHECK-NEXT:  (block $a (type $36) (result arrayref structref)
  ;; CHECK-NEXT:   (return
- ;; CHECK-NEXT:    (block $b (type $34) (result structref arrayref)
+ ;; CHECK-NEXT:    (block $b (type $35) (result structref arrayref)
  ;; CHECK-NEXT:     (br_table $a $b
  ;; CHECK-NEXT:      (tuple.make 2
  ;; CHECK-NEXT:       (ref.null none)
@@ -3013,7 +3013,7 @@
   end
  )
 
- ;; CHECK:      (func $binary (type $40) (param $0 i32) (param $1 i32) (param $2 f64) (param $3 f64)
+ ;; CHECK:      (func $binary (type $41) (param $0 i32) (param $1 i32) (param $2 f64) (param $3 f64)
  ;; CHECK-NEXT:  (drop
  ;; CHECK-NEXT:   (i32.add
  ;; CHECK-NEXT:    (local.get $0)
@@ -3038,7 +3038,7 @@
   drop
  )
 
- ;; CHECK:      (func $unary (type $41) (param $0 i64)
+ ;; CHECK:      (func $unary (type $42) (param $0 i64)
  ;; CHECK-NEXT:  (drop
  ;; CHECK-NEXT:   (i64.eqz
  ;; CHECK-NEXT:    (local.get $0)
@@ -3387,7 +3387,7 @@
   drop
  )
 
- ;; CHECK:      (func $simd-extract (type $42) (param $0 v128) (result i32)
+ ;; CHECK:      (func $simd-extract (type $43) (param $0 v128) (result i32)
  ;; CHECK-NEXT:  (i32x4.extract_lane 3
  ;; CHECK-NEXT:   (local.get $0)
  ;; CHECK-NEXT:  )
@@ -3409,7 +3409,7 @@
   i32x4.replace_lane 2
  )
 
- ;; CHECK:      (func $simd-shuffle (type $43) (param $0 v128) (param $1 v128) (result v128)
+ ;; CHECK:      (func $simd-shuffle (type $44) (param $0 v128) (param $1 v128) (result v128)
  ;; CHECK-NEXT:  (i8x16.shuffle 0 1 2 3 4 5 6 7 16 17 18 19 20 21 22 23
  ;; CHECK-NEXT:   (local.get $0)
  ;; CHECK-NEXT:   (local.get $1)
@@ -3421,7 +3421,7 @@
   i8x16.shuffle 0 1 2 3 4 5 6 7 16 17 18 19 20 21 22 23
  )
 
- ;; CHECK:      (func $simd-ternary (type $44) (param $0 v128) (param $1 v128) (param $2 v128) (result v128)
+ ;; CHECK:      (func $simd-ternary (type $45) (param $0 v128) (param $1 v128) (param $2 v128) (result v128)
  ;; CHECK-NEXT:  (v128.bitselect
  ;; CHECK-NEXT:   (local.get $0)
  ;; CHECK-NEXT:   (local.get $1)
@@ -3531,7 +3531,7 @@
   data.drop $passive
  )
 
- ;; CHECK:      (func $memory-copy (type $45) (param $0 i32) (param $1 i32) (param $2 i64) (param $3 i64)
+ ;; CHECK:      (func $memory-copy (type $46) (param $0 i32) (param $1 i32) (param $2 i64) (param $3 i64)
  ;; CHECK-NEXT:  (memory.copy $mimport$0 $mimport$0
  ;; CHECK-NEXT:   (local.get $0)
  ;; CHECK-NEXT:   (local.get $1)
@@ -3602,7 +3602,7 @@
   return
  )
 
- ;; CHECK:      (func $return-one (type $46) (param $0 i32) (result i32)
+ ;; CHECK:      (func $return-one (type $25) (param $0 i32) (result i32)
  ;; CHECK-NEXT:  (return
  ;; CHECK-NEXT:   (local.get $0)
  ;; CHECK-NEXT:  )
@@ -3640,7 +3640,7 @@
   return
  )
 
- ;; CHECK:      (func $return-two-second-unreachable (type $25) (param $0 i32) (result i32 i64)
+ ;; CHECK:      (func $return-two-second-unreachable (type $26) (param $0 i32) (result i32 i64)
  ;; CHECK-NEXT:  (drop
  ;; CHECK-NEXT:   (local.get $0)
  ;; CHECK-NEXT:  )
@@ -3654,7 +3654,7 @@
   return
  )
 
- ;; CHECK:      (func $return-two-second-unreachable-tuple (type $25) (param $0 i32) (result i32 i64)
+ ;; CHECK:      (func $return-two-second-unreachable-tuple (type $26) (param $0 i32) (result i32 i64)
  ;; CHECK-NEXT:  (return
  ;; CHECK-NEXT:   (tuple.make 2
  ;; CHECK-NEXT:    (local.get $0)
@@ -4513,7 +4513,7 @@
   string.const "\00\00\00"
  )
 
- ;; CHECK:      (func $string-measure (type $28) (param $0 stringref)
+ ;; CHECK:      (func $string-measure (type $29) (param $0 stringref)
  ;; CHECK-NEXT:  (drop
  ;; CHECK-NEXT:   (string.measure_wtf8
  ;; CHECK-NEXT:    (local.get $0)
@@ -4570,7 +4570,7 @@
   stringview_wtf16.length
  )
 
- ;; CHECK:      (func $string-encode (type $28) (param $0 stringref)
+ ;; CHECK:      (func $string-encode (type $29) (param $0 stringref)
  ;; CHECK-NEXT:  (drop
  ;; CHECK-NEXT:   (string.encode_wtf8
  ;; CHECK-NEXT:    (local.get $0)
@@ -4641,7 +4641,7 @@
   string.concat
  )
 
- ;; CHECK:      (func $string-eq (type $29) (param $0 stringref) (param $1 stringref) (result i32)
+ ;; CHECK:      (func $string-eq (type $30) (param $0 stringref) (param $1 stringref) (result i32)
  ;; CHECK-NEXT:  (string.eq
  ;; CHECK-NEXT:   (local.get $0)
  ;; CHECK-NEXT:   (local.get $1)
@@ -4653,7 +4653,7 @@
   string.eq
  )
 
- ;; CHECK:      (func $string-compare (type $29) (param $0 stringref) (param $1 stringref) (result i32)
+ ;; CHECK:      (func $string-compare (type $30) (param $0 stringref) (param $1 stringref) (result i32)
  ;; CHECK-NEXT:  (string.compare
  ;; CHECK-NEXT:   (local.get $0)
  ;; CHECK-NEXT:   (local.get $1)
@@ -4849,7 +4849,7 @@
  ;; CHECK-NEXT:   (local.get $0)
  ;; CHECK-NEXT:  )
  ;; CHECK-NEXT:  (drop
- ;; CHECK-NEXT:   (call_indirect $timport$0 (type $30)
+ ;; CHECK-NEXT:   (call_indirect $timport$0 (type $31)
  ;; CHECK-NEXT:    (local.get $1)
  ;; CHECK-NEXT:    (local.get $2)
  ;; CHECK-NEXT:    (local.get $0)
@@ -4911,7 +4911,7 @@
  ;; CHECK-NEXT:   (local.get $0)
  ;; CHECK-NEXT:  )
  ;; CHECK-NEXT:  (drop
- ;; CHECK-NEXT:   (call_indirect $timport$0 (type $30)
+ ;; CHECK-NEXT:   (call_indirect $timport$0 (type $31)
  ;; CHECK-NEXT:    (local.get $1)
  ;; CHECK-NEXT:    (local.get $2)
  ;; CHECK-NEXT:    (local.get $0)
@@ -4983,7 +4983,7 @@
  ;; CHECK-NEXT:  (return_call_indirect $funcs (type $void)
  ;; CHECK-NEXT:   (local.get $0)
  ;; CHECK-NEXT:  )
- ;; CHECK-NEXT:  (return_call_indirect $timport$0 (type $31)
+ ;; CHECK-NEXT:  (return_call_indirect $timport$0 (type $32)
  ;; CHECK-NEXT:   (local.get $1)
  ;; CHECK-NEXT:   (local.get $2)
  ;; CHECK-NEXT:   (local.get $0)
@@ -5042,7 +5042,7 @@
  ;; CHECK-NEXT:  (return_call_indirect $funcs (type $void)
  ;; CHECK-NEXT:   (local.get $0)
  ;; CHECK-NEXT:  )
- ;; CHECK-NEXT:  (return_call_indirect $timport$0 (type $31)
+ ;; CHECK-NEXT:  (return_call_indirect $timport$0 (type $32)
  ;; CHECK-NEXT:   (local.get $1)
  ;; CHECK-NEXT:   (local.get $2)
  ;; CHECK-NEXT:   (local.get $0)
@@ -5090,7 +5090,7 @@
  ;; CHECK-NEXT:    (drop
  ;; CHECK-NEXT:     (block $block (result (ref $to-f32-cont))
  ;; CHECK-NEXT:      (tuple.drop 3
- ;; CHECK-NEXT:       (block $block0 (type $36) (result i32 i64 (ref null $simple-cont))
+ ;; CHECK-NEXT:       (block $block0 (type $37) (result i32 i64 (ref null $simple-cont))
  ;; CHECK-NEXT:        (local.set $f
  ;; CHECK-NEXT:         (resume $simple-cont (tag $empty $block) (tag $tag-pair-to-pair $block0)
  ;; CHECK-NEXT:          (i32.const 0)
@@ -5280,4 +5280,80 @@
   (param (ref $submany))
   (param (ref $all-types))
  )
+
+ ;; The if is unreachable except through the break; make sure this is
+ ;; parse correctly
+ ;; CHECK:      (func $if-else-br-return (type $25) (param $a i32) (result i32)
+ ;; CHECK-NEXT:  (block $label
+ ;; CHECK-NEXT:   (if
+ ;; CHECK-NEXT:    (local.get $a)
+ ;; CHECK-NEXT:    (then
+ ;; CHECK-NEXT:     (br $label)
+ ;; CHECK-NEXT:    )
+ ;; CHECK-NEXT:    (else
+ ;; CHECK-NEXT:     (return
+ ;; CHECK-NEXT:      (i32.const 0)
+ ;; CHECK-NEXT:     )
+ ;; CHECK-NEXT:    )
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (i32.const 1)
+ ;; CHECK-NEXT: )
+ (func $if-else-br-return (param $a i32) (result i32)
+  (if (local.get $a)
+   (then
+    (br 0)
+   )
+   (else
+    (return (i32.const 0))
+   )
+  )
+  (i32.const 1)
+ )
+
+ ;; CHECK:      (func $try-br-catch-all-return (type $void)
+ ;; CHECK-NEXT:  (block $label
+ ;; CHECK-NEXT:   (try
+ ;; CHECK-NEXT:    (do
+ ;; CHECK-NEXT:     (br $label)
+ ;; CHECK-NEXT:    )
+ ;; CHECK-NEXT:    (catch_all
+ ;; CHECK-NEXT:     (return)
+ ;; CHECK-NEXT:    )
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $try-br-catch-all-return
+  (try
+   (do
+    (br 0)
+   )
+   (catch_all
+     (return)
+   )
+  )
+ )
+
+ ;; CHECK:      (func $try-br-catch-return (type $void)
+ ;; CHECK-NEXT:  (block $label
+ ;; CHECK-NEXT:   (try
+ ;; CHECK-NEXT:    (do
+ ;; CHECK-NEXT:     (br $label)
+ ;; CHECK-NEXT:    )
+ ;; CHECK-NEXT:    (catch $empty
+ ;; CHECK-NEXT:     (return)
+ ;; CHECK-NEXT:    )
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $try-br-catch-return
+  (try
+   (do
+    (br 0)
+   )
+   (catch $empty
+     (return)
+   )
+  )
+ )
 )