fix block removal in remove-unused-brs, even if not taken, if named, we must preserve it

Author: kripken

src/passes/RemoveUnusedBrs.cpp

@@ -259,7 +259,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
             // so only do it if it looks useful, which it definitely is if
             //  (a) $somewhere is straight out (so the br out vanishes), and
             //  (b) this br_if is the only branch to that block (so the block will vanish)
-            if (brIf->name == block->name && BranchUtils::BranchSeeker::count(block, block->name) == 1) {
+            if (brIf->name == block->name && BranchUtils::BranchSeeker::countNamed(block, block->name) == 1) {
               // note that we could drop the last element here, it is a br we know for sure is removable,
               // but telling stealSlice to steal all to the end is more efficient, it can just truncate.
               list[i] = builder.makeIf(brIf->condition, builder.makeBreak(brIf->name), builder.stealSlice(block, i + 1, list.size()));
@@ -449,7 +449,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
             auto* br = list[0]->dynCast<Break>();
             if (br && br->condition && br->name == curr->name) {
               assert(!br->value); // can't, it would be dropped or last in the block
-              if (BranchUtils::BranchSeeker::count(curr, curr->name) == 1) {
+              if (BranchUtils::BranchSeeker::countNamed(curr, curr->name) == 1) {
                 // no other breaks to that name, so we can do this
                 Builder builder(*getModule());
                 replaceCurrent(builder.makeIf(

test/passes/remove-unused-brs.txt

@@ -4,6 +4,7 @@
  (type $2 (func (result i32)))
  (type $3 (func (param i32 i32) (result i32)))
  (type $4 (func (param i32 i32)))
+ (type $5 (func (param f32 i32 f32 i32 i32 f64 f32) (result i32)))
  (memory $0 256 256)
  (func $b0-yes (type $0) (param $i1 i32)
   (block $topmost
@@ -975,4 +976,39 @@
    )
   )
  )
+ (func $untaken-brs-might-prevent-block-removal (type $5) (param $0 f32) (param $1 i32) (param $2 f32) (param $3 i32) (param $4 i32) (param $5 f64) (param $6 f32) (result i32)
+  (block $label$0 (result i32)
+   (block $label$1
+    (br_if $label$1
+     (i32.const 607395945)
+    )
+    (br_if $label$1
+     (unreachable.load16_s offset=3 align=1
+      (select
+       (call $untaken-brs-might-prevent-block-removal
+        (f32.const 1.4904844647389837e-07)
+        (br_if $label$0
+         (i32.store16 offset=4 align=1
+          (i32.const 1900641)
+          (br $label$0
+           (i32.const 1628075109)
+          )
+         )
+         (i32.const 1764950569)
+        )
+        (f32.const 1.1910939690100655e-32)
+        (i32.const 1628057906)
+        (i32.const 859068982)
+        (f64.const 2.524518840347722e-258)
+        (f32.const -nan:0x40a63)
+       )
+       (i32.const 688529440)
+       (i32.const 1751478890)
+      )
+     )
+    )
+   )
+   (i32.const 1935947830)
+  )
+ )
 )

test/passes/remove-unused-brs.wast

@@ -866,5 +866,40 @@
       )
     )
   )
+  (func $untaken-brs-might-prevent-block-removal (param $0 f32) (param $1 i32) (param $2 f32) (param $3 i32) (param $4 i32) (param $5 f64) (param $6 f32) (result i32)
+   (block $label$0 (result i32)
+    (block $label$1 ;; this block has no taken brs, but we can't remove it without removing them first
+     (br_if $label$1
+      (i32.const 607395945)
+     )
+     (br_if $label$1
+      (i32.load16_s offset=3 align=1
+       (select
+        (call $untaken-brs-might-prevent-block-removal
+         (f32.const 1.4904844647389837e-07)
+         (br_if $label$0
+          (i32.store16 offset=4 align=1
+           (i32.const 1900641)
+           (br $label$0
+            (i32.const 1628075109)
+           )
+          )
+          (i32.const 1764950569)
+         )
+         (f32.const 1.1910939690100655e-32)
+         (i32.const 1628057906)
+         (i32.const 859068982)
+         (f64.const 2.524518840347722e-258)
+         (f32.const -nan:0x40a63)
+        )
+        (i32.const 688529440)
+        (i32.const 1751478890)
+       )
+      )
+     )
+    )
+    (i32.const 1935947830)
+   )
+  )
 )