[Branch Hints] Fix if hint flip in Vacuum (#7713)

Author: kripken

src/passes/Vacuum.cpp

@@ -19,6 +19,7 @@
 //
 
 #include <ir/block-utils.h>
+#include <ir/branch-hints.h>
 #include <ir/drop.h>
 #include <ir/effects.h>
 #include <ir/iteration.h>
@@ -297,6 +298,7 @@ struct Vacuum : public WalkerPass<ExpressionStackWalker<Vacuum>> {
         curr->ifFalse = nullptr;
         curr->condition =
           Builder(*getModule()).makeUnary(EqZInt32, curr->condition);
+        BranchHints::flip(curr, getFunction());
       } else if (curr->ifTrue->is<Drop>() && curr->ifFalse->is<Drop>()) {
         // instead of dropping both sides, drop the if, if they are the same
         // type

test/lit/passes/vacuum-branch-hints.wast

@@ -0,0 +1,38 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+;; RUN: wasm-opt %s --vacuum -all -S -o - | filecheck %s
+
+(module
+ ;; CHECK:      (func $if (type $0) (param $x i32)
+ ;; CHECK-NEXT:  (@metadata.code.branch_hint "\01")
+ ;; CHECK-NEXT:  (if
+ ;; CHECK-NEXT:   (i32.eqz
+ ;; CHECK-NEXT:    (i32.eqz
+ ;; CHECK-NEXT:     (local.get $x)
+ ;; CHECK-NEXT:    )
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:   (then
+ ;; CHECK-NEXT:    (call $if
+ ;; CHECK-NEXT:     (local.get $x)
+ ;; CHECK-NEXT:    )
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $if (param $x i32)
+  ;; When we flip the if, the hint should flip too.
+  (@metadata.code.branch_hint "\00")
+  (if
+   (i32.eqz
+    (local.get $x)
+   )
+   (then
+    (nop)
+   )
+   (else
+    (call $if
+     (local.get $x)
+    )
+   )
+  )
+ )
+)
+