[Branch Hints] Fix if hint flip in OptimizeInstructions (#7711)

Author: kripken

src/ir/branch-hints.h

@@ -103,7 +103,7 @@ inline void applyOrTo(Expression* from1,
                       Expression* from2,
                       Expression* to,
                       Function* func) {
-  // If one is likely then so is the from1 || from2. If both are unlikely then
+  // If one is likely then so is from1 || from2. If both are unlikely then
   // from1 || from2 is slightly more likely, but we assume our hints are nearly
   // certain, so we apply it.
   auto from1Hint = BranchHints::get(from1, func);

src/passes/OptimizeInstructions.cpp

@@ -25,6 +25,7 @@
 #include <ir/abstract.h>
 #include <ir/bits.h>
 #include <ir/boolean.h>
+#include <ir/branch-hints.h>
 #include <ir/cost.h>
 #include <ir/drop.h>
 #include <ir/effects.h>
@@ -1171,6 +1172,7 @@ struct OptimizeInstructions
           // flip if-else arms to get rid of an eqz
           curr->condition = unary->value;
           std::swap(curr->ifTrue, curr->ifFalse);
+          BranchHints::flip(curr, getFunction());
         }
       }
       if (curr->condition->type != Type::unreachable &&

test/lit/passes/optimize-instructions-branch-hints.wast

@@ -0,0 +1,32 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+;; RUN: wasm-opt %s --optimize-instructions -all -S -o - | filecheck %s
+
+(module
+ ;; CHECK:      (func $conditionals (type $0) (param $x i32) (result i32)
+ ;; CHECK-NEXT:  (@metadata.code.branch_hint "\01")
+ ;; CHECK-NEXT:  (if (result i32)
+ ;; CHECK-NEXT:   (local.get $x)
+ ;; CHECK-NEXT:   (then
+ ;; CHECK-NEXT:    (i32.const 1337)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:   (else
+ ;; CHECK-NEXT:    (i32.const 42)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $conditionals (param $x i32) (result i32)
+  ;; When we flip the if, the hint should flip too.
+  (@metadata.code.branch_hint "\00")
+  (if (result i32)
+   (i32.eqz
+    (local.get $x)
+   )
+   (then
+    (i32.const 42)
+   )
+   (else
+    (i32.const 1337)
+   )
+  )
+ )
+)