[turbofan] Fix invalid comparison operator narrowing.

src/compiler/x64/instruction-selector-x64.cc

Index: src/compiler/x64/instruction-selector-x64.cc
diff --git a/src/compiler/x64/instruction-selector-x64.cc b/src/compiler/x64/instruction-selector-x64.cc
index 8e54897d814281686c98a1869306f4de6c6f6918..7315b22beab771571284b2acd99454ec56eb32ca 100644
--- a/src/compiler/x64/instruction-selector-x64.cc
+++ b/src/compiler/x64/instruction-selector-x64.cc
@@ -1581,10 +1581,7 @@ void VisitCompare(InstructionSelector* selector, InstructionCode opcode,
 // Tries to match the size of the given opcode to that of the operands, if
 // possible.
 InstructionCode TryNarrowOpcodeSize(InstructionCode opcode, Node* left,
-                                    Node* right) {
-  if (opcode != kX64Cmp32 && opcode != kX64Test32) {
-    return opcode;
-  }
+                                    Node* right, FlagsContinuation* cont) {
   // Currently, if one of the two operands is not a Load, we don't know what its
   // machine representation is, so we bail out.
   // TODO(epertoso): we can probably get some size information out of immediates
@@ -1594,19 +1591,39 @@ InstructionCode TryNarrowOpcodeSize(InstructionCode opcode, Node* left,
   }
   // If the load representations don't match, both operands will be
   // zero/sign-extended to 32bit.
-  LoadRepresentation left_representation = LoadRepresentationOf(left->op());
-  if (left_representation != LoadRepresentationOf(right->op())) {
-    return opcode;
-  }
-  switch (left_representation.representation()) {
-    case MachineRepresentation::kBit:
-    case MachineRepresentation::kWord8:
-      return opcode == kX64Cmp32 ? kX64Cmp8 : kX64Test8;
-    case MachineRepresentation::kWord16:
-      return opcode == kX64Cmp32 ? kX64Cmp16 : kX64Test16;
-    default:
-      return opcode;
+  MachineType left_type = LoadRepresentationOf(left->op());
+  MachineType right_type = LoadRepresentationOf(right->op());
+  if (left_type == right_type) {
+    switch (left_type.representation()) {
+      case MachineRepresentation::kBit:
+      case MachineRepresentation::kWord8: {
+        if (opcode == kX64Test32) return kX64Test8;
+        if (opcode == kX64Cmp32) {
+          if (left_type.semantic() == MachineSemantic::kUint32) {
+            cont->OverwriteUnsignedIfSigned();
+          } else {
+            CHECK_EQ(MachineSemantic::kInt32, left_type.semantic());
+          }
+          return kX64Cmp8;
+        }
+        break;
+      }
+      case MachineRepresentation::kWord16:
+        if (opcode == kX64Test32) return kX64Test16;
+        if (opcode == kX64Cmp32) {
+          if (left_type.semantic() == MachineSemantic::kUint32) {
+            cont->OverwriteUnsignedIfSigned();
+          } else {
+            CHECK_EQ(MachineSemantic::kInt32, left_type.semantic());
+          }
+          return kX64Cmp16;
+        }
+        break;
+      default:
+        break;
+    }
   }
+  return opcode;
 }
 
 // Shared routine for multiple word compare operations.
@@ -1616,7 +1633,7 @@ void VisitWordCompare(InstructionSelector* selector, Node* node,
   Node* left = node->InputAt(0);
   Node* right = node->InputAt(1);
 
-  opcode = TryNarrowOpcodeSize(opcode, left, right);
+  opcode = TryNarrowOpcodeSize(opcode, left, right, cont);
 
   // If one of the two inputs is an immediate, make sure it's on the right, or
   // if one of the two inputs is a memory operand, make sure it's on the left.