[turbofan] Take the immediate size in account when narrowing ia32/x64 word comparison operators.

src/compiler/ia32/instruction-selector-ia32.cc

Index: src/compiler/ia32/instruction-selector-ia32.cc
diff --git a/src/compiler/ia32/instruction-selector-ia32.cc b/src/compiler/ia32/instruction-selector-ia32.cc
index 6228670c1b27880a3df6aae065f3d2925ee982e4..0489d551ddfb8296bb4dbd0c5c7ef620ef6d0972 100644
--- a/src/compiler/ia32/instruction-selector-ia32.cc
+++ b/src/compiler/ia32/instruction-selector-ia32.cc
@@ -1172,6 +1172,26 @@ void VisitCompare(InstructionSelector* selector, InstructionCode opcode,
   VisitCompare(selector, opcode, g.UseRegister(left), g.Use(right), cont);
 }
 
+bool GetMachineRepresentation(Node* node,

[Benedikt Meurer, 2016/05/04 04:05:47]

Maybe rename this to something like InferMachineRepresentation?

[epertoso, 2016/05/04 08:58:03]

Done.

+                              MachineRepresentation* representation) {
+  if (node->opcode() == IrOpcode::kLoad) {
+    *representation = LoadRepresentationOf(node->op()).representation();
+    return true;
+  }
+  if (node->opcode() != IrOpcode::kInt32Constant) {
+    return false;
+  }
+  uint32_t value = OpParameter<uint32_t>(node->op());

[Benedikt Meurer, 2016/05/04 04:05:47]

UBSAN will not be happy with this OpParameter. You need to use
OpParameter<int32_t>

[epertoso, 2016/05/04 08:58:02]

Done. Didn't see it was a reinterpret_cast.

+  if (is_uint8(value)) {
+    *representation = MachineRepresentation::kWord8;
+  } else if (is_uint16(value)) {
+    *representation = MachineRepresentation::kWord16;
+  } else {
+    *representation = MachineRepresentation::kWord32;
+  }
+  return true;
+}
+
 // Tries to match the size of the given opcode to that of the operands, if
 // possible.
 InstructionCode TryNarrowOpcodeSize(InstructionCode opcode, Node* left,
@@ -1179,20 +1199,22 @@ InstructionCode TryNarrowOpcodeSize(InstructionCode opcode, Node* left,
   if (opcode != kIA32Cmp && opcode != kIA32Test) {
     return opcode;
   }
-  // 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
-  // and phi nodes.
-  if (left->opcode() != IrOpcode::kLoad || right->opcode() != IrOpcode::kLoad) {
+  // We only do this if at least one of the two operands is a load.
+  // TODO(epertoso): we can probably get some size information out of phi nodes.
+  if (left->opcode() != IrOpcode::kLoad && right->opcode() != IrOpcode::kLoad) {
+    return opcode;
+  }
+  MachineRepresentation left_representation, right_representation;
+  if (!GetMachineRepresentation(left, &left_representation) ||
+      !GetMachineRepresentation(right, &right_representation)) {
     return opcode;
   }
-  // If the load representations don't match, both operands will be
+  // If the 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())) {
+  if (left_representation != right_representation) {
     return opcode;
   }
-  switch (left_representation.representation()) {
+  switch (left_representation) {
     case MachineRepresentation::kBit:
     case MachineRepresentation::kWord8:
       return opcode == kIA32Cmp ? kIA32Cmp8 : kIA32Test8;
@@ -1240,10 +1262,33 @@ void VisitWordCompare(InstructionSelector* selector, Node* node,
 
   // Match immediates on right side of comparison.
   if (g.CanBeImmediate(right)) {
-    if (g.CanBeMemoryOperand(opcode, node, left)) {
-      // TODO(epertoso): we should use `narrowed_opcode' here once we match
-      // immediates too.
-      return VisitCompareWithMemoryOperand(selector, opcode, left,
+    if (g.CanBeMemoryOperand(narrowed_opcode, node, left)) {
+      // If we're truncating the immediate (32 bits to 16 or 8), comparison
+      // semantics should take the signedness/unsignedness of the op into
+      // account.
+      if (narrowed_opcode != opcode &&
+          LoadRepresentationOf(left->op()).IsUnsigned()) {
+        switch (cont->condition()) {
+          case FlagsCondition::kSignedLessThan:
+            cont->OverwriteAndNegateIfEqual(FlagsCondition::kUnsignedLessThan);
+            break;
+          case FlagsCondition::kSignedGreaterThan:
+            cont->OverwriteAndNegateIfEqual(
+                FlagsCondition::kUnsignedGreaterThan);
+            break;
+          case FlagsCondition::kSignedLessThanOrEqual:
+            cont->OverwriteAndNegateIfEqual(
+                FlagsCondition::kUnsignedLessThanOrEqual);
+            break;
+          case FlagsCondition::kSignedGreaterThanOrEqual:
+            cont->OverwriteAndNegateIfEqual(
+                FlagsCondition::kUnsignedGreaterThanOrEqual);
+            break;
+          default:
+            break;
+        }
+      }
+      return VisitCompareWithMemoryOperand(selector, narrowed_opcode, left,
                                            g.UseImmediate(right), cont);
     }
     return VisitCompare(selector, opcode, g.Use(left), g.UseImmediate(right),