[turbofan] Elide fp32 convert for const compares

src/compiler/machine-operator-reducer.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/machine-operator-reducer.h"
 
 #include "src/base/bits.h"
 #include "src/base/division-by-constant.h"
 #include "src/codegen.h"
 #include "src/compiler/diamond.h"
@@ skipping 990 matching lines @@
   Uint32Matcher mrhs(node->InputAt(1));
   if (mlhs.HasValue() && mrhs.HasValue()) {
     return ReplaceFloat64(bit_cast<double>(
         (bit_cast<uint64_t>(mlhs.Value()) & V8_UINT64_C(0xFFFFFFFF)) |
         (static_cast<uint64_t>(mrhs.Value()) << 32)));
   }
   return NoChange();
 }
 
 
+namespace {
+
+bool IsFloat64RepresentableAsFloat32(const Float64Matcher& m) {
+  if (m.HasValue()) {
+    double v = m.Value();
+    float fv = static_cast<float>(v);
+    return static_cast<double>(fv) == v;
+  }
+  return false;
+}
+
+}  // namespace
+
+
 Reduction MachineOperatorReducer::ReduceFloat64Compare(Node* node) {
   DCHECK((IrOpcode::kFloat64Equal == node->opcode()) ||
          (IrOpcode::kFloat64LessThan == node->opcode()) ||
          (IrOpcode::kFloat64LessThanOrEqual == node->opcode()));
   // As all Float32 values have an exact representation in Float64, comparing
   // two Float64 values both converted from Float32 is equivalent to comparing
-  // the original Float32s, so we can ignore the conversions.
+  // the original Float32s, so we can ignore the conversions. We can also reduce
+  // comparisons of converted Float64 values against constants that can be
+  // represented exactly as Float32.
   Float64BinopMatcher m(node);
-  if (m.left().IsChangeFloat32ToFloat64() &&
-      m.right().IsChangeFloat32ToFloat64()) {
+  if ((m.left().IsChangeFloat32ToFloat64() &&
+       m.right().IsChangeFloat32ToFloat64()) ||
+      (m.left().IsChangeFloat32ToFloat64() &&
+       IsFloat64RepresentableAsFloat32(m.right())) ||
+      (IsFloat64RepresentableAsFloat32(m.left()) &&
+       m.right().IsChangeFloat32ToFloat64())) {
     switch (node->opcode()) {
       case IrOpcode::kFloat64Equal:
         node->set_op(machine()->Float32Equal());
         break;
       case IrOpcode::kFloat64LessThan:
         node->set_op(machine()->Float32LessThan());
         break;
       case IrOpcode::kFloat64LessThanOrEqual:
         node->set_op(machine()->Float32LessThanOrEqual());
         break;
       default:
         return NoChange();
     }
-    node->ReplaceInput(0, m.left().InputAt(0));
-    node->ReplaceInput(1, m.right().InputAt(0));
+    node->ReplaceInput(
+        0, m.left().HasValue()
+               ? Float32Constant(static_cast<float>(m.left().Value()))
+               : m.left().InputAt(0));
+    node->ReplaceInput(
+        1, m.right().HasValue()
+               ? Float32Constant(static_cast<float>(m.right().Value()))
+               : m.right().InputAt(0));
     return Changed(node);
   }
   return NoChange();
 }
 
 
 CommonOperatorBuilder* MachineOperatorReducer::common() const {
   return jsgraph()->common();
 }
 
 
 MachineOperatorBuilder* MachineOperatorReducer::machine() const {
   return jsgraph()->machine();
 }
 
 
 Graph* MachineOperatorReducer::graph() const { return jsgraph()->graph(); }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8