Optimize double min/max by reducing the code size (reusing left register as result removes the need…

runtime/vm/intermediate_language_ia32.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_IA32.
 #if defined(TARGET_ARCH_IA32)
 
 #include "vm/intermediate_language.h"
 
 #include "lib/error.h"
@@ skipping 3624 matching lines @@
 
 
 LocationSummary* MathMinMaxInstr::MakeLocationSummary() const {
   if (result_cid() == kDoubleCid) {
     const intptr_t kNumInputs = 2;
     const intptr_t kNumTemps = 1;
     LocationSummary* summary =
         new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
     summary->set_in(0, Location::RequiresFpuRegister());
     summary->set_in(1, Location::RequiresFpuRegister());
-    summary->set_out(Location::RequiresFpuRegister());
+    // Reuse the left register so that code can be made shorter.
+    summary->set_out(Location::SameAsFirstInput());
     summary->set_temp(0, Location::RequiresRegister());
     return summary;
   }
   ASSERT(result_cid() == kSmiCid);
-  UNIMPLEMENTED();
-  return NULL;
+  const intptr_t kNumInputs = 2;
+  const intptr_t kNumTemps = 0;
+  LocationSummary* summary =
+      new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
+  summary->set_in(0, Location::RequiresRegister());
+  summary->set_in(1, Location::RequiresRegister());
+  // Reuse the left register so that code can be made shorter.
+  summary->set_out(Location::SameAsFirstInput());
+  return summary;
 }
 
 
 void MathMinMaxInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   ASSERT((op_kind() == MethodRecognizer::kMathMin) ||
          (op_kind() == MethodRecognizer::kMathMax));
+  const intptr_t is_min = (op_kind() == MethodRecognizer::kMathMin);
   if (result_cid() == kDoubleCid) {
-    Label done, returns_left, returns_nan, are_equal;
+    Label done, returns_nan, are_equal;
     XmmRegister left = locs()->in(0).fpu_reg();
     XmmRegister right = locs()->in(1).fpu_reg();
     XmmRegister result = locs()->out().fpu_reg();
     Register temp = locs()->temp(0).reg();
     __ comisd(left, right);
     __ j(PARITY_EVEN, &returns_nan, Assembler::kNearJump);
     __ j(EQUAL, &are_equal, Assembler::kNearJump);
-    const intptr_t is_min = (op_kind() == MethodRecognizer::kMathMin);
     const Condition double_condition =
         is_min ? TokenKindToDoubleCondition(Token::kLT)
                : TokenKindToDoubleCondition(Token::kGT);
-    __ j(double_condition, &returns_left, Assembler::kNearJump);
+    ASSERT(left == result);
+    __ j(double_condition, &done, Assembler::kNearJump);
     __ movsd(result, right);
     __ jmp(&done, Assembler::kNearJump);
 
-    __ Bind(&returns_left);
-    __ movsd(result, left);
-    __ jmp(&done, Assembler::kNearJump);
-
     __ Bind(&returns_nan);
     static double kNaN = NAN;
     __ movsd(result, Address::Absolute(reinterpret_cast<uword>(&kNaN)));
     __ jmp(&done, Assembler::kNearJump);
 
     __ Bind(&are_equal);
     Label left_is_negative;
     // Check for negative zero: -0.0 is equal 0.0 but min or max must return
     // -0.0 or 0.0 respectively.
     // Check for negative left value (get the sign bit):
     // - min -> left is negative ? left : right.
     // - max -> left is negative ? right : left
     // Check the sign bit.
     __ movmskpd(temp, left);
     __ testl(temp, Immediate(1));
-    __ j(NOT_ZERO, &left_is_negative, Assembler::kNearJump);
-    // Left is positive.
-    __ movsd(result, (is_min ? right : left));
-    __ jmp(&done, Assembler::kNearJump);
-
-    __ Bind(&left_is_negative);
-    __ movsd(result, (is_min ? left : right));
+    ASSERT(left == result);
+    if (is_min) {
+      __ j(NOT_ZERO, &done, Assembler::kNearJump);  // Negative -> return left.
+    } else {
+      __ j(ZERO, &done, Assembler::kNearJump);  // Positive -> return left.
+    }
+    __ movsd(result, right);
     __ Bind(&done);
     return;
   }
+
+  Label done;
   ASSERT(result_cid() == kSmiCid);
-  UNIMPLEMENTED();
+  Register left = locs()->in(0).reg();
+  Register right = locs()->in(1).reg();
+  Register result = locs()->out().reg();
+  __ cmpl(left, right);
+  if (is_min) {
+    ASSERT(result == left);
+    __ j(LESS_EQUAL, &done, Assembler::kNearJump);

[sra1, 2013/07/23 20:53:27]

CMOVLE result, right

Or is there some problem with CMOVcc?  I know CMOVcc r,[mem] does a load
regardless but this is not that case.

[srdjan, 2013/07/23 21:22:21]

Good suggestion. Currently we do not have cmovcc implemented in the assembler
(except signed test), but I will do that in a next CL. 

+  } else {
+    __ j(GREATER_EQUAL, &done, Assembler::kNearJump);
+  }
+  __ movl(result, right);
+  __ Bind(&done);
 }
 
 
 LocationSummary* UnarySmiOpInstr::MakeLocationSummary() const {
   const intptr_t kNumInputs = 1;
   return LocationSummary::Make(kNumInputs,
                                Location::SameAsFirstInput(),
                                LocationSummary::kNoCall);
 }
 
@@ skipping 1105 matching lines @@
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_IA32