Handle negative input in inlined Math.round on Intel CPUs.

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index 8892142cb1b7411ffbe085ea7ba1a43b2703084d..3f7b85d5521310b482dabb7cbbdb729eb9261406 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -3734,47 +3734,75 @@ void LCodeGen::DoMathFloor(LUnaryMathOperation* instr) {
 
 void LCodeGen::DoMathRound(LUnaryMathOperation* instr) {
   CpuFeatures::Scope scope(SSE2);
-  XMMRegister xmm_scratch = xmm0;
   Register output_reg = ToRegister(instr->result());
   XMMRegister input_reg = ToDoubleRegister(instr->value());
-
-  Label below_half, done;
-  // xmm_scratch = 0.5
+  XMMRegister xmm_scratch = xmm0;
   ExternalReference one_half = ExternalReference::address_of_one_half();
+  ExternalReference minus_one_half =
+      ExternalReference::address_of_minus_one_half();
+  bool minus_zero_check =
+      instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero);
+
   __ movdbl(xmm_scratch, Operand::StaticVariable(one_half));
-  __ ucomisd(xmm_scratch, input_reg);
-  __ j(above, &below_half);
-  // xmm_scratch = input + 0.5
-  __ addsd(xmm_scratch, input_reg);
 
-  // Compute Math.floor(value + 0.5).
-  // Use truncating instruction (OK because input is positive).
-  __ cvttsd2si(output_reg, Operand(xmm_scratch));
+  if (CpuFeatures::IsSupported(SSE4_1) && !minus_zero_check) {
+    CpuFeatures::Scope scope(SSE4_1);
 
-  // Overflow is signalled with minint.
-  __ cmp(output_reg, 0x80000000u);
-  DeoptimizeIf(equal, instr->environment());
-  __ jmp(&done);
+    __ addsd(xmm_scratch, input_reg);
+    __ roundsd(xmm_scratch, input_reg, Assembler::kRoundDown);
+    __ cvttsd2si(output_reg, Operand(xmm_scratch));
+    // Overflow is signalled with minint.
+    __ cmp(output_reg, 0x80000000u);
+    __ RecordComment("D2I conversion overflow");
+    DeoptimizeIf(equal, instr->environment());
+  } else {
+    Label done, round_to_zero, below_one_half, do_not_compensate;
+    __ ucomisd(xmm_scratch, input_reg);
+    __ j(above, &below_one_half);
 
-  __ bind(&below_half);
+    // CVTTSD2SI rounds towards zero, since 0.5 <= x, we use floor(0.5 + x).
+    __ addsd(xmm_scratch, input_reg);
+    __ cvttsd2si(output_reg, Operand(xmm_scratch));
+    // Overflow is signalled with minint.
+    __ cmp(output_reg, 0x80000000u);
+    __ RecordComment("D2I conversion overflow");
+    DeoptimizeIf(equal, instr->environment());
+    __ jmp(&done);
 
-  // We return 0 for the input range [+0, 0.5[, or [-0.5, 0.5[ if
-  // we can ignore the difference between a result of -0 and +0.
-  if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
-    // If the sign is positive, we return +0.
-    __ movmskpd(output_reg, input_reg);
-    __ test(output_reg, Immediate(1));
-    DeoptimizeIf(not_zero, instr->environment());
-  } else {
-    // If the input is >= -0.5, we return +0.
-    __ mov(output_reg, Immediate(0xBF000000));
-    __ movd(xmm_scratch, Operand(output_reg));
-    __ cvtss2sd(xmm_scratch, xmm_scratch);
-    __ ucomisd(input_reg, xmm_scratch);
-    DeoptimizeIf(below, instr->environment());
+    __ bind(&below_one_half);
+    __ movdbl(xmm_scratch, Operand::StaticVariable(minus_one_half));
+    __ ucomisd(xmm_scratch, input_reg);
+    __ j(below_equal, &round_to_zero);
+
+    // CVTTSD2SI rounds towards zero, we use ceil(x - (-0.5)) and then
+    // compare and compensate.
+    __ subsd(input_reg, xmm_scratch);
+    __ cvttsd2si(output_reg, Operand(input_reg));
+    // Catch minint due to overflow, and to prevent overflow when compensating.
+    __ cmp(output_reg, 0x80000000u);
+    __ RecordComment("D2I conversion overflow");
+    DeoptimizeIf(equal, instr->environment());
+
+    __ cvtsi2sd(xmm_scratch, output_reg);
+    __ ucomisd(xmm_scratch, input_reg);
+    __ j(equal, &done);
+    __ sub(output_reg, Immediate(1));
+    // No overflow because we already ruled out minint.
+    __ jmp(&done);
+
+    __ bind(&round_to_zero);
+    // We return 0 for the input range [+0, 0.5[, or [-0.5, 0.5[ if
+    // we can ignore the difference between a result of -0 and +0.
+    if (minus_zero_check) {
+      // If the sign is positive, we return +0.
+      __ movmskpd(output_reg, input_reg);
+      __ test(output_reg, Immediate(1));
+      __ RecordComment("Minus zero");
+      DeoptimizeIf(not_zero, instr->environment());
+    }
+    __ Set(output_reg, Immediate(0));
+    __ bind(&done);
   }
-  __ Set(output_reg, Immediate(0));
-  __ bind(&done);
 }