Bug 870356 - Fix IonMonkey Math.round bug on x86/x64 hardware without SSE 4.1. r=sstangl

js/src/ion/shared/CodeGenerator-x86-shared.cpp

@@ -326,6 +326,13 @@ CodeGeneratorX86Shared::bailoutIf(Assembler::Condition condition, LSnapshot *sna
     return bailout(BailoutJump(condition), snapshot);
 }
 
+bool
+CodeGeneratorX86Shared::bailoutIf(Assembler::DoubleCondition condition, LSnapshot *snapshot)
+{
+    JS_ASSERT(Assembler::NaNCondFromDoubleCondition(condition) == Assembler::NaN_HandledByCond);
+    return bailoutIf(Assembler::ConditionFromDoubleCondition(condition), snapshot);
+}
+
 bool
 CodeGeneratorX86Shared::bailoutFrom(Label *label, LSnapshot *snapshot)
 {
@@ -1289,8 +1296,12 @@ CodeGeneratorX86Shared::visitRound(LRound *lir)
         masm.addsd(input, temp);
 
         // Round toward -Infinity without the benefit of ROUNDSD.
-        Label testZero;
         {
+            // If input + 0.5 >= 0, input is a negative number >= -0.5 and the result is -0.
+            masm.compareDouble(Assembler::DoubleGreaterThanOrEqual, temp, scratch);
+            if (!bailoutIf(Assembler::DoubleGreaterThanOrEqual, lir->snapshot()))
+                return false;
+
             // Truncate and round toward zero.
             // This is off-by-one for everything but integer-valued inputs.
             masm.cvttsd2si(temp, output);
@@ -1300,19 +1311,13 @@ CodeGeneratorX86Shared::visitRound(LRound *lir)
 
             // Test whether the truncated double was integer-valued.
             masm.cvtsi2sd(output, scratch);
-            masm.branchDouble(Assembler::DoubleEqualOrUnordered, temp, scratch, &testZero);
+            masm.branchDouble(Assembler::DoubleEqualOrUnordered, temp, scratch, &end);
 
             // Input is not integer-valued, so we rounded off-by-one in the
             // wrong direction. Correct by subtraction.
             masm.subl(Imm32(1), output);
             // Cannot overflow: output was already checked against INT_MIN.
-
-            // Fall through to testZero.
         }
-
-        masm.bind(&testZero);
-        if (!bailoutIf(Assembler::Zero, lir->snapshot()))
-            return false;
     }
 
     masm.bind(&end);

js/src/ion/shared/CodeGenerator-x86-shared.h

@@ -50,6 +50,7 @@ class CodeGeneratorX86Shared : public CodeGeneratorShared
     MoveResolver::MoveOperand toMoveOperand(const LAllocation *a) const;
 
     bool bailoutIf(Assembler::Condition condition, LSnapshot *snapshot);
+    bool bailoutIf(Assembler::DoubleCondition condition, LSnapshot *snapshot);
     bool bailoutFrom(Label *label, LSnapshot *snapshot);
     bool bailout(LSnapshot *snapshot);
 

js/src/jit-test/tests/ion/bug870356.js

@@ -0,0 +1,33 @@
+function f1(x) {
+    return Math.round(x);
+}
+assertEq(f1(3.3), 3);
+assertEq(f1(-2.842170943040401e-14), -0);
+
+function f2(x) {
+    return Math.round(x);
+}
+assertEq(f2(3.3), 3);
+assertEq(f2(-1.3), -1);
+assertEq(f2(-1.8), -2);
+assertEq(f2(-0.9), -1);
+assertEq(f2(-0.6), -1);
+assertEq(f2(-0.4), -0);
+
+function f3(x) {
+    return Math.round(x);
+}
+assertEq(f3(0.1), 0);
+assertEq(f3(-0.5), -0);
+
+function f4(x) {
+    return Math.round(x);
+}
+assertEq(f4(0.1), 0);
+assertEq(f4(-0), -0);
+
+function f5(x) {
+    return Math.round(x);
+}
+assertEq(f5(2.9), 3);
+assertEq(f5(NaN), NaN);