Bug 1073016 - Optimize LRound and LRoundF on x86/x64. r=nbp

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

@@ -1903,18 +1903,13 @@ CodeGeneratorX86Shared::visitRound(LRound *lir)
     FloatRegister scratch = ScratchDoubleReg;
     Register output = ToRegister(lir->output());
 
-    Label negative, end, bailout;
+    Label negativeOrZero, negative, end, bailout;
 
-    // Branch to a slow path for negative inputs. Doesn't catch NaN or -0.
+    // Branch to a slow path for non-positive inputs. Doesn't catch NaN.
     masm.xorpd(scratch, scratch);
-    masm.branchDouble(Assembler::DoubleLessThan, input, scratch, &negative);
+    masm.branchDouble(Assembler::DoubleLessThanOrEqual, input, scratch, &negativeOrZero);
 
-    // Bail on negative-zero.
-    masm.branchNegativeZero(input, output, &bailout);
-    if (!bailoutFrom(&bailout, lir->snapshot()))
-        return false;
-
-    // Input is non-negative. Add the biggest double less than 0.5 and
+    // Input is positive. Add the biggest double less than 0.5 and
     // truncate, rounding down (because if the input is the biggest double less
     // than 0.5, adding 0.5 would undesirably round up to 1). Note that we have
     // to add the input to the temp register because we're not allowed to
@@ -1926,7 +1921,21 @@ CodeGeneratorX86Shared::visitRound(LRound *lir)
 
     masm.jump(&end);
 
-    // Input is negative, but isn't -0.
+    // Input is negative, +0 or -0.
+    masm.bind(&negativeOrZero);
+    // Branch on negative input.
+    masm.j(Assembler::NotEqual, &negative);
+
+    // Bail on negative-zero.
+    masm.branchNegativeZero(input, output, &bailout, /* maybeNonZero = */ false);
+    if (!bailoutFrom(&bailout, lir->snapshot()))
+        return false;
+
+    // Input is +0
+    masm.xor32(output, output);
+    masm.jump(&end);
+
+    // Input is negative.
     masm.bind(&negative);
     masm.loadConstantDouble(0.5, temp);
 
@@ -1984,16 +1993,11 @@ CodeGeneratorX86Shared::visitRoundF(LRoundF *lir)
     FloatRegister scratch = ScratchFloat32Reg;
     Register output = ToRegister(lir->output());
 
-    Label negative, end, bailout;
+    Label negativeOrZero, negative, end, bailout;
 
-    // Branch to a slow path for negative inputs. Doesn't catch NaN or -0.
+    // Branch to a slow path for non-positive inputs. Doesn't catch NaN.
     masm.xorps(scratch, scratch);
-    masm.branchFloat(Assembler::DoubleLessThan, input, scratch, &negative);
-
-    // Bail on negative-zero.
-    masm.branchNegativeZeroFloat32(input, output, &bailout);
-    if (!bailoutFrom(&bailout, lir->snapshot()))
-        return false;
+    masm.branchFloat(Assembler::DoubleLessThanOrEqual, input, scratch, &negativeOrZero);
 
     // Input is non-negative. Add the biggest float less than 0.5 and truncate,
     // rounding down (because if the input is the biggest float less than 0.5,
@@ -2008,7 +2012,21 @@ CodeGeneratorX86Shared::visitRoundF(LRoundF *lir)
 
     masm.jump(&end);
 
-    // Input is negative, but isn't -0.
+    // Input is negative, +0 or -0.
+    masm.bind(&negativeOrZero);
+    // Branch on negative input.
+    masm.j(Assembler::NotEqual, &negative);
+
+    // Bail on negative-zero.
+    masm.branchNegativeZeroFloat32(input, output, &bailout);
+    if (!bailoutFrom(&bailout, lir->snapshot()))
+        return false;
+
+    // Input is +0.
+    masm.xor32(output, output);
+    masm.jump(&end);
+
+    // Input is negative.
     masm.bind(&negative);
     masm.loadConstantFloat32(0.5f, temp);
 

js/src/jit/shared/MacroAssembler-x86-shared.cpp

@@ -197,7 +197,8 @@ MacroAssemblerX86Shared::buildOOLFakeExitFrame(void *fakeReturnAddr)
 void
 MacroAssemblerX86Shared::branchNegativeZero(FloatRegister reg,
                                             Register scratch,
-                                            Label *label)
+                                            Label *label,
+                                            bool maybeNonZero)
 {
     // Determines whether the low double contained in the XMM register reg
     // is equal to -0.0.
@@ -205,12 +206,14 @@ MacroAssemblerX86Shared::branchNegativeZero(FloatRegister reg,
 #if defined(JS_CODEGEN_X86)
     Label nonZero;
 
-    // Compare to zero. Lets through {0, -0}.
-    xorpd(ScratchDoubleReg, ScratchDoubleReg);
-
-    // If reg is non-zero, jump to nonZero.
-    branchDouble(DoubleNotEqual, reg, ScratchDoubleReg, &nonZero);
+    // if not already compared to zero
+    if (maybeNonZero) {
+        // Compare to zero. Lets through {0, -0}.
+        xorpd(ScratchDoubleReg, ScratchDoubleReg);
 
+        // If reg is non-zero, jump to nonZero.
+        branchDouble(DoubleNotEqual, reg, ScratchDoubleReg, &nonZero);
+    }
     // Input register is either zero or negative zero. Retrieve sign of input.
     movmskpd(reg, scratch);
 

js/src/jit/shared/MacroAssembler-x86-shared.h

@@ -90,7 +90,7 @@ class MacroAssemblerX86Shared : public Assembler
         j(ConditionFromDoubleCondition(cond), label);
     }
 
-    void branchNegativeZero(FloatRegister reg, Register scratch, Label *label);
+    void branchNegativeZero(FloatRegister reg, Register scratch, Label *label, bool  maybeNonZero = true);
     void branchNegativeZeroFloat32(FloatRegister reg, Register scratch, Label *label);
 
     void move32(Imm32 imm, Register dest) {