Bug 931489 - IonMonkey: Use range analysis to avoid testing for special cases in PowHalf. r=nbp

js/src/jit/MIR.h

@@ -3673,8 +3673,15 @@ class MPowHalf
   : public MUnaryInstruction,
     public DoublePolicy<0>
 {
+    bool operandIsNeverNegativeInfinity_;
+    bool operandIsNeverNegativeZero_;
+    bool operandIsNeverNaN_;
+
     MPowHalf(MDefinition *input)
-      : MUnaryInstruction(input)
+      : MUnaryInstruction(input),
+        operandIsNeverNegativeInfinity_(false),
+        operandIsNeverNegativeZero_(false),
+        operandIsNeverNaN_(false)
     {
         setResultType(MIRType_Double);
         setMovable();
@@ -3688,12 +3695,22 @@ class MPowHalf
     bool congruentTo(MDefinition *ins) const {
         return congruentIfOperandsEqual(ins);
     }
+    bool operandIsNeverNegativeInfinity() const {
+        return operandIsNeverNegativeInfinity_;
+    }
+    bool operandIsNeverNegativeZero() const {
+        return operandIsNeverNegativeZero_;
+    }
+    bool operandIsNeverNaN() const {
+        return operandIsNeverNaN_;
+    }
     TypePolicy *typePolicy() {
         return this;
     }
     AliasSet getAliasSet() const {
         return AliasSet::None();
     }
+    void collectRangeInfo();
 };
 
 // Inline implementation of Math.random().

js/src/jit/RangeAnalysis.cpp

@@ -2424,3 +2424,13 @@ MNot::collectRangeInfo()
 {
     operandIsNeverNaN_ = !Range(operand()).canBeNaN();
 }
+
+void
+MPowHalf::collectRangeInfo()
+{
+    Range inputRange(input());
+    operandIsNeverNegativeInfinity_ = !inputRange.canBeInfiniteOrNaN() ||
+                                      inputRange.hasInt32LowerBound();
+    operandIsNeverNegativeZero_ = !inputRange.canBeZero();
+    operandIsNeverNaN_ = !inputRange.canBeNaN();
+}

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

@@ -551,19 +551,29 @@ CodeGeneratorX86Shared::visitPowHalfD(LPowHalfD *ins)
 
     Label done, sqrt;
 
+    if (!ins->mir()->operandIsNeverNegativeInfinity()) {
         // Branch if not -Infinity.
         masm.loadConstantDouble(NegativeInfinity(), ScratchFloatReg);
-    masm.branchDouble(Assembler::DoubleNotEqualOrUnordered, input, ScratchFloatReg, &sqrt);
+
+        Assembler::DoubleCondition cond = Assembler::DoubleNotEqualOrUnordered;
+        if (ins->mir()->operandIsNeverNaN())
+            cond = Assembler::DoubleNotEqual;
+        masm.branchDouble(cond, input, ScratchFloatReg, &sqrt);
 
         // Math.pow(-Infinity, 0.5) == Infinity.
         masm.xorpd(input, input);
         masm.subsd(ScratchFloatReg, input);
         masm.jump(&done);
 
-    // Math.pow(-0, 0.5) == 0 == Math.pow(0, 0.5). Adding 0 converts any -0 to 0.
         masm.bind(&sqrt);
+    }
+
+    if (!ins->mir()->operandIsNeverNegativeZero()) {
+        // Math.pow(-0, 0.5) == 0 == Math.pow(0, 0.5). Adding 0 converts any -0 to 0.
         masm.xorpd(ScratchFloatReg, ScratchFloatReg);
         masm.addsd(ScratchFloatReg, input);
+    }
+
     masm.sqrtsd(input, input);
 
     masm.bind(&done);

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

@@ -171,6 +171,9 @@ class LPowHalfD : public LInstructionHelper<1, 1, 0>
     const LDefinition *output() {
         return getDef(0);
     }
+    MPowHalf *mir() const {
+        return mir_->toPowHalf();
+    }
 };
 
 // Takes a tableswitch with an integer to decide