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Add a new target hook "predictableSelectIsExpensive".
This will be used to determine whether it's profitable to turn a select into a branch when the branch is likely to be predicted. Currently enabled for everything but Atom on X86 and Cortex-A9 devices on ARM. I'm not entirely happy with the name of this flag, suggestions welcome ;) git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@156233 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -150,6 +150,12 @@ public:
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/// that should be avoided.
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bool isJumpExpensive() const { return JumpIsExpensive; }
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/// isPredictableSelectExpensive - Return true if selects are only cheaper
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/// than branches if the branch is unlikely to be predicted right.
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bool isPredictableSelectExpensive() const {
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return predictableSelectIsExpensive;
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}
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/// getSetCCResultType - Return the ValueType of the result of SETCC
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/// operations. Also used to obtain the target's preferred type for
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/// the condition operand of SELECT and BRCOND nodes. In the case of
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@ -2028,6 +2034,10 @@ protected:
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/// optimization.
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bool benefitFromCodePlacementOpt;
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/// predictableSelectIsExpensive - Tells the code generator that select is
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/// more expensive than a branch if the branch is usually predicted right.
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bool predictableSelectIsExpensive;
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private:
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/// isLegalRC - Return true if the value types that can be represented by the
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/// specified register class are all legal.
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@ -605,6 +605,7 @@ TargetLowering::TargetLowering(const TargetMachine &tm,
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IntDivIsCheap = false;
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Pow2DivIsCheap = false;
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JumpIsExpensive = false;
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predictableSelectIsExpensive = false;
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StackPointerRegisterToSaveRestore = 0;
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ExceptionPointerRegister = 0;
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ExceptionSelectorRegister = 0;
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@ -824,6 +824,9 @@ ARMTargetLowering::ARMTargetLowering(TargetMachine &TM)
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benefitFromCodePlacementOpt = true;
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// Prefer likely predicted branches to selects on out-of-order cores.
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predictableSelectIsExpensive = Subtarget->isCortexA9();
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setMinFunctionAlignment(Subtarget->isThumb() ? 1 : 2);
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}
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@ -1243,6 +1243,9 @@ X86TargetLowering::X86TargetLowering(X86TargetMachine &TM)
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setPrefLoopAlignment(4); // 2^4 bytes.
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benefitFromCodePlacementOpt = true;
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// Predictable cmov don't hurt on atom because it's in-order.
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predictableSelectIsExpensive = !Subtarget->isAtom();
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setPrefFunctionAlignment(4); // 2^4 bytes.
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}
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