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Fold fcmp in cases where value is provably non-negative. By Arch Robison.

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This patch folds fcmp in some cases of interest in Julia. The patch adds a function CannotBeOrderedLessThanZero that returns true if a value is provably not less than zero. I.e. the function returns true if the value is provably -0, +0, positive, or a NaN. The patch extends InstructionSimplify.cpp to fold instances of fcmp where:
 - the predicate is olt or uge
 - the first operand is provably not less than zero
 - the second operand is zero
The motivation for handling these cases optimizing away domain checks for sqrt in Julia for common idioms such as sqrt(x*x+y*y)..

http://reviews.llvm.org/D6972



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227298 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Elena Demikhovsky
2015-01-28 08:03:58 +00:00
parent e02ee8cf05
commit b5c82c079a
4 changed files with 132 additions and 0 deletions
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lib/Analysis/ValueTracking.cpp
+53
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@@ -2044,6 +2044,59 @@ bool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) {
return false;
}
bool llvm::CannotBeOrderedLessThanZero(const Value *V, unsigned Depth) {
if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
return !CFP->getValueAPF().isNegative() || CFP->getValueAPF().isZero();
if (Depth == 6)
return false; // Limit search depth.
const Operator *I = dyn_cast<Operator>(V);
if (!I) return false;
switch (I->getOpcode()) {
default: break;
case Instruction::FMul:
// x*x is always non-negative or a NaN.
if (I->getOperand(0) == I->getOperand(1))
return true;
// Fall through
case Instruction::FAdd:
case Instruction::FDiv:
case Instruction::FRem:
return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1) &&
CannotBeOrderedLessThanZero(I->getOperand(1), Depth+1);
case Instruction::FPExt:
case Instruction::FPTrunc:
// Widening/narrowing never change sign.
return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1);
case Instruction::Call:
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::exp:
case Intrinsic::exp2:
case Intrinsic::fabs:
case Intrinsic::sqrt:
return true;
case Intrinsic::powi:
if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
// powi(x,n) is non-negative if n is even.
if (CI->getBitWidth() <= 64 && CI->getSExtValue() % 2u == 0)
return true;
}
return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1);
case Intrinsic::fma:
case Intrinsic::fmuladd:
// x*x+y is non-negative if y is non-negative.
return I->getOperand(0) == I->getOperand(1) &&
CannotBeOrderedLessThanZero(I->getOperand(2), Depth+1);
}
break;
}
return false;
}
/// If the specified value can be set by repeating the same byte in memory,
/// return the i8 value that it is represented with. This is
/// true for all i8 values obviously, but is also true for i32 0, i32 -1,