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Use APInt's umul_ov instead of rolling our own overflow detection.

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llvm-svn: 128380
This commit is contained in:
Benjamin Kramer 2011-03-27 15:04:38 +00:00
parent c234349939
commit ea0ac8fafa
1 changed files with 6 additions and 5 deletions
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11
lib/Transforms/InstCombine/InstCombineCalls.cpp
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@ -487,14 +487,15 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
APInt RHSKnownOne(BitWidth, 0);
ComputeMaskedBits(RHS, Mask, RHSKnownZero, RHSKnownOne);
// Get the largest possible values for each operand, extended to be large
// enough so that every possible product of two BitWidth-sized ints fits.
APInt LHSMax = (~LHSKnownZero).zext(BitWidth*2);
APInt RHSMax = (~RHSKnownZero).zext(BitWidth*2);
// Get the largest possible values for each operand.
APInt LHSMax = ~LHSKnownZero;
APInt RHSMax = ~RHSKnownZero;
// If multiplying the maximum values does not overflow then we can turn
// this into a plain NUW mul.
if ((LHSMax * RHSMax).getActiveBits() <= BitWidth) {
bool Overflow;
LHSMax.umul_ov(RHSMax, Overflow);
if (!Overflow) {
Value *Mul = Builder->CreateNUWMul(LHS, RHS, "umul_with_overflow");
Constant *V[] = {
UndefValue::get(LHS->getType()),