diff options
Diffstat (limited to 'llvm/lib/Transforms')
| -rw-r--r-- | llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp b/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp index abd6a81da1e..8b016eceff0 100644 --- a/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp +++ b/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp @@ -1316,6 +1316,7 @@ static bool detectCTLZIdiom(Loop *CurLoop, PHINode *&PhiX, return false; // step 2: detect instructions corresponding to "x.next = x >> 1" + // TODO: Support loops that use LShr. if (!DefX || DefX->getOpcode() != Instruction::AShr) return false; ConstantInt *Shft = dyn_cast<ConstantInt>(DefX->getOperand(1)); @@ -1397,6 +1398,13 @@ bool LoopIdiomRecognize::recognizeAndInsertCTLZ() { // parent function RunOnLoop. BasicBlock *PH = CurLoop->getLoopPreheader(); Value *InitX = PhiX->getIncomingValueForBlock(PH); + + // Make sure the initial value can't be negative otherwise the ashr in the + // loop might never reach zero which would make the loop infinite. + // TODO: Support loops that use lshr and wouldn't need this check. + if (!isKnownNonNegative(InitX, *DL)) + return false; + // If we check X != 0 before entering the loop we don't need a zero // check in CTLZ intrinsic, but only if Cnt Phi is not used outside of the // loop (if it is used we count CTLZ(X >> 1)). |
