diff options
| -rw-r--r-- | lib/Analysis/ScalarEvolution.cpp | 13 | ||||
| -rw-r--r-- | test/Analysis/ScalarEvolution/and-xor.ll | 8 |
2 files changed, 21 insertions, 0 deletions
diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp index 3480a31..3ecb302 100644 --- a/lib/Analysis/ScalarEvolution.cpp +++ b/lib/Analysis/ScalarEvolution.cpp @@ -2203,6 +2203,19 @@ SCEVHandle ScalarEvolution::createSCEV(Value *V) { // If the RHS of xor is -1, then this is a not operation. if (CI->isAllOnesValue()) return getNotSCEV(getSCEV(U->getOperand(0))); + + // Model xor(and(x, C), C) as and(~x, C), if C is a low-bits mask. + // This is a variant of the check for xor with -1, and it handles + // the case where instcombine has trimmed non-demanded bits out + // of an xor with -1. + if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U->getOperand(0))) + if (ConstantInt *LCI = dyn_cast<ConstantInt>(BO->getOperand(1))) + if (BO->getOpcode() == Instruction::And && + LCI->getValue() == CI->getValue()) + if (const SCEVZeroExtendExpr *Z = + dyn_cast<SCEVZeroExtendExpr>(getSCEV(U->getOperand(0)))) + return getZeroExtendExpr(getNotSCEV(Z->getOperand()), + U->getType()); } break; diff --git a/test/Analysis/ScalarEvolution/and-xor.ll b/test/Analysis/ScalarEvolution/and-xor.ll new file mode 100644 index 0000000..94cca83 --- /dev/null +++ b/test/Analysis/ScalarEvolution/and-xor.ll @@ -0,0 +1,8 @@ +; RUN: llvm-as < %s | opt -scalar-evolution -analyze -disable-output \ +; RUN: | grep {\\--> (zext} | count 2 + +define i32 @foo(i32 %x) { + %n = and i32 %x, 255 + %y = xor i32 %n, 255 + ret i32 %y +} |