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Teach ScalarEvolution to recognize x^-1 in the case where non-demanded
bits have been stripped out by instcombine. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72010 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -2203,6 +2203,19 @@ SCEVHandle ScalarEvolution::createSCEV(Value *V) {
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// If the RHS of xor is -1, then this is a not operation.
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if (CI->isAllOnesValue())
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return getNotSCEV(getSCEV(U->getOperand(0)));
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// Model xor(and(x, C), C) as and(~x, C), if C is a low-bits mask.
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// This is a variant of the check for xor with -1, and it handles
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// the case where instcombine has trimmed non-demanded bits out
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// of an xor with -1.
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if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U->getOperand(0)))
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if (ConstantInt *LCI = dyn_cast<ConstantInt>(BO->getOperand(1)))
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if (BO->getOpcode() == Instruction::And &&
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LCI->getValue() == CI->getValue())
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if (const SCEVZeroExtendExpr *Z =
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dyn_cast<SCEVZeroExtendExpr>(getSCEV(U->getOperand(0))))
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return getZeroExtendExpr(getNotSCEV(Z->getOperand()),
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U->getType());
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}
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break;
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8
test/Analysis/ScalarEvolution/and-xor.ll
Normal file
8
test/Analysis/ScalarEvolution/and-xor.ll
Normal file
@ -0,0 +1,8 @@
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; RUN: llvm-as < %s | opt -scalar-evolution -analyze -disable-output \
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; RUN: | grep {\\--> (zext} | count 2
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define i32 @foo(i32 %x) {
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%n = and i32 %x, 255
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%y = xor i32 %n, 255
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ret i32 %y
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}
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