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Teach ScalarEvolution how to recognize another xor(and(x, C), C) case.

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If C is a single bit and the and gets analyzed as a truncate and
zero-extend, the xor can be represnted as an add.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73664 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-06-18 00:00:20 +00:00
parent fc3641b07a
commit 820528331f
2 changed files with 22 additions and 6 deletions
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23
lib/Analysis/ScalarEvolution.cpp
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@ -2453,10 +2453,25 @@ SCEVHandle ScalarEvolution::createSCEV(Value *V) {
LCI->getValue() == CI->getValue())
if (const SCEVZeroExtendExpr *Z =
dyn_cast<SCEVZeroExtendExpr>(getSCEV(U->getOperand(0)))) {
SCEVHandle ZO = Z->getOperand();
if (APIntOps::isMask(getTypeSizeInBits(ZO->getType()),
CI->getValue()))
return getZeroExtendExpr(getNotSCEV(ZO), U->getType());
const Type *UTy = U->getType();
SCEVHandle Z0 = Z->getOperand();
const Type *Z0Ty = Z0->getType();
unsigned Z0TySize = getTypeSizeInBits(Z0Ty);
// If C is a low-bits mask, the zero extend is zerving to
// mask off the high bits. Complement the operand and
// re-apply the zext.
if (APIntOps::isMask(Z0TySize, CI->getValue()))
return getZeroExtendExpr(getNotSCEV(Z0), UTy);
// If C is a single bit, it may be in the sign-bit position
// before the zero-extend. In this case, represent the xor
// using an add, which is equivalent, and re-apply the zext.
APInt Trunc = APInt(CI->getValue()).trunc(Z0TySize);
if (APInt(Trunc).zext(getTypeSizeInBits(UTy)) == CI->getValue() &&
Trunc.isSignBit())
return getZeroExtendExpr(getAddExpr(Z0, getConstant(Trunc)),
UTy);
}
}
break;

5
test/Analysis/ScalarEvolution/xor-and.ll
View File

@ -1,6 +1,7 @@
; RUN: llvm-as < %s | opt -scalar-evolution -disable-output -analyze | grep {\\--> %z}
; RUN: llvm-as < %s | opt -scalar-evolution -disable-output -analyze \
; RUN: | grep {\\--> (zext i4 (-8 + (trunc i64 (8 \\* %x) to i4)) to i64)}
; ScalarEvolution shouldn't try to analyze %s into something like
; ScalarEvolution shouldn't try to analyze %z into something like
; --> (zext i4 (-1 + (-1 * (trunc i64 (8 * %x) to i4))) to i64)
define i64 @foo(i64 %x) {