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author | Dan Gohman <gohman@apple.com> | 2009-06-16 19:52:01 +0000 |
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committer | Dan Gohman <gohman@apple.com> | 2009-06-16 19:52:01 +0000 |
commit | a7726c31a78f30ca04ddd6c12dbe1c66dedebada (patch) | |
tree | 5a24d2c0527d2a08d4452a32893df0dc77412b2d /lib/Analysis | |
parent | fa4b3bd66505a2efd6be7b23cc9466e5b4a4b00f (diff) | |
download | external_llvm-a7726c31a78f30ca04ddd6c12dbe1c66dedebada.zip external_llvm-a7726c31a78f30ca04ddd6c12dbe1c66dedebada.tar.gz external_llvm-a7726c31a78f30ca04ddd6c12dbe1c66dedebada.tar.bz2 |
Instcombine's ShrinkDemandedConstant may strip bits out of constants,
obscuring what would otherwise be a low-bits mask. Use ComputeMaskedBits
to compute what ShrinkDemandedConstant knew about to reconstruct a
low-bits mask value.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73540 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Analysis')
-rw-r--r-- | lib/Analysis/ScalarEvolution.cpp | 21 |
1 files changed, 18 insertions, 3 deletions
diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp index ca805bd..3731fdf 100644 --- a/lib/Analysis/ScalarEvolution.cpp +++ b/lib/Analysis/ScalarEvolution.cpp @@ -68,6 +68,7 @@ #include "llvm/Analysis/ConstantFolding.h" #include "llvm/Analysis/Dominators.h" #include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/ValueTracking.h" #include "llvm/Assembly/Writer.h" #include "llvm/Target/TargetData.h" #include "llvm/Support/CommandLine.h" @@ -2394,14 +2395,28 @@ SCEVHandle ScalarEvolution::createSCEV(Value *V) { if (CI->isAllOnesValue()) return getSCEV(U->getOperand(0)); const APInt &A = CI->getValue(); - unsigned Ones = A.countTrailingOnes(); - if (APIntOps::isMask(Ones, A)) + + // Instcombine's ShrinkDemandedConstant may strip bits out of + // constants, obscuring what would otherwise be a low-bits mask. + // Use ComputeMaskedBits to compute what ShrinkDemandedConstant + // knew about to reconstruct a low-bits mask value. + unsigned LZ = A.countLeadingZeros(); + unsigned BitWidth = A.getBitWidth(); + APInt AllOnes = APInt::getAllOnesValue(BitWidth); + APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); + ComputeMaskedBits(U->getOperand(0), AllOnes, KnownZero, KnownOne, TD); + + APInt EffectiveMask = APInt::getLowBitsSet(BitWidth, BitWidth - LZ); + + if (LZ != 0 && !((~A & ~KnownZero) & EffectiveMask)) { return getZeroExtendExpr(getTruncateExpr(getSCEV(U->getOperand(0)), - IntegerType::get(Ones)), + IntegerType::get(BitWidth - LZ)), U->getType()); + } } break; + case Instruction::Or: // If the RHS of the Or is a constant, we may have something like: // X*4+1 which got turned into X*4|1. Handle this as an Add so loop |