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| author | Dan Gohman <gohman@apple.com> | 2009-05-21 02:28:33 +0000 |
|---|---|---|
| committer | Dan Gohman <gohman@apple.com> | 2009-05-21 02:28:33 +0000 |
| commit | 2bc21561cfce6fe595822c74fd56e99786c1b263 (patch) | |
| tree | 537c7db81d2ade0b3a765258ac8f71fd2900371b /lib/Analysis/ValueTracking.cpp | |
| parent | c308c5087f9aa950cb9a17144a3364e3b7bb8544 (diff) | |
| download | external_llvm-2bc21561cfce6fe595822c74fd56e99786c1b263.zip external_llvm-2bc21561cfce6fe595822c74fd56e99786c1b263.tar.gz external_llvm-2bc21561cfce6fe595822c74fd56e99786c1b263.tar.bz2 | |
Teach ValueTracking a new way to analyze PHI nodes, and and teach
Instcombine to be more aggressive about using SimplifyDemandedBits
on shift nodes. This allows a shift to be simplified to zero in the
included test case.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72204 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Analysis/ValueTracking.cpp')
| -rw-r--r-- | lib/Analysis/ValueTracking.cpp | 29 |
1 files changed, 27 insertions, 2 deletions
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp index c4f6faf..3c21e20 100644 --- a/lib/Analysis/ValueTracking.cpp +++ b/lib/Analysis/ValueTracking.cpp @@ -48,8 +48,9 @@ static unsigned getOpcode(const Value *V) { void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero, APInt &KnownOne, TargetData *TD, unsigned Depth) { + const unsigned MaxDepth = 6; assert(V && "No Value?"); - assert(Depth <= 6 && "Limit Search Depth"); + assert(Depth <= MaxDepth && "Limit Search Depth"); unsigned BitWidth = Mask.getBitWidth(); assert((V->getType()->isInteger() || isa<PointerType>(V->getType())) && "Not integer or pointer type!"); @@ -88,7 +89,7 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, KnownZero.clear(); KnownOne.clear(); // Start out not knowing anything. - if (Depth == 6 || Mask == 0) + if (Depth == MaxDepth || Mask == 0) return; // Limit search depth. User *I = dyn_cast<User>(V); @@ -522,6 +523,30 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, } } } + + // Otherwise take the unions of the known bit sets of the operands, + // taking conservative care to avoid excessive recursion. + if (Depth < MaxDepth - 1 && !KnownZero && !KnownOne) { + KnownZero = APInt::getAllOnesValue(BitWidth); + KnownOne = APInt::getAllOnesValue(BitWidth); + for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) { + // Skip direct self references. + if (P->getIncomingValue(i) == P) continue; + + KnownZero2 = APInt(BitWidth, 0); + KnownOne2 = APInt(BitWidth, 0); + // Recurse, but cap the recursion to one level, because we don't + // want to waste time spinning around in loops. + ComputeMaskedBits(P->getIncomingValue(i), KnownZero | KnownOne, + KnownZero2, KnownOne2, TD, MaxDepth-1); + KnownZero &= KnownZero2; + KnownOne &= KnownOne2; + // If all bits have been ruled out, there's no need to check + // more operands. + if (!KnownZero && !KnownOne) + break; + } + } break; } case Instruction::Call: |