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author | Sanjay Patel <spatel@rotateright.com> | 2017-01-30 16:53:03 +0000 |
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committer | Sanjay Patel <spatel@rotateright.com> | 2017-01-30 16:53:03 +0000 |
commit | 8e644c08ee6e921430e1a1f3e9a8b9dab6c0f8f9 (patch) | |
tree | c1f9cd5f048efeda94fb0389463cf09da54712eb /llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp | |
parent | 5d6687da99d945f4b0b1e020b6583515dca530cc (diff) | |
download | bcm5719-llvm-8e644c08ee6e921430e1a1f3e9a8b9dab6c0f8f9.tar.gz bcm5719-llvm-8e644c08ee6e921430e1a1f3e9a8b9dab6c0f8f9.zip |
[InstCombine] fixed to propagate 'exact' on lshr
The original shift is bigger, so this may qualify as 'obvious',
but here's an attempt at an Alive-based proof:
Name: exact
Pre: (C1 u< C2)
%a = shl i8 %x, C1
%b = lshr exact i8 %a, C2
=>
%c = lshr exact i8 %x, C2 - C1
%b = and i8 %c, ((1 << width(C1)) - 1) u>> C2
Optimization is correct!
llvm-svn: 293498
Diffstat (limited to 'llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp')
-rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp index 6cf64c26172..55b37f0fe62 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp @@ -773,7 +773,7 @@ Instruction *InstCombiner::visitLShr(BinaryOperator &I) { return NewLShr; } // (X << C1) >>u C2 --> (X >>u (C2 - C1)) & (-1 >> C2) - Value *NewLShr = Builder->CreateLShr(X, ShiftDiff); + Value *NewLShr = Builder->CreateLShr(X, ShiftDiff, "", I.isExact()); APInt Mask(APInt::getLowBitsSet(BitWidth, BitWidth - ShAmt)); return BinaryOperator::CreateAnd(NewLShr, ConstantInt::get(Ty, Mask)); } |