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| author | Eli Friedman <eli.friedman@gmail.com> | 2010-01-31 02:30:23 +0000 |
|---|---|---|
| committer | Eli Friedman <eli.friedman@gmail.com> | 2010-01-31 02:30:23 +0000 |
| commit | 694488f4770468f03b974180631c0fbfa21b28cc (patch) | |
| tree | ff3af0445dfed3464a6c36bf37a5f8736a12097e | |
| parent | 894c1af05fb3f0d8e2ee6565816fa220b260ed9d (diff) | |
| download | llvm-694488f4770468f03b974180631c0fbfa21b28cc.tar.gz llvm-694488f4770468f03b974180631c0fbfa21b28cc.tar.bz2 llvm-694488f4770468f03b974180631c0fbfa21b28cc.tar.xz | |
Add a small transform: transform -(X<<Y) to (-X<<Y) when the shift has a single
use and X is free to negate.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94941 91177308-0d34-0410-b5e6-96231b3b80d8
| -rw-r--r-- | lib/Transforms/InstCombine/InstCombineAddSub.cpp | 7 | ||||
| -rw-r--r-- | test/Transforms/InstCombine/sub.ll | 8 |
2 files changed, 15 insertions, 0 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp index 4891ff00e7..119b1cad63 100644 --- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp +++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp @@ -676,6 +676,13 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) { return BinaryOperator::CreateSDiv(Op1I->getOperand(0), ConstantExpr::getNeg(DivRHS)); + // 0 - (C << X) -> (-C << X) + if (Op1I->getOpcode() == Instruction::Shl) + if (ConstantInt *CSI = dyn_cast<ConstantInt>(Op0)) + if (CSI->isZero()) + if (Value *ShlLHSNeg = dyn_castNegVal(Op1I->getOperand(0))) + return BinaryOperator::CreateShl(ShlLHSNeg, Op1I->getOperand(1)); + // X - X*C --> X * (1-C) ConstantInt *C2 = 0; if (dyn_castFoldableMul(Op1I, C2) == Op0) { diff --git a/test/Transforms/InstCombine/sub.ll b/test/Transforms/InstCombine/sub.ll index fa0322a44e..29bd7be2ff 100644 --- a/test/Transforms/InstCombine/sub.ll +++ b/test/Transforms/InstCombine/sub.ll @@ -272,4 +272,12 @@ define i64 @test25(i8* %P, i64 %A){ ; CHECK-NEXT: ret i64 } +define i32 @test26(i32 %x) { + %shl = shl i32 3, %x + %neg = sub i32 0, %shl + ret i32 %neg +; CHECK: @test26 +; CHECK-NEXT: shl i32 -3 +; CHECK-NEXT: ret i32 +} |