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author | Dan Gohman <gohman@apple.com> | 2009-02-24 02:00:40 +0000 |
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committer | Dan Gohman <gohman@apple.com> | 2009-02-24 02:00:40 +0000 |
commit | 0001e56f15215ae4bc5fffb82eec5c4828b888f0 (patch) | |
tree | c14953e84d899048fdcd5828b6b2b4ecac2ccb2a | |
parent | c34fea3935dcc0cab13cfb5cb60471bd49089230 (diff) | |
download | llvm-0001e56f15215ae4bc5fffb82eec5c4828b888f0.tar.gz llvm-0001e56f15215ae4bc5fffb82eec5c4828b888f0.tar.bz2 llvm-0001e56f15215ae4bc5fffb82eec5c4828b888f0.tar.xz |
Fix a ValueTracking rule: RHS means operand 1, not 0. Add a simple
ashr instcombine to help expose this code. And apply the fix to
SelectionDAG's copy of this code too.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@65364 91177308-0d34-0410-b5e6-96231b3b80d8
-rw-r--r-- | lib/Analysis/ValueTracking.cpp | 2 | ||||
-rw-r--r-- | lib/CodeGen/SelectionDAG/SelectionDAG.cpp | 2 | ||||
-rw-r--r-- | lib/Transforms/Scalar/InstructionCombining.cpp | 7 | ||||
-rw-r--r-- | test/Transforms/InstCombine/ashr-nop.ll | 8 |
4 files changed, 16 insertions, 3 deletions
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp index 7ac138b90e..20fa69ea24 100644 --- a/lib/Analysis/ValueTracking.cpp +++ b/lib/Analysis/ValueTracking.cpp @@ -625,7 +625,7 @@ unsigned llvm::ComputeNumSignBits(Value *V, TargetData *TD, unsigned Depth) { if (Tmp == 1) return 1; // Early out. // Special case decrementing a value (ADD X, -1): - if (ConstantInt *CRHS = dyn_cast<ConstantInt>(U->getOperand(0))) + if (ConstantInt *CRHS = dyn_cast<ConstantInt>(U->getOperand(1))) if (CRHS->isAllOnesValue()) { APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); APInt Mask = APInt::getAllOnesValue(TyBits); diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp index 66356f5f9a..358c9703a8 100644 --- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp +++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp @@ -2008,7 +2008,7 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, unsigned Depth) const{ if (Tmp == 1) return 1; // Early out. // Special case decrementing a value (ADD X, -1): - if (ConstantSDNode *CRHS = dyn_cast<ConstantSDNode>(Op.getOperand(0))) + if (ConstantSDNode *CRHS = dyn_cast<ConstantSDNode>(Op.getOperand(1))) if (CRHS->isAllOnesValue()) { APInt KnownZero, KnownOne; APInt Mask = APInt::getAllOnesValue(VTBits); diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index 7f2cab96ec..62554a5e91 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -7031,7 +7031,12 @@ Instruction *InstCombiner::visitAShr(BinaryOperator &I) { MaskedValueIsZero(Op0, APInt::getSignBit(I.getType()->getPrimitiveSizeInBits()))) return BinaryOperator::CreateLShr(Op0, I.getOperand(1)); - + + // Arithmetic shifting an all-sign-bit value is a no-op. + unsigned NumSignBits = ComputeNumSignBits(Op0); + if (NumSignBits == Op0->getType()->getPrimitiveSizeInBits()) + return ReplaceInstUsesWith(I, Op0); + return 0; } diff --git a/test/Transforms/InstCombine/ashr-nop.ll b/test/Transforms/InstCombine/ashr-nop.ll new file mode 100644 index 0000000000..bb0da346b0 --- /dev/null +++ b/test/Transforms/InstCombine/ashr-nop.ll @@ -0,0 +1,8 @@ +; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep ashr + +define i32 @foo(i32 %x) { + %o = and i32 %x, 1 + %n = add i32 %o, -1 + %t = ashr i32 %n, 17 + ret i32 %t +} |