From 648b20d5dbc54391f0d38c6ff16cf304bf3cb297 Mon Sep 17 00:00:00 2001 From: Owen Anderson Date: Mon, 1 Nov 2010 21:08:20 +0000 Subject: [PATCH] When folding away a (shl (shr)) pair, we need to check that the bits that will BECOME the low bits are zero, not that the current low bits are zero. Fixes . git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117953 91177308-0d34-0410-b5e6-96231b3b80d8 --- .../InstCombine/InstCombineShifts.cpp | 2 +- .../InstCombine/2010-11-01-lshr-mask.ll | 20 +++++++++++++++++++ 2 files changed, 21 insertions(+), 1 deletion(-) create mode 100644 test/Transforms/InstCombine/2010-11-01-lshr-mask.ll diff --git a/lib/Transforms/InstCombine/InstCombineShifts.cpp b/lib/Transforms/InstCombine/InstCombineShifts.cpp index 27716b886a2..012d238729a 100644 --- a/lib/Transforms/InstCombine/InstCombineShifts.cpp +++ b/lib/Transforms/InstCombine/InstCombineShifts.cpp @@ -157,7 +157,7 @@ static bool CanEvaluateShifted(Value *V, unsigned NumBits, bool isLeftShift, if (CI->getZExtValue() > NumBits) { unsigned LowBits = CI->getZExtValue() - NumBits; if (MaskedValueIsZero(I->getOperand(0), - APInt::getLowBitsSet(TypeWidth, LowBits))) + APInt::getLowBitsSet(TypeWidth, LowBits) << NumBits)) return true; } diff --git a/test/Transforms/InstCombine/2010-11-01-lshr-mask.ll b/test/Transforms/InstCombine/2010-11-01-lshr-mask.ll new file mode 100644 index 00000000000..d74c70e4f75 --- /dev/null +++ b/test/Transforms/InstCombine/2010-11-01-lshr-mask.ll @@ -0,0 +1,20 @@ +; RUN: opt -instcombine -S < %s | FileCheck %s +; + +define i32 @main(i32 %argc) nounwind ssp { +entry: + %tmp3151 = trunc i32 %argc to i8 + %tmp3161 = or i8 %tmp3151, -17 + %tmp3162 = and i8 %tmp3151, 122 + %tmp3163 = xor i8 %tmp3162, -17 + %tmp4114 = shl i8 %tmp3163, 6 + %tmp4115 = xor i8 %tmp4114, %tmp3163 + %tmp4120 = xor i8 %tmp3161, %tmp4115 +; CHECK: lshr i8 %tmp4115, 1 +; CHECK-NOT: shl i8 %tmp4126, 6 + %tmp4126 = lshr i8 %tmp4120, 7 + %tmp4127 = mul i8 %tmp4126, 64 + %tmp4086 = zext i8 %tmp4127 to i32 +; CHECK: ret i32 + ret i32 %tmp4086 +} -- 2.34.1