From 5ff30e70f8dc4ddfdb3bd6925ccdf524130a7b95 Mon Sep 17 00:00:00 2001 From: Duncan Sands Date: Mon, 30 Apr 2012 11:56:58 +0000 Subject: [PATCH] Just mark the sign bit as known zero, rather than any other irrelevant bits known zero in the LHS. Fixes PR12541. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155818 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Analysis/ValueTracking.cpp | 2 +- test/Transforms/InstCombine/2012-04-30-SRem.ll | 12 ++++++++++++ 2 files changed, 13 insertions(+), 1 deletion(-) create mode 100644 test/Transforms/InstCombine/2012-04-30-SRem.ll diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp index a430f6281ef..1418e01d7c8 100644 --- a/lib/Analysis/ValueTracking.cpp +++ b/lib/Analysis/ValueTracking.cpp @@ -564,7 +564,7 @@ void llvm::ComputeMaskedBits(Value *V, APInt &KnownZero, APInt &KnownOne, Depth+1); // If it's known zero, our sign bit is also zero. if (LHSKnownZero.isNegative()) - KnownZero |= LHSKnownZero; + KnownZero.setBit(BitWidth - 1); } break; diff --git a/test/Transforms/InstCombine/2012-04-30-SRem.ll b/test/Transforms/InstCombine/2012-04-30-SRem.ll new file mode 100644 index 00000000000..a285d5aea5e --- /dev/null +++ b/test/Transforms/InstCombine/2012-04-30-SRem.ll @@ -0,0 +1,12 @@ +; RUN: opt -instcombine -S < %s | FileCheck %s +; PR12541 + +define i32 @foo(i32 %x) { + %y = xor i32 %x, 3 + %z = srem i32 1656690544, %y + %sext = shl i32 %z, 24 + %s = ashr exact i32 %sext, 24 + ret i32 %s +; CHECK-NOT: and +; The shifts were wrongly being turned into an and with 112 +}