From 05cd88656135255b545d24adb51c2ba1b5c8b99e Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Mon, 23 May 2011 00:21:50 +0000 Subject: Transform any logical shift of a power of two into an exact/NUW shift when in a known-non-zero context. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131887 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/InstCombine/InstCombineMulDivRem.cpp | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) (limited to 'lib/Transforms/InstCombine/InstCombineMulDivRem.cpp') diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp index fdec6407b8..f3d10611ad 100644 --- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp +++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp @@ -29,6 +29,23 @@ static Value *simplifyValueKnownNonZero(Value *V, InstCombiner &IC) { // code. if (!V->hasOneUse()) return 0; + + // (PowerOfTwo >>u B) --> isExact since shifting out the result would make it + // inexact. Similarly for <<. + if (BinaryOperator *I = dyn_cast(V)) + if (I->isLogicalShift() && + isPowerOfTwo(I->getOperand(0), IC.getTargetData())) { + if (I->getOpcode() == Instruction::LShr && !I->isExact()) { + I->setIsExact(); + return I; + } + + if (I->getOpcode() == Instruction::Shl && !I->hasNoUnsignedWrap()) { + I->setHasNoUnsignedWrap(); + return I; + } + } + // ((1 << A) >>u B) --> (1 << (A-B)) // Because V cannot be zero, we know that B is less than A. Value *A = 0, *B = 0, *PowerOf2 = 0; -- cgit v1.2.3-18-g5258