From fe66a6200ddb841fcf6aa7709ef752a5152cbffb Mon Sep 17 00:00:00 2001 From: James Molloy Date: Mon, 25 Jan 2016 14:49:36 +0000 Subject: [PATCH] [DemandedBits] Fix computation of demanded bits for ICmps The computation of ICmp demanded bits is independent of the individual operand being evaluated. We simply return a mask consisting of the minimum leading zeroes of both operands. We were incorrectly passing "I" to ComputeKnownBits - this should be "UserI->getOperand(0)". In cases where we were evaluating the 1th operand, we were taking the minimum leading zeroes of it and itself. This should fix PR26266. llvm-svn: 258690 --- lib/Analysis/DemandedBits.cpp | 2 +- test/Analysis/DemandedBits/basic.ll | 13 +++++++++++-- 2 files changed, 12 insertions(+), 3 deletions(-) diff --git a/lib/Analysis/DemandedBits.cpp b/lib/Analysis/DemandedBits.cpp index 912c5ceb754..143d0b79f18 100644 --- a/lib/Analysis/DemandedBits.cpp +++ b/lib/Analysis/DemandedBits.cpp @@ -244,7 +244,7 @@ void DemandedBits::determineLiveOperandBits( break; case Instruction::ICmp: // Count the number of leading zeroes in each operand. - ComputeKnownBits(BitWidth, I, UserI->getOperand(1)); + ComputeKnownBits(BitWidth, UserI->getOperand(0), UserI->getOperand(1)); auto NumLeadingZeroes = std::min(KnownZero.countLeadingOnes(), KnownZero2.countLeadingOnes()); AB = ~APInt::getHighBitsSet(BitWidth, NumLeadingZeroes); diff --git a/test/Analysis/DemandedBits/basic.ll b/test/Analysis/DemandedBits/basic.ll index 487e522e9db..9973edf79c1 100644 --- a/test/Analysis/DemandedBits/basic.ll +++ b/test/Analysis/DemandedBits/basic.ll @@ -24,11 +24,20 @@ define i1 @test_icmp1(i32 %a, i32 %b) { ; CHECK-LABEL: 'test_icmp2' ; CHECK-DAG: DemandedBits: 0x1 for %3 = icmp eq i32 %1, %2 -; CHECK-DAG: DemandedBits: 0xFF for %1 = and i32 %a, 255 -; CHECK-DAG: DemandedBits: 0xF for %2 = ashr i32 %1, 4 +; CHECK-DAG: DemandedBits: 0xFFF for %1 = and i32 %a, 255 +; CHECK-DAG: DemandedBits: 0xFF for %2 = ashr i32 %1, 4 define i1 @test_icmp2(i32 %a, i32 %b) { %1 = and i32 %a, 255 %2 = ashr i32 %1, 4 %3 = icmp eq i32 %1, %2 ret i1 %3 } + +; CHECK-LABEL: 'test_icmp3' +; CHECK-DAG: DemandedBits: 0xFFFFFFFF for %1 = and i32 %a, 255 +; CHECK-DAG: DemandedBits: 0x1 for %2 = icmp eq i32 -1, %1 +define i1 @test_icmp3(i32 %a) { + %1 = and i32 %a, 255 + %2 = icmp eq i32 -1, %1 + ret i1 %2 +}