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[ARM] Handle all-ones mask explicitly in targetShrinkDemandedConstant.

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This avoids a potential infinite loop setting and unsetting bits in the
mask.

Reduced from a failure on the polly-aosp bot.

Differential Revision: https://reviews.llvm.org/D51066

llvm-svn: 340446
This commit is contained in:
Eli Friedman 2018-08-22 20:13:45 +00:00
parent facf6eb783
commit c4518513f4
2 changed files with 46 additions and 4 deletions
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15
lib/Target/ARM/ARMISelLowering.cpp
View File

@ -13647,14 +13647,21 @@ ARMTargetLowering::targetShrinkDemandedConstant(SDValue Op,
unsigned Mask = C->getZExtValue();
// If mask is zero, nothing to do.
if (!Mask)
return false;
unsigned Demanded = DemandedAPInt.getZExtValue();
unsigned ShrunkMask = Mask & Demanded;
unsigned ExpandedMask = Mask | ~Demanded;
// If the mask is all zeros, let the target-independent code replace the
// result with zero.
if (ShrunkMask == 0)
return false;
// If the mask is all ones, erase the AND. (Currently, the target-independent
// code won't do this, so we have to do it explicitly to avoid an infinite
// loop in obscure cases.)
if (ExpandedMask == ~0U)
return TLO.CombineTo(Op, Op.getOperand(0));
auto IsLegalMask = [ShrunkMask, ExpandedMask](unsigned Mask) -> bool {
return (ShrunkMask & Mask) == ShrunkMask && (~ExpandedMask & Mask) == 0;
};

35
test/CodeGen/ARM/demanded-bits-and.ll Normal file
View File

@ -0,0 +1,35 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
; RUN: llc -mtriple=arm-eabi < %s | FileCheck %s
; Make sure this doesn't hang, and there are no unnecessary
; "and" instructions.
define dso_local void @f(i16* %p) {
; CHECK-LABEL: f:
; CHECK: @ %bb.0: @ %entry
; CHECK-NEXT: .LBB0_1: @ %bb
; CHECK-NEXT: @ =>This Inner Loop Header: Depth=1
; CHECK-NEXT: ldrh r1, [r0]
; CHECK-NEXT: and r2, r1, #255
; CHECK-NEXT: add r3, r2, r1, lsr #8
; CHECK-NEXT: add r2, r3, r2
; CHECK-NEXT: add r1, r2, r1, lsr #8
; CHECK-NEXT: add r1, r1, #2
; CHECK-NEXT: lsr r1, r1, #2
; CHECK-NEXT: strh r1, [r0]
; CHECK-NEXT: b .LBB0_1
entry:
br label %bb
bb:
%_p_scalar_ = load i16, i16* %p, align 2
%p_and = and i16 %_p_scalar_, 255
%p_ = lshr i16 %_p_scalar_, 8
%p_add = add nuw nsw i16 %p_, 2
%p_add14 = add nuw nsw i16 %p_add, %p_and
%p_add18 = add nuw nsw i16 %p_add14, %p_and
%p_add19 = add nuw nsw i16 %p_add18, %p_
%p_200 = lshr i16 %p_add19, 2
store i16 %p_200, i16* %p, align 2
br label %bb
}