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[DAG] Fix and-mask folding when narrowing loads. 

Summary:
Check that and masks are strictly smaller than implicit mask from
narrowed load.

Fixes PR37820.

Reviewers: samparker, RKSimon, nemanjai

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D48335

llvm-svn: 335137
This commit is contained in:
Nirav Dave 2018-06-20 15:36:29 +00:00
parent da873b5e2e
commit cd558887d3
2 changed files with 28 additions and 2 deletions
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5
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -8688,8 +8688,9 @@ SDValue DAGCombiner::ReduceLoadWidth(SDNode *N) {
if (ShiftMask.isMask()) {
EVT MaskedVT = EVT::getIntegerVT(*DAG.getContext(),
ShiftMask.countTrailingOnes());
// Recompute the type.
if (TLI.isLoadExtLegal(ExtType, N0.getValueType(), MaskedVT))
// If the mask is smaller, recompute the type.
if ((ExtVT.getSizeInBits() > MaskedVT.getSizeInBits()) &&
TLI.isLoadExtLegal(ExtType, N0.getValueType(), MaskedVT))
ExtVT = MaskedVT;
}
}

25
llvm/test/CodeGen/X86/pr37820.ll Normal file
View File

@ -0,0 +1,25 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
; RUN: llc -mtriple=x86_64-unknown-linux-gnu %s -o - | FileCheck %s
@a = external dso_local local_unnamed_addr global i64, align 8
@c = external dso_local local_unnamed_addr global i64, align 8
@b = external dso_local local_unnamed_addr global i64, align 8
; Should generate a 16-bit load
define void @foo() {
; CHECK-LABEL: foo:
; CHECK: # %bb.0: # %entry
; CHECK-NEXT: movzwl a+{{.*}}(%rip), %eax
; CHECK-NEXT: movq %rax, {{.*}}(%rip)
; CHECK-NEXT: retq
entry:
%0 = load i64, i64* @a, align 8
%1 = load i64, i64* @c, align 8
%and = and i64 %1, -16384
%add = add nsw i64 %and, 4503359447364223024
%shr = lshr i64 %0, %add
%conv1 = and i64 %shr, 4294967295
store i64 %conv1, i64* @b, align 8
ret void
}