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[AST] Mark invariant.starts as being readonly

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These intrinsics are modelled as writing for control flow purposes, but they don't actually write to any location. Marking these - as we did for guards - allows LICM to hoist loads out of loops containing invariant.starts.

Differential Revision: https://reviews.llvm.org/D50861

llvm-svn: 340245
This commit is contained in:
Philip Reames 2018-08-21 00:55:35 +00:00
parent 261daa0f69
commit cca970de48
2 changed files with 6 additions and 6 deletions
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3
lib/Analysis/AliasSetTracker.cpp
View File

@ -174,7 +174,8 @@ void AliasSet::addUnknownInst(Instruction *I, AliasAnalysis &AA) {
// but don't actually modify any specific memory location.
using namespace PatternMatch;
bool MayWriteMemory = I->mayWriteToMemory() &&
!match(I, m_Intrinsic<Intrinsic::experimental_guard>());
!match(I, m_Intrinsic<Intrinsic::experimental_guard>()) &&
!(I->use_empty() && match(I, m_Intrinsic<Intrinsic::invariant_start>()));
if (!MayWriteMemory) {
Alias = SetMayAlias;
Access |= RefAccess;

9
test/Transforms/LICM/invariant.start.ll
View File

@ -7,9 +7,9 @@
define void @test1(i1 %cond, i32* %ptr) {
; CHECK-LABEL: @test1(
; CHECK-LABEL: entry:
; CHECK: %val = load i32, i32* %ptr
; CHECK-LABEL: loop:
; CHECK: call {}* @llvm.invariant.start.p0i32(i64 4, i32* %ptr)
; CHECK: %val = load i32, i32* %ptr
; ALIAS-N2-LABEL: @test1(
; ALIAS-N2-LABEL: entry:
@ -28,14 +28,14 @@ loop:
br label %loop
}
;; TODO: By default, despite the loop varying invariant.start, we should be
;; despite the loop varying invariant.start, we should be
;; able to hoist the load
define void @test2(i1 %cond, i32* %ptr) {
; CHECK-LABEL: @test2(
; CHECK-LABEL: entry:
; CHECK: %val = load i32, i32* %ptr
; CHECK-LABEL: loop:
; CHECK: call {}* @llvm.invariant.start.p0i32(i64 4, i32* %piv)
; CHECK: %val = load i32, i32* %ptr
; ALIAS-N2-LABEL: @test2(
; ALIAS-N2-LABEL: entry:
@ -54,13 +54,12 @@ loop:
br label %loop
}
; By default, should be able to hoist since store doesn't alias
define void @test3(i1 %cond, i32* %ptr) {
; CHECK-LABEL: @test3(
; CHECK-LABEL: entry:
; CHECK: %val = load i32, i32* %ptr
; CHECK-LABEL: loop:
; CHECK: call {}* @llvm.invariant.start.p0i32(i64 4, i32* %ptr)
; CHECK: %val = load i32, i32* %ptr
; ALIAS-N2-LABEL: @test3(
; ALIAS-N2-LABEL: entry: