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[EarlyCSE] Allow forwarding a non-invariant load into an invariant load. 

Reviewers: sanjoy

Subscribers: mcrosier, llvm-commits

Differential Revision: https://reviews.llvm.org/D23935

llvm-svn: 280265
This commit is contained in:
Geoff Berry 2016-08-31 17:45:31 +00:00
parent c7f76104b3
commit 64f5ed172a
2 changed files with 8 additions and 12 deletions
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10
llvm/lib/Transforms/Scalar/EarlyCSE.cpp
View File

@ -644,13 +644,13 @@ bool EarlyCSE::processNode(DomTreeNode *Node) {
// generation or the load is known to be from an invariant location,
// replace this instruction.
//
// A dominating invariant load implies that the location loaded from is
// unchanging beginning at the point of the invariant load, so the load
// we're CSE'ing _away_ does not need to be invariant, only the available
// load we're CSE'ing _to_ does.
// If either the dominating load or the current load are invariant, then
// we can assume the current load loads the same value as the dominating
// load.
LoadValue InVal = AvailableLoads.lookup(MemInst.getPointerOperand());
if (InVal.DefInst != nullptr &&
(InVal.Generation == CurrentGeneration || InVal.IsInvariant) &&
(InVal.Generation == CurrentGeneration ||
InVal.IsInvariant || MemInst.isInvariantLoad()) &&
InVal.MatchingId == MemInst.getMatchingId() &&
// We don't yet handle removing loads with ordering of any kind.
!MemInst.isVolatile() && MemInst.isUnordered() &&

10
llvm/test/Transforms/EarlyCSE/invariant-loads.ll
View File

@ -20,9 +20,7 @@ define void @f_0(i32* %ptr) {
}
define void @f_1(i32* %ptr) {
; We can forward invariant loads to non-invariant loads, since once an
; invariant load has executed, the location loaded from is known to be
; unchanging.
; We can forward invariant loads to non-invariant loads.
; CHECK-LABEL: @f_1(
; CHECK: %val0 = load i32, i32* %ptr, !invariant.load !0
@ -37,14 +35,12 @@ define void @f_1(i32* %ptr) {
}
define void @f_2(i32* %ptr) {
; Negative test -- we can't forward a non-invariant load into an
; invariant load.
; We can forward a non-invariant load into an invariant load.
; CHECK-LABEL: @f_2(
; CHECK: %val0 = load i32, i32* %ptr
; CHECK: call void @clobber_and_use(i32 %val0)
; CHECK: %val1 = load i32, i32* %ptr, !invariant.load !0
; CHECK: call void @clobber_and_use(i32 %val1)
; CHECK: call void @clobber_and_use(i32 %val0)
%val0 = load i32, i32* %ptr
call void @clobber_and_use(i32 %val0)