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[MemorySSA] Update Phi simplification. 

When simplifying a Phi to the unique value found incoming, check that
there wasn't a Phi already created to break a cycle. If so, remove it.
Resolves PR43541.

Some additional nits included.

llvm-svn: 374471
This commit is contained in:
Alina Sbirlea 2019-10-10 23:27:21 +00:00
parent 1ccb39bbd8
commit 6442b56974
2 changed files with 62 additions and 5 deletions
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17
llvm/lib/Analysis/MemorySSAUpdater.cpp
View File

@ -44,15 +44,15 @@ MemoryAccess *MemorySSAUpdater::getPreviousDefRecursive(
// First, do a cache lookup. Without this cache, certain CFG structures
// (like a series of if statements) take exponential time to visit.
auto Cached = CachedPreviousDef.find(BB);
if (Cached != CachedPreviousDef.end()) {
if (Cached != CachedPreviousDef.end())
return Cached->second;
}
// If this method is called from an unreachable block, return LoE.
if (!MSSA->DT->isReachableFromEntry(BB))
return MSSA->getLiveOnEntryDef();
if (BasicBlock *Pred = BB->getSinglePredecessor()) {
if (BasicBlock *Pred = BB->getUniquePredecessor()) {
VisitedBlocks.insert(BB);
// Single predecessor case, just recurse, we can only have one definition.
MemoryAccess *Result = getPreviousDefFromEnd(Pred, CachedPreviousDef);
CachedPreviousDef.insert({BB, Result});
@ -96,9 +96,15 @@ MemoryAccess *MemorySSAUpdater::getPreviousDefRecursive(
// See if we can avoid the phi by simplifying it.
auto *Result = tryRemoveTrivialPhi(Phi, PhiOps);
// If we couldn't simplify, we may have to create a phi
if (Result == Phi && UniqueIncomingAccess && SingleAccess)
if (Result == Phi && UniqueIncomingAccess && SingleAccess) {
// A concrete Phi only exists if we created an empty one to break a cycle.
if (Phi) {
assert(Phi->operands().empty() && "Expected empty Phi");
Phi->replaceAllUsesWith(SingleAccess);
removeMemoryAccess(Phi);
}
Result = SingleAccess;
else if (Result == Phi && !(UniqueIncomingAccess && SingleAccess)) {
} else if (Result == Phi && !(UniqueIncomingAccess && SingleAccess)) {
if (!Phi)
Phi = MSSA->createMemoryPhi(BB);
@ -237,6 +243,7 @@ MemoryAccess *MemorySSAUpdater::tryRemoveTrivialPhi(MemoryPhi *Phi,
void MemorySSAUpdater::insertUse(MemoryUse *MU, bool RenameUses) {
InsertedPHIs.clear();
MU->setDefiningAccess(getPreviousDef(MU));
// In cases without unreachable blocks, because uses do not create new
// may-defs, there are only two cases:
// 1. There was a def already below us, and therefore, we should not have

50
llvm/test/Analysis/MemorySSA/pr43541.ll Normal file
View File

@ -0,0 +1,50 @@
; RUN: opt -gvn-hoist -enable-mssa-loop-dependency -S < %s | FileCheck %s
; REQUIRES: asserts
%struct.job_pool.6.7 = type { i32 }
; CHECK-LABEL: @f()
define dso_local void @f() {
entry:
br label %for.cond
for.cond: ; preds = %for.end, %entry
br label %for.body
for.body: ; preds = %for.cond
br label %if.end
if.then: ; No predecessors!
br label %if.end
if.end: ; preds = %if.then, %for.body
br i1 false, label %for.body12.lr.ph, label %for.end
for.body12.lr.ph: ; preds = %if.end
br label %for.body12
for.body12: ; preds = %if.end40, %for.body12.lr.ph
br label %if.then23
if.then23: ; preds = %for.body12
br i1 undef, label %if.then24, label %if.else
if.then24: ; preds = %if.then23
%0 = load %struct.job_pool.6.7*, %struct.job_pool.6.7** undef, align 8
br label %if.end40
if.else: ; preds = %if.then23
%1 = load %struct.job_pool.6.7*, %struct.job_pool.6.7** undef, align 8
br label %if.end40
if.end40: ; preds = %if.else, %if.then24
br i1 false, label %for.body12, label %for.cond9.for.end_crit_edge
for.cond9.for.end_crit_edge: ; preds = %if.end40
br label %for.end
for.end: ; preds = %for.cond9.for.end_crit_edge, %if.end
br i1 true, label %if.then45, label %for.cond
if.then45: ; preds = %for.end
ret void
}