[llvm] 1882568 - [BasicAA] Only add visited phi blocks temporarily

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2020-10-22T22:26:29+02:00
New Revision: 1882568fcb08ed8af689f13826cc7e84c3c84e33

URL: https://github.com/llvm/llvm-project/commit/1882568fcb08ed8af689f13826cc7e84c3c84e33
DIFF: https://github.com/llvm/llvm-project/commit/1882568fcb08ed8af689f13826cc7e84c3c84e33.diff

LOG: [BasicAA] Only add visited phi blocks temporarily

Visited phi blocks only need to be added for the duration of the
recursive alias queries, they should not leak into following code.

Once again, while this also improves analysis precision, this is
mainly intended to clarify the applicability scope of VisitedPhiBBs.

Added: 
    

Modified: 
    llvm/lib/Analysis/BasicAliasAnalysis.cpp
    llvm/test/Analysis/BasicAA/phi-aa.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 3e1adaf84f6f..30de50dc3c88 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -14,6 +14,7 @@
 
 #include "llvm/Analysis/BasicAliasAnalysis.h"
 #include "llvm/ADT/APInt.h"
+#include "llvm/ADT/ScopeExit.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
@@ -814,7 +815,7 @@ AliasResult BasicAAResult::alias(const MemoryLocation &LocA,
   AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.AATags, LocB.Ptr,
                                  LocB.Size, LocB.AATags, AAQI);
 
-  VisitedPhiBBs.clear();
+  assert(VisitedPhiBBs.empty());
   return Alias;
 }
 
@@ -1654,7 +1655,11 @@ AliasResult BasicAAResult::aliasPHI(const PHINode *PN, LocationSize PNSize,
   // In the recursive alias queries below, we may compare values from two
   // 
diff erent loop iterations. Keep track of visited phi blocks, which will
   // be used when determining value equivalence.
-  VisitedPhiBBs.insert(PN->getParent());
+  auto Pair = VisitedPhiBBs.insert(PN->getParent());
+  auto _ = make_scope_exit([&]() {
+    if (Pair.second)
+      VisitedPhiBBs.erase(PN->getParent());
+  });
 
   AliasResult Alias = aliasCheck(V2, V2Size, V2AAInfo, V1Srcs[0], PNSize,
                                  PNAAInfo, AAQI, UnderV2);

diff  --git a/llvm/test/Analysis/BasicAA/phi-aa.ll b/llvm/test/Analysis/BasicAA/phi-aa.ll
index 299dc01e7e90..aa2e078000a7 100644
--- a/llvm/test/Analysis/BasicAA/phi-aa.ll
+++ b/llvm/test/Analysis/BasicAA/phi-aa.ll
@@ -116,7 +116,7 @@ end:
 }
 
 ; CHECK-LABEL: phi_and_select
-; CHECK: MayAlias: i32* %p, i32* %s
+; CHECK: MustAlias: i32* %p, i32* %s
 define void @phi_and_select(i1 %c, i1 %c2, i32* %x, i32* %y) {
 entry:
   br i1 %c, label %true, label %false