[EarlyCSE] Make PhiToCheck in removeMSSA() a set.

This way we end up not looking at PHI args already removed.
MemSSA now goes through the updater so we can prune
it to avoid having redundant MemoryPHI arguments, but that
doesn't quite work for the general case.

Discussed with Daniel Berlin, fixes PR33406.

llvm-svn: 305409

2 files changed, 29 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
index c4f450949e6..0f92760a874 100644
--- a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
+++ b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -15,6 +15,7 @@
 #include "llvm/Transforms/Scalar/EarlyCSE.h"
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/ScopedHashTable.h"
+#include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/GlobalsModRef.h"
@@ -506,7 +507,7 @@ private:
     if (MemoryAccess *MA = MSSA->getMemoryAccess(Inst)) {
       // Optimize MemoryPhi nodes that may become redundant by having all the
       // same input values once MA is removed.
-      SmallVector<MemoryPhi *, 4> PhisToCheck;
+      SmallSetVector<MemoryPhi *, 4> PhisToCheck;
       SmallVector<MemoryAccess *, 8> WorkQueue;
       WorkQueue.push_back(MA);
       // Process MemoryPhi nodes in FIFO order using a ever-growing vector since
@@ -517,7 +518,7 @@ private:
 
         for (auto *U : WI->users())
           if (MemoryPhi *MP = dyn_cast<MemoryPhi>(U))
-            PhisToCheck.push_back(MP);
+            PhisToCheck.insert(MP);
 
         MSSAUpdater->removeMemoryAccess(WI);
 
diff --git a/llvm/test/Transforms/EarlyCSE/pr33406.ll b/llvm/test/Transforms/EarlyCSE/pr33406.ll
new file mode 100644
index 00000000000..4d3312e1f0a
--- /dev/null
+++ b/llvm/test/Transforms/EarlyCSE/pr33406.ll
@@ -0,0 +1,26 @@
+; RUN: opt -early-cse-memssa -S %s | FileCheck %s
+
+; CHECK: define void @patatino() {
+; CHECK:  for.cond:
+; CHECK-NEXT:  br i1 true, label %if.end, label %for.inc
+; CHECK:  if.end:
+; CHECK-NEXT:  %tinkywinky = load i32, i32* @b
+; CHECK-NEXT:  br i1 true, label %for.inc, label %for.inc
+; CHECK:  for.inc:
+; CHECK-NEXT:  ret void
+
+
+@b = external global i32
+
+define void @patatino() {
+for.cond:
+  br i1 true, label %if.end, label %for.inc
+
+if.end:
+  %tinkywinky = load i32, i32* @b
+  store i32 %tinkywinky, i32* @b
+  br i1 true, label %for.inc, label %for.inc
+
+for.inc:
+  ret void
+}