[JumpThreading] Don't forget to report that the IR changed

JumpThreading's runOnFunction is supposed to return true if it made any
changes.  JumpThreading has a call to removeUnreachableBlocks which may
result in changes to the IR but runOnFunction didn't appropriate account
for this possibility, leading to badness.

While we are here, make sure to call LazyValueInfo::eraseBlock in
removeUnreachableBlocks;  JumpThreading preserves LVI.

This fixes PR26096.

llvm-svn: 257279

2 files changed, 7 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 35a10db3292..dcdcfed66e6 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -211,11 +211,12 @@ bool JumpThreading::runOnFunction(Function &F) {
   // we will loop forever. We take care of this issue by not jump threading for
   // back edges. This works for normal cases but not for unreachable blocks as
   // they may have cycle with no back edge.
-  removeUnreachableBlocks(F);
+  bool EverChanged = false;
+  EverChanged |= removeUnreachableBlocks(F, LVI);
 
   FindLoopHeaders(F);
 
-  bool Changed, EverChanged = false;
+  bool Changed;
   do {
     Changed = false;
     for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 0e386ac83e9..e4310c79736 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -23,6 +23,7 @@
 #include "llvm/Analysis/EHPersonalities.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/MemoryBuiltins.h"
+#include "llvm/Analysis/LazyValueInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/Constants.h"
@@ -1407,7 +1408,7 @@ void llvm::removeUnwindEdge(BasicBlock *BB) {
 /// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
 /// if they are in a dead cycle.  Return true if a change was made, false
 /// otherwise.
-bool llvm::removeUnreachableBlocks(Function &F) {
+bool llvm::removeUnreachableBlocks(Function &F, LazyValueInfo *LVI) {
   SmallPtrSet<BasicBlock*, 128> Reachable;
   bool Changed = markAliveBlocks(F, Reachable);
 
@@ -1428,6 +1429,8 @@ bool llvm::removeUnreachableBlocks(Function &F) {
          ++SI)
       if (Reachable.count(*SI))
         (*SI)->removePredecessor(&*BB);
+    if (LVI)
+      LVI->eraseBlock(&*BB);
     BB->dropAllReferences();
   }