1 files changed, 17 insertions, 7 deletions

diff --git a/lib/Transforms/Utils/SimplifyInstructions.cpp b/lib/Transforms/Utils/SimplifyInstructions.cpp
index bbd65f1..33b3637 100644
--- a/lib/Transforms/Utils/SimplifyInstructions.cpp
+++ b/lib/Transforms/Utils/SimplifyInstructions.cpp
@@ -14,7 +14,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#define DEBUG_TYPE "instsimplify"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/ADT/DepthFirstIterator.h"
 #include "llvm/ADT/SmallPtrSet.h"
@@ -29,6 +28,8 @@
 #include "llvm/Transforms/Utils/Local.h"
 using namespace llvm;
 
+#define DEBUG_TYPE "instsimplify"
+
 STATISTIC(NumSimplified, "Number of redundant instructions removed");
 
 namespace {
@@ -47,17 +48,18 @@ namespace {
     bool runOnFunction(Function &F) override {
       const DominatorTreeWrapperPass *DTWP =
           getAnalysisIfAvailable<DominatorTreeWrapperPass>();
-      const DominatorTree *DT = DTWP ? &DTWP->getDomTree() : 0;
+      const DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
       DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
-      const DataLayout *DL = DLP ? &DLP->getDataLayout() : 0;
+      const DataLayout *DL = DLP ? &DLP->getDataLayout() : nullptr;
       const TargetLibraryInfo *TLI = &getAnalysis<TargetLibraryInfo>();
       SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
       bool Changed = false;
 
       do {
-        for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
-             DE = df_end(&F.getEntryBlock()); DI != DE; ++DI)
-          for (BasicBlock::iterator BI = DI->begin(), BE = DI->end(); BI != BE;) {
+        for (BasicBlock *BB : depth_first(&F.getEntryBlock()))
+          // Here be subtlety: the iterator must be incremented before the loop
+          // body (not sure why), so a range-for loop won't work here.
+          for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
             Instruction *I = BI++;
             // The first time through the loop ToSimplify is empty and we try to
             // simplify all instructions.  On later iterations ToSimplify is not
@@ -74,7 +76,15 @@ namespace {
                 ++NumSimplified;
                 Changed = true;
               }
-            Changed |= RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
+            bool res = RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
+            if (res)  {
+              // RecursivelyDeleteTriviallyDeadInstruction can remove
+              // more than one instruction, so simply incrementing the
+              // iterator does not work. When instructions get deleted
+              // re-iterate instead.
+              BI = BB->begin(); BE = BB->end();
+              Changed |= res;
+            }
           }
 
         // Place the list of instructions to simplify on the next loop iteration