Be more careful modifying the use_list while also iterating through it.

llvm-svn: 46417

2 files changed, 4 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopUnroll.cpp b/llvm/lib/Transforms/Scalar/LoopUnroll.cpp
index ff2168ac8de..b514156a1af 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnroll.cpp
@@ -365,8 +365,9 @@ bool LoopUnroll::unrollLoop(Loop *L, unsigned Count, unsigned Threshold) {
       // be updated specially after unrolling all the way.
       if (*BB != LatchBlock)
         for (Value::use_iterator UI = (*BB)->use_begin(), UE = (*BB)->use_end();
-             UI != UE; ++UI) {
+             UI != UE;) {
           Instruction *UseInst = cast<Instruction>(*UI);
+          ++UI;
           if (isa<PHINode>(UseInst) && !L->contains(UseInst->getParent())) {
             PHINode *phi = cast<PHINode>(UseInst);
             Value *Incoming = phi->getIncomingValueForBlock(*BB);
diff --git a/llvm/test/Transforms/LoopUnroll/2007-11-05-Crash.ll b/llvm/test/Transforms/LoopUnroll/2007-11-05-Crash.ll
index a5e13d5a26a..a46c09e3bde 100644
--- a/llvm/test/Transforms/LoopUnroll/2007-11-05-Crash.ll
+++ b/llvm/test/Transforms/LoopUnroll/2007-11-05-Crash.ll
@@ -1,5 +1,7 @@
 ; RUN: llvm-as < %s | opt -disable-output -loop-unroll
 ; PR1770
+; PR1947
+
 	%struct.cl_engine = type { i32, i16, i32, i8**, i8**, i8*, i8*, i8*, i8*, i8*, i8*, i8* }
 	%struct.cl_limits = type { i32, i32, i32, i32, i16, i64 }
 	%struct.cli_ac_alt = type { i8, i8*, i16, i16, %struct.cli_ac_alt* }