[llvm] r250922 - [SimplifyCFG] Don't use-after-free an SSA value

[David Majnemer via llvm-commits]

Author: majnemer
Date: Wed Oct 21 13:22:24 2015
New Revision: 250922

URL: http://llvm.org/viewvc/llvm-project?rev=250922&view=rev
Log:
[SimplifyCFG] Don't use-after-free an SSA value

SimplifyTerminatorOnSelect didn't consider the possibility that the
condition might be related to one of PHI nodes.

This fixes PR25267.

Added:
    llvm/trunk/test/Transforms/SimplifyCFG/PR25267.ll
Modified:
    llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp

Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=250922&r1=250921&r2=250922&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Wed Oct 21 13:22:24 2015
@@ -2571,7 +2571,8 @@ static bool SimplifyTerminatorOnSelect(T
     else if (Succ == KeepEdge2)
       KeepEdge2 = nullptr;
     else
-      Succ->removePredecessor(OldTerm->getParent());
+      Succ->removePredecessor(OldTerm->getParent(),
+                              /*DontDeleteUselessPHIs=*/true);
   }
 
   IRBuilder<> Builder(OldTerm);

Added: llvm/trunk/test/Transforms/SimplifyCFG/PR25267.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/PR25267.ll?rev=250922&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/PR25267.ll (added)
+++ llvm/trunk/test/Transforms/SimplifyCFG/PR25267.ll Wed Oct 21 13:22:24 2015
@@ -0,0 +1,24 @@
+; RUN: opt < %s -simplifycfg -S | FileCheck %s
+
+define void @f() {
+entry:
+  br label %for.cond
+
+for.cond:
+  %phi = phi i1 [ false, %entry ], [ true, %for.body ]
+  %select = select i1 %phi, i32 1, i32 2
+  br label %for.body
+
+for.body:
+  switch i32 %select, label %for.cond [
+    i32 1, label %return
+    i32 2, label %for.body
+  ]
+
+return:
+  ret void
+}
+
+; CHECK-LABEL: define void @f(
+; CHECK: br label %[[LABEL:.*]]
+; CHECK: br label %[[LABEL]]