[PATCH] reset iterators when more than one dead code instruction is removed

[Gerolf Hoflehner]

Hi

a few places invoke dead instruction removal, but assume only one instruction gets removed. This patch 
resets the iterators when dead instructions have been removed.

Gerolf


Index: lib/Transforms/Scalar/LoopInstSimplify.cpp
===================================================================
--- lib/Transforms/Scalar/LoopInstSimplify.cpp  (revision 206487)
+++ lib/Transforms/Scalar/LoopInstSimplify.cpp  (working copy)
@@ -126,7 +126,15 @@
             ++NumSimplified;
           }
         }
-        LocalChanged |= 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();
+          LocalChanged |= res;
+        }
 
         if (IsSubloopHeader && !isa<PHINode>(I))
           break;
Index: lib/Transforms/Utils/SimplifyInstructions.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyInstructions.cpp       (revision 206487)
+++ lib/Transforms/Utils/SimplifyInstructions.cpp       (working copy)
@@ -75,7 +75,15 @@
                 ++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
Index: test/Transforms/InstSimplify/dead-code-removal.ll
===================================================================
--- test/Transforms/InstSimplify/dead-code-removal.ll   (revision 0)
+++ test/Transforms/InstSimplify/dead-code-removal.ll   (working copy)
@@ -0,0 +1,15 @@
+; RUN: opts -instsimplify -S < %s | FileCheck %s
+
+define void @foo() nounwind {
+  br i1 undef, label %1, label %4
+
+; <label>:1                                       ; preds = %1, %0
+; CHECK-NOT: phi
+; CHECK-NOT: sub
+  %2 = phi i32 [ %3, %1 ], [ undef, %0 ]
+  %3 = sub i32 0, undef
+  br label %1
+
+; <label>:4                                       ; preds = %0
+  ret void
+}

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