fix PR9013, an infinite loop in instcombine.

llvm-svn: 123968

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -538,9 +538,11 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I) {
   if (!PN->hasOneUse()) {
     // Walk the use list for the instruction, comparing them to I.
     for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end();
-         UI != E; ++UI)
-      if (!I.isIdenticalTo(cast<Instruction>(*UI))) 
+         UI != E; ++UI) {
+      Instruction *User = cast<Instruction>(*UI);
+      if (User != &I && !I.isIdenticalTo(User))
         return 0;
+    }
     // Otherwise, we can replace *all* users with the new PHI we form.
   }
   
@@ -565,6 +567,12 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I) {
     if (InvokeInst *II = dyn_cast<InvokeInst>(InVal))
       if (II->getParent() == NonConstBB)
         return 0;
+    
+    // If the incoming non-constant value is in I's block, we will remove one
+    // instruction, but insert another equivalent one, leading to infinite
+    // instcombine.
+    if (NonConstBB == I.getParent())
+      return 0;
   }
   
   // If there is exactly one non-constant value, we can insert a copy of the

llvm/test/Transforms/InstCombine/crash.ll

@@ -353,3 +353,20 @@ entry:
   ret %struct.basic_ios* %0
 }
 
+; PR9013
+define void @test18() nounwind ssp {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc, %entry
+  %l_197.0 = phi i32 [ 0, %entry ], [ %sub.i, %for.inc ]
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.cond
+  %conv = and i32 %l_197.0, 255
+  %sub.i = add nsw i32 %conv, -1
+  br label %for.cond
+
+return:                                           ; No predecessors!
+  ret void
+}