CorrelatedPropagation: BasicBlock::removePredecessor can simplify PHI nodes. If the it's the condition of a SwitchInst, reload it.

Fixes PR13972.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164818 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/CorrelatedValuePropagation.cpp

@@ -235,6 +235,11 @@ bool CorrelatedValuePropagation::processSwitch(SwitchInst *SI) {
       // This case never fires - remove it.
       CI.getCaseSuccessor()->removePredecessor(BB);
       SI->removeCase(CI); // Does not invalidate the iterator.
+
+      // The condition can be modified by removePredecessor's PHI simplification
+      // logic.
+      Cond = SI->getCondition();
+
       ++NumDeadCases;
       Changed = true;
     } else if (State == LazyValueInfo::True) {

test/Transforms/CorrelatedValuePropagation/crash.ll

@@ -35,3 +35,28 @@ srf.exit.i:
 func_29.exit:
   ret void
 }
+
+; PR13972
+define void @test3() nounwind {
+for.body:
+  br label %return
+
+for.cond.i:                                       ; preds = %if.else.i, %for.body.i
+  %e.2.i = phi i32 [ %e.2.i, %if.else.i ], [ -8, %for.body.i ]
+  br i1 undef, label %return, label %for.body.i
+
+for.body.i:                                       ; preds = %for.cond.i
+  switch i32 %e.2.i, label %for.cond3.i [
+    i32 -3, label %if.else.i
+    i32 0, label %for.cond.i
+  ]
+
+for.cond3.i:                                      ; preds = %for.cond3.i, %for.body.i
+  br label %for.cond3.i
+
+if.else.i:                                        ; preds = %for.body.i
+  br label %for.cond.i
+
+return:                                           ; preds = %for.cond.i, %for.body
+  ret void
+}