Fix PR3353, infinitely jump threading an infinite loop make from switches.

llvm-svn: 62529

llvm/lib/Transforms/Scalar/JumpThreading.cpp

@@ -419,6 +419,11 @@ bool JumpThreading::ProcessBranchOnDuplicateCond(BasicBlock *PredBB,
 /// switches out of repeated 'if' conditions.
 bool JumpThreading::ProcessSwitchOnDuplicateCond(BasicBlock *PredBB,
                                                  BasicBlock *DestBB) {
+  // Can't thread edge to self.
+  if (PredBB == DestBB)
+    return false;
+  
+  
   SwitchInst *PredSI = cast<SwitchInst>(PredBB->getTerminator());
   SwitchInst *DestSI = cast<SwitchInst>(DestBB->getTerminator());
 

llvm/test/Transforms/JumpThreading/2009-01-19-InfSwitchLoop.ll

+; RUN: llvm-as < %s | opt -jump-threading | llvm-dis
+; PR3353
+
+define i32 @test(i8 %X) {
+entry:
+	%Y = add i8 %X, 1
+	%Z = add i8 %Y, 1
+	br label %bb33.i
+
+bb33.i:		; preds = %bb33.i, %bb32.i
+	switch i8 %Y, label %bb32.i [
+		i8 39, label %bb35.split.i
+		i8 13, label %bb33.i
+	]
+
+bb35.split.i:
+	ret i32 5
+bb32.i:
+	ret i32 1
+}
+