[JumpThreading] A bug fix for stale loop info after unfold select

Summary:
The return value of a TryToUnfoldSelect call was not checked, which led to an
incorrectly preserved loop info and some crash.

The original crash was reported on https://reviews.llvm.org/D59514.

Reviewers: davidxl, amehsan

Reviewed By: davidxl

Subscribers: fhahn, brzycki, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D61920

llvm-svn: 360780
diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 123c8b9..7cb955d 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -1174,7 +1174,8 @@
   }
 
   if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator()))
-    TryToUnfoldSelect(SI, BB);
+    if (TryToUnfoldSelect(SI, BB))
+      return true;
 
   // Check for some cases that are worth simplifying.  Right now we want to look
   // for loads that are used by a switch or by the condition for the branch.  If
diff --git a/llvm/test/Transforms/JumpThreading/stale-loop-info-after-unfold-select.ll b/llvm/test/Transforms/JumpThreading/stale-loop-info-after-unfold-select.ll
new file mode 100644
index 0000000..7dbc794
--- /dev/null
+++ b/llvm/test/Transforms/JumpThreading/stale-loop-info-after-unfold-select.ll
@@ -0,0 +1,30 @@
+; RUN: opt -passes='require<loops>,jump-threading,verify<loops>' -S < %s
+
+%"type1" = type { i8 }
+%"type2" = type opaque
+
+define dso_local i16* @func2(%"type1"* %this, %"type2"*) {
+entry:
+  br label %while.cond
+
+while.cond:                                       ; preds = %func1.exit, %entry
+  %month.0 = phi i32 [ undef, %entry ], [ %month.0.be, %func1.exit ]
+  switch i32 %month.0, label %if.end.i [
+    i32 4, label %func1.exit
+    i32 1, label %func1.exit
+  ]
+
+if.end.i:                                         ; preds = %while.cond
+  br label %func1.exit
+
+func1.exit:                  ; preds = %if.end.i, %while.cond, %while.cond
+  %retval.0.i = phi i32 [ 9, %if.end.i ], [ 0, %while.cond ], [ 0, %while.cond ]
+  %call2 = tail call signext i32 @func3(i32 signext %retval.0.i, i32 signext 1, i32 signext 3)
+  %cmp = icmp slt i32 %call2, 1
+  %add = add nsw i32 %call2, 2
+  %month.0.be = select i1 %cmp, i32 %add, i32 %call2
+  br label %while.cond
+}
+
+declare i32 @func3(i32, i32, i32)
+