[InstCombine] Add test for infinite combine loop (NFC)

Test courtesy of bkramer for the infinite combine loop introduced
by D87480.

diff --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index d9a4f4b..6c3e577 100644 (file)
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -2683,5 +2683,20 @@ define i8 @select_replacement_loop(i8 %x, i8 %y, i8 %z) {
   ret i8 %sel
 }
 
+define i32 @select_replacement_loop2(i32 %arg, i32 %arg2) {
+; CHECK-LABEL: @select_replacement_loop2(
+; CHECK-NEXT:    [[DIV:%.*]] = udiv i32 [[ARG:%.*]], [[ARG2:%.*]]
+; CHECK-NEXT:    [[MUL:%.*]] = mul nsw i32 [[DIV]], [[ARG2]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[MUL]], [[ARG]]
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i32 [[DIV]], i32 undef
+; CHECK-NEXT:    ret i32 [[SEL]]
+;
+  %div = udiv i32 %arg, %arg2
+  %mul = mul nsw i32 %div, %arg2
+  %cmp = icmp eq i32 %mul, %arg
+  %sel = select i1 %cmp, i32 %div, i32 undef
+  ret i32 %sel
+}
+
 declare void @use(i1)
 declare i32 @llvm.cttz.i32(i32, i1 immarg)