[JumpThreading] Add test for #70651 (NFC)

Author: nikic

llvm/test/Transforms/JumpThreading/pr70651.ll

@@ -0,0 +1,32 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
+; RUN: opt -S -passes=jump-threading < %s | FileCheck %s
+
+; FIXME: This is a miscompile.
+define i64 @test(i64 %v) {
+; CHECK-LABEL: define i64 @test(
+; CHECK-SAME: i64 [[V:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[V_NONNEG:%.*]] = icmp sgt i64 [[V]], -1
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[SUM:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[SUM_NEXT]] = add i64 [[SUM]], [[V]]
+; CHECK-NEXT:    [[OVERFLOW:%.*]] = icmp ult i64 [[SUM_NEXT]], [[SUM]]
+; CHECK-NEXT:    br i1 [[V_NONNEG]], label [[FOR_BODY]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i64 [[SUM]]
+;
+entry:
+  %v.nonneg = icmp sgt i64 %v, -1
+  br label %for.body
+
+for.body:
+  %sum = phi i64 [ 0, %entry ], [ %sum.next, %for.body ]
+  %sum.next = add i64 %sum, %v
+  %overflow = icmp ult i64 %sum.next, %sum
+  %cmp = xor i1 %v.nonneg, %overflow
+  br i1 %cmp, label %for.body, label %exit
+
+exit:
+  ret i64 %sum
+}