Change RangeInclusive to a three-field struct.

Fix #45222.

src/test/codegen/issue-45222.rs

@@ -0,0 +1,74 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -O
+// min-llvm-version 6.0
+
+#![crate_type = "lib"]
+
+// verify that LLVM recognizes a loop involving 0..=n and will const-fold it.
+
+//------------------------------------------------------------------------------
+// Example from original issue #45222
+
+fn foo2(n: u64) -> u64 {
+    let mut count = 0;
+    for _ in 0..n {
+        for j in (0..=n).rev() {
+            count += j;
+        }
+    }
+    count
+}
+
+// CHECK-LABEL: @check_foo2
+#[no_mangle]
+pub fn check_foo2() -> u64 {
+    // CHECK: ret i64 500005000000000
+    foo2(100000)
+}
+
+//------------------------------------------------------------------------------
+// Simplified example of #45222
+
+fn triangle_inc(n: u64) -> u64 {
+    let mut count = 0;
+    for j in 0 ..= n {
+        count += j;
+    }
+    count
+}
+
+// CHECK-LABEL: @check_triangle_inc
+#[no_mangle]
+pub fn check_triangle_inc() -> u64 {
+    // CHECK: ret i64 5000050000
+    triangle_inc(100000)
+}
+
+//------------------------------------------------------------------------------
+// Demo in #48012
+
+fn foo3r(n: u64) -> u64 {
+    let mut count = 0;
+    (0..n).for_each(|_| {
+        (0 ..= n).rev().for_each(|j| {
+            count += j;
+        })
+    });
+    count
+}
+
+// CHECK-LABEL: @check_foo3r
+#[no_mangle]
+pub fn check_foo3r() -> u64 {
+    // CHECK: ret i64 500005000000000
+    foo3r(100000)
+}