From e0488c0961e5ba693d19f6e1e3f4c9b20631353b Mon Sep 17 00:00:00 2001
From: "Celina G. Val" <celinval@amazon.com>
Date: Wed, 13 Mar 2024 00:36:54 -0700
Subject: [PATCH] Fix StableMIR is_full computation

`WrappingRange::is_full` computation assumed that to be full the range
couldn't wrap, which is not necessarily true.

For example, a range of 1..=0 is a valid representation of a full
wrapping range.
---
 compiler/stable_mir/src/abi.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/stable_mir/src/abi.rs b/compiler/stable_mir/src/abi.rs
index 7fda9ceb79ac2..92bc2e34561ae 100644
--- a/compiler/stable_mir/src/abi.rs
+++ b/compiler/stable_mir/src/abi.rs
@@ -383,7 +383,7 @@ impl WrappingRange {
             return Err(error!("Expected size <= 128 bits, but found {} instead", size.bits()));
         };
         if self.start <= max_value && self.end <= max_value {
-            Ok(self.start == 0 && max_value == self.end)
+            Ok(self.start == (self.end.wrapping_add(1) & max_value))
         } else {
             Err(error!("Range `{self:?}` out of bounds for size `{}` bits.", size.bits()))
         }