Fix StableMIR is_full computation

celinval · celinval · commit e0488c0961e5 · 2024-03-13T00:36:54.000-07:00
`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.
diff --git 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()))
         }

Original file line number	Diff line number	Diff line change
`@@ -383,7 +383,7 @@ impl WrappingRange {`
`383`	`383`	`return Err(error!("Expected size <= 128 bits, but found {} instead", size.bits()));`
`384`	`384`	`};`
`385`	`385`	`if self.start <= max_value && self.end <= max_value {`
`386`		`- Ok(self.start == 0 && max_value == self.end)`
	`386`	`+ Ok(self.start == (self.end.wrapping_add(1) & max_value))`
`387`	`387`	`} else {`
`388`	`388`	Err(error!("Range `{self:?}` out of bounds for size `{}` bits.", size.bits()))
`389`	`389`	`}`