Rollup merge of #110402 - scottmcm:align-tz, r=fee1-dead

fee1-dead · web-flow · commit 38215fb77aca · 2023-04-16T19:36:03.000+08:00
Remove the loop in `Align::from_bytes`

Perf is almost certainly irrelevant, but might as well simplify it, since `trailing_zeros` does exactly what's needed.
diff --git a/compiler/rustc_abi/src/lib.rs b/compiler/rustc_abi/src/lib.rs
@@ -665,15 +665,12 @@ impl Align {
             format!("`{}` is too large", align)
         }
 
-        let mut bytes = align;
-        let mut pow2: u8 = 0;
-        while (bytes & 1) == 0 {
-            pow2 += 1;
-            bytes >>= 1;
-        }
-        if bytes != 1 {
+        let tz = align.trailing_zeros();
+        if align != (1 << tz) {
             return Err(not_power_of_2(align));
         }
+
+        let pow2 = tz as u8;
         if pow2 > Self::MAX.pow2 {
             return Err(too_large(align));
         }

Original file line number	Diff line number	Diff line change
`@@ -665,15 +665,12 @@ impl Align {`
`665`	`665`	format!("`{}` is too large", align)
`666`	`666`	`}`
`667`	`667`
`668`		`- let mut bytes = align;`
`669`		`- let mut pow2: u8 = 0;`
`670`		`- while (bytes & 1) == 0 {`
`671`		`- pow2 += 1;`
`672`		`- bytes >>= 1;`
`673`		`- }`
`674`		`- if bytes != 1 {`
	`668`	`+ let tz = align.trailing_zeros();`
	`669`	`+ if align != (1 << tz) {`
`675`	`670`	`return Err(not_power_of_2(align));`
`676`	`671`	`}`
	`672`	`+`
	`673`	`+ let pow2 = tz as u8;`
`677`	`674`	`if pow2 > Self::MAX.pow2 {`
`678`	`675`	`return Err(too_large(align));`
`679`	`676`	`}`