Auto merge of rust-lang#129771 - bvanjoi:donot-clone-old-syntax-context, r=<try>

bors · bors · commit 89b15693dc0b · 2024-08-30T02:03:33.000Z
dont clone old syntax context I guess this regression was caused by too many clones, so this is an attempt to use the old value rather than cloning it. Perhaps a better approach would be to ensure that only the substantial fields mentioned in this [comment](rust-lang#127279 (comment)) are cacheable. Anyway, let's run a perf test to see if this can solve the problem. r? `@pnkfelix` or `@petrochenkov`
diff --git a/compiler/rustc_span/src/hygiene.rs b/compiler/rustc_span/src/hygiene.rs
@@ -1420,7 +1420,8 @@ pub fn decode_syntax_context<D: Decoder, F: FnOnce(&mut D, u32) -> SyntaxContext
             && old.outer_transparency == ctxt_data.outer_transparency
             && old.parent == ctxt_data.parent
         {
-            ctxt_data = old.clone();
+            ctxt_data.opaque = old.opaque;
+            ctxt_data.opaque_and_semitransparent = old.opaque_and_semitransparent;
         }
 
         let dummy = std::mem::replace(

Original file line number	Diff line number	Diff line change
`@@ -1420,7 +1420,8 @@ pub fn decode_syntax_context<D: Decoder, F: FnOnce(&mut D, u32) -> SyntaxContext`
`1420`	`1420`	`&& old.outer_transparency == ctxt_data.outer_transparency`
`1421`	`1421`	`&& old.parent == ctxt_data.parent`
`1422`	`1422`	`{`
`1423`		`- ctxt_data = old.clone();`
	`1423`	`+ ctxt_data.opaque = old.opaque;`
	`1424`	`+ ctxt_data.opaque_and_semitransparent = old.opaque_and_semitransparent;`
`1424`	`1425`	`}`
`1425`	`1426`
`1426`	`1427`	`let dummy = std::mem::replace(`