Auto merge of #113116 - nnethercote:codegen-opts, r=oli-obk

A mish-mash of micro-optimizations

These were aimed at speeding up LLVM codegen, but ended up affecting other places as well.

r? `@bjorn3`

3 files changed, 6 insertions, 6 deletions

diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/create_scope_map.rs b/compiler/rustc_codegen_llvm/src/debuginfo/create_scope_map.rs
index 64961baf272..65cbd5edc59 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/create_scope_map.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/create_scope_map.rs
@@ -65,10 +65,10 @@ fn make_mir_scope<'ll, 'tcx>(
         debug_context.scopes[parent]
     } else {
         // The root is the function itself.
-        let loc = cx.lookup_debug_loc(mir.span.lo());
+        let file = cx.sess().source_map().lookup_source_file(mir.span.lo());
         debug_context.scopes[scope] = DebugScope {
-            file_start_pos: loc.file.start_pos,
-            file_end_pos: loc.file.end_pos,
+            file_start_pos: file.start_pos,
+            file_end_pos: file.end_pos,
             ..debug_context.scopes[scope]
         };
         instantiated.insert(scope);
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs b/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs
index aa7ae9355bc..c2f16cad3fc 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs
@@ -262,7 +262,7 @@ impl CodegenCx<'_, '_> {
     pub fn lookup_debug_loc(&self, pos: BytePos) -> DebugLoc {
         let (file, line, col) = match self.sess().source_map().lookup_line(pos) {
             Ok(SourceFileAndLine { sf: file, line }) => {
-                let line_pos = file.line_begin_pos(pos);
+                let line_pos = file.lines(|lines| lines[line]);
 
                 // Use 1-based indexing.
                 let line = (line + 1) as u32;
@@ -331,7 +331,7 @@ impl<'ll, 'tcx> DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
             llvm::LLVMRustDIBuilderCreateSubroutineType(DIB(self), fn_signature)
         };
 
-        let mut name = String::new();
+        let mut name = String::with_capacity(64);
         type_names::push_item_name(tcx, def_id, false, &mut name);
 
         // Find the enclosing function, in case this is a closure.
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/namespace.rs b/compiler/rustc_codegen_llvm/src/debuginfo/namespace.rs
index d5ea48c311b..fa61c7dde18 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/namespace.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/namespace.rs
@@ -28,7 +28,7 @@ pub fn item_namespace<'ll>(cx: &CodegenCx<'ll, '_>, def_id: DefId) -> &'ll DISco
         .map(|parent| item_namespace(cx, DefId { krate: def_id.krate, index: parent }));
 
     let namespace_name_string = {
-        let mut output = String::new();
+        let mut output = String::with_capacity(64);
         type_names::push_item_name(cx.tcx, def_id, false, &mut output);
         output
     };