Auto merge of rust-lang#122567 - erikdesjardins:noname, r=<try>

Avoid naming LLVM basic blocks when `fewer_names` is true

This may be a small perf win.

r? `@ghost`

compiler/rustc_codegen_llvm/src/builder.rs

@@ -155,8 +155,14 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
 
     fn append_block(cx: &'a CodegenCx<'ll, 'tcx>, llfn: &'ll Value, name: &str) -> &'ll BasicBlock {
         unsafe {
-            let name = SmallCStr::new(name);
-            llvm::LLVMAppendBasicBlockInContext(cx.llcx, llfn, name.as_ptr())
+            let c_str_name;
+            let name_ptr = if cx.tcx.sess.fewer_names() {
+                const { c"".as_ptr().cast() }
+            } else {
+                c_str_name = SmallCStr::new(name);
+                c_str_name.as_ptr()
+            };
+            llvm::LLVMAppendBasicBlockInContext(cx.llcx, llfn, name_ptr)
         }
     }
 

compiler/rustc_codegen_llvm/src/lib.rs

@@ -11,6 +11,7 @@
 #![feature(exact_size_is_empty)]
 #![feature(extern_types)]
 #![feature(hash_raw_entry)]
+#![feature(inline_const)]
 #![feature(iter_intersperse)]
 #![feature(let_chains)]
 #![feature(impl_trait_in_assoc_type)]

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -1688,7 +1688,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
     pub fn try_llbb(&mut self, bb: mir::BasicBlock) -> Option<Bx::BasicBlock> {
         match self.cached_llbbs[bb] {
             CachedLlbb::None => {
-                // FIXME(eddyb) only name the block if `fewer_names` is `false`.
                 let llbb = Bx::append_block(self.cx, self.llfn, &format!("{bb:?}"));
                 self.cached_llbbs[bb] = CachedLlbb::Some(llbb);
                 Some(llbb)