Rollup merge of #95202 - Urgau:check-cfg-perf-well-known-values, r=petrochenkov

Reduce the cost of loading all built-ins targets

This PR started by measuring the exact slowdown of checking of well known conditional values.
Than this PR implemented some technics to reduce the cost of loading all built-ins targets.

cf. https://github.com/rust-lang/rust/issues/82450#issuecomment-1073992323

5 files changed, 11 insertions, 9 deletions

diff --git a/compiler/rustc_codegen_llvm/src/attributes.rs b/compiler/rustc_codegen_llvm/src/attributes.rs
index 101da0012cb..c098ce36f02 100644
--- a/compiler/rustc_codegen_llvm/src/attributes.rs
+++ b/compiler/rustc_codegen_llvm/src/attributes.rs
@@ -116,7 +116,7 @@ fn instrument_function_attr<'ll>(cx: &CodegenCx<'ll, '_>) -> Option<&'ll Attribu
 
         // The function name varies on platforms.
         // See test/CodeGen/mcount.c in clang.
-        let mcount_name = cx.sess().target.mcount.as_str();
+        let mcount_name = cx.sess().target.mcount.as_ref();
 
         Some(llvm::CreateAttrStringValue(
             cx.llcx,
diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index c4eb593d297..1bbfc13e05e 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -1452,7 +1452,7 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
     }
 
     fn fptoint_sat_broken_in_llvm(&self) -> bool {
-        match self.tcx.sess.target.arch.as_str() {
+        match self.tcx.sess.target.arch.as_ref() {
             // FIXME - https://bugs.llvm.org/show_bug.cgi?id=50083
             "riscv64" => llvm_util::get_version() < (13, 0, 0),
             _ => false,
diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index 712431ca9ae..98cf873ebbd 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -134,7 +134,7 @@ pub unsafe fn create_module<'ll>(
     let mod_name = SmallCStr::new(mod_name);
     let llmod = llvm::LLVMModuleCreateWithNameInContext(mod_name.as_ptr(), llcx);
 
-    let mut target_data_layout = sess.target.data_layout.clone();
+    let mut target_data_layout = sess.target.data_layout.to_string();
     let llvm_version = llvm_util::get_version();
     if llvm_version < (13, 0, 0) {
         if sess.target.arch == "powerpc64" {
@@ -859,7 +859,7 @@ impl<'ll> CodegenCx<'ll, '_> {
 
         // This isn't an "LLVM intrinsic", but LLVM's optimization passes
         // recognize it like one and we assume it exists in `core::slice::cmp`
-        match self.sess().target.arch.as_str() {
+        match self.sess().target.arch.as_ref() {
             "avr" | "msp430" => ifn!("memcmp", fn(i8p, i8p, t_isize) -> t_i16),
             _ => ifn!("memcmp", fn(i8p, i8p, t_isize) -> t_i32),
         }
diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
index fe149b4c8c2..f4dc33452d1 100644
--- a/compiler/rustc_codegen_llvm/src/intrinsic.rs
+++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -329,7 +329,7 @@ impl<'ll, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'_, 'll, 'tcx> {
                     let b_ptr = self.bitcast(b, i8p_ty);
                     let n = self.const_usize(layout.size().bytes());
                     let cmp = self.call_intrinsic("memcmp", &[a_ptr, b_ptr, n]);
-                    match self.cx.sess().target.arch.as_str() {
+                    match self.cx.sess().target.arch.as_ref() {
                         "avr" | "msp430" => self.icmp(IntPredicate::IntEQ, cmp, self.const_i16(0)),
                         _ => self.icmp(IntPredicate::IntEQ, cmp, self.const_i32(0)),
                     }
diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
index abcdb81c0e2..c24e369ae72 100644
--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -61,8 +61,8 @@ unsafe fn configure_llvm(sess: &Session) {
         full_arg.trim().split(|c: char| c == '=' || c.is_whitespace()).next().unwrap_or("")
     }
 
-    let cg_opts = sess.opts.cg.llvm_args.iter();
-    let tg_opts = sess.target.llvm_args.iter();
+    let cg_opts = sess.opts.cg.llvm_args.iter().map(AsRef::as_ref);
+    let tg_opts = sess.target.llvm_args.iter().map(AsRef::as_ref);
     let sess_args = cg_opts.chain(tg_opts);
 
     let user_specified_args: FxHashSet<_> =
@@ -375,8 +375,10 @@ fn handle_native(name: &str) -> &str {
 }
 
 pub fn target_cpu(sess: &Session) -> &str {
-    let name = sess.opts.cg.target_cpu.as_ref().unwrap_or(&sess.target.cpu);
-    handle_native(name)
+    match sess.opts.cg.target_cpu {
+        Some(ref name) => handle_native(name),
+        None => handle_native(sess.target.cpu.as_ref()),
+    }
 }
 
 /// The list of LLVM features computed from CLI flags (`-Ctarget-cpu`, `-Ctarget-feature`,