Auto merge of #123185 - scottmcm:more-typed-copy, r=compiler-errors

Remove my `scalar_copy_backend_type` optimization attempt

I added this back in https://github.com/rust-lang/rust/pull/111999 , but I no longer think it's a good idea
- It had to get scaled back to only power-of-two things to not break a bunch of targets
- LLVM seems to be getting better at memcpy removal anyway
- Introducing vector instructions has seemed to sometimes (https://github.com/rust-lang/rust/pull/115515#issuecomment-1750069529) make autovectorization worse

So this removes it from the codegen crates entirely, and instead just tries to use <https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/traits/builder/trait.BuilderMethods.html#method.typed_place_copy> instead of direct `memcpy` so things will still use load/store when a type isn't `OperandValue::Ref`.

1 files changed, 3 insertions, 35 deletions

diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index c4c16ee7311..930b9b8c0db 100644
--- a/compiler/rustc_codegen_ssa/src/base.rs
+++ b/compiler/rustc_codegen_ssa/src/base.rs
@@ -12,7 +12,7 @@ use crate::mir;
 use crate::mir::operand::OperandValue;
 use crate::mir::place::PlaceRef;
 use crate::traits::*;
-use crate::{CachedModuleCodegen, CompiledModule, CrateInfo, MemFlags, ModuleCodegen, ModuleKind};
+use crate::{CachedModuleCodegen, CompiledModule, CrateInfo, ModuleCodegen, ModuleKind};
 
 use rustc_ast::expand::allocator::{global_fn_name, AllocatorKind, ALLOCATOR_METHODS};
 use rustc_attr as attr;
@@ -37,7 +37,7 @@ use rustc_session::config::{self, CrateType, EntryFnType, OptLevel, OutputType};
 use rustc_session::Session;
 use rustc_span::symbol::sym;
 use rustc_span::Symbol;
-use rustc_target::abi::{Align, FIRST_VARIANT};
+use rustc_target::abi::FIRST_VARIANT;
 
 use std::cmp;
 use std::collections::BTreeSet;
@@ -282,15 +282,7 @@ pub fn coerce_unsized_into<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
                 }
 
                 if src_f.layout.ty == dst_f.layout.ty {
-                    memcpy_ty(
-                        bx,
-                        dst_f.llval,
-                        dst_f.align,
-                        src_f.llval,
-                        src_f.align,
-                        src_f.layout,
-                        MemFlags::empty(),
-                    );
+                    bx.typed_place_copy(dst_f, src_f);
                 } else {
                     coerce_unsized_into(bx, src_f, dst_f);
                 }
@@ -382,30 +374,6 @@ pub fn wants_new_eh_instructions(sess: &Session) -> bool {
     wants_wasm_eh(sess) || wants_msvc_seh(sess)
 }
 
-pub fn memcpy_ty<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
-    bx: &mut Bx,
-    dst: Bx::Value,
-    dst_align: Align,
-    src: Bx::Value,
-    src_align: Align,
-    layout: TyAndLayout<'tcx>,
-    flags: MemFlags,
-) {
-    let size = layout.size.bytes();
-    if size == 0 {
-        return;
-    }
-
-    if flags == MemFlags::empty()
-        && let Some(bty) = bx.cx().scalar_copy_backend_type(layout)
-    {
-        let temp = bx.load(bty, src, src_align);
-        bx.store(temp, dst, dst_align);
-    } else {
-        bx.memcpy(dst, dst_align, src, src_align, bx.cx().const_usize(size), flags);
-    }
-}
-
 pub fn codegen_instance<'a, 'tcx: 'a, Bx: BuilderMethods<'a, 'tcx>>(
     cx: &'a Bx::CodegenCx,
     instance: Instance<'tcx>,