Auto merge of #102570 - cjgillot:deagg-debuginfo, r=oli-obk

Perform simple scalar replacement of aggregates (SROA) MIR opt

This is a re-open of https://github.com/rust-lang/rust/pull/85796

I copied the debuginfo implementation (first commit) from `@eddyb's` own SROA PR.

This pass replaces plain field accesses by simple locals when possible.
To be eligible, the replaced locals:
- must not be enums or unions;
- must not be used whole;
- must not have their address taken.

The storage and deinit statements are duplicated on each created local.

cc `@tmiasko` who reviewed the former version of this PR.

src/debuginfo.rs

@@ -4,8 +4,9 @@ use rustc_codegen_ssa::traits::{DebugInfoBuilderMethods, DebugInfoMethods};
 use rustc_middle::mir;
 use rustc_middle::ty::{Instance, PolyExistentialTraitRef, Ty};
 use rustc_span::{SourceFile, Span, Symbol};
-use rustc_target::abi::Size;
 use rustc_target::abi::call::FnAbi;
+use rustc_target::abi::Size;
+use std::ops::Range;
 
 use crate::builder::Builder;
 use crate::context::CodegenCx;
@@ -13,7 +14,15 @@ use crate::context::CodegenCx;
 impl<'a, 'gcc, 'tcx> DebugInfoBuilderMethods for Builder<'a, 'gcc, 'tcx> {
     // FIXME(eddyb) find a common convention for all of the debuginfo-related
     // names (choose between `dbg`, `debug`, `debuginfo`, `debug_info` etc.).
-    fn dbg_var_addr(&mut self, _dbg_var: Self::DIVariable, _scope_metadata: Self::DIScope, _variable_alloca: Self::Value, _direct_offset: Size, _indirect_offsets: &[Size]) {
+    fn dbg_var_addr(
+        &mut self,
+        _dbg_var: Self::DIVariable,
+        _scope_metadata: Self::DIScope,
+        _variable_alloca: Self::Value,
+        _direct_offset: Size,
+        _indirect_offsets: &[Size],
+        _fragment: Option<Range<Size>>,
+    ) {
         unimplemented!();
     }
 
@@ -31,16 +40,31 @@ impl<'a, 'gcc, 'tcx> DebugInfoBuilderMethods for Builder<'a, 'gcc, 'tcx> {
 }
 
 impl<'gcc, 'tcx> DebugInfoMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
-    fn create_vtable_debuginfo(&self, _ty: Ty<'tcx>, _trait_ref: Option<PolyExistentialTraitRef<'tcx>>, _vtable: Self::Value) {
+    fn create_vtable_debuginfo(
+        &self,
+        _ty: Ty<'tcx>,
+        _trait_ref: Option<PolyExistentialTraitRef<'tcx>>,
+        _vtable: Self::Value,
+    ) {
         // TODO(antoyo)
     }
 
-    fn create_function_debug_context(&self, _instance: Instance<'tcx>, _fn_abi: &FnAbi<'tcx, Ty<'tcx>>, _llfn: RValue<'gcc>, _mir: &mir::Body<'tcx>) -> Option<FunctionDebugContext<Self::DIScope, Self::DILocation>> {
+    fn create_function_debug_context(
+        &self,
+        _instance: Instance<'tcx>,
+        _fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
+        _llfn: RValue<'gcc>,
+        _mir: &mir::Body<'tcx>,
+    ) -> Option<FunctionDebugContext<Self::DIScope, Self::DILocation>> {
         // TODO(antoyo)
         None
     }
 
-    fn extend_scope_to_file(&self, _scope_metadata: Self::DIScope, _file: &SourceFile) -> Self::DIScope {
+    fn extend_scope_to_file(
+        &self,
+        _scope_metadata: Self::DIScope,
+        _file: &SourceFile,
+    ) -> Self::DIScope {
         unimplemented!();
     }
 
@@ -48,15 +72,32 @@ impl<'gcc, 'tcx> DebugInfoMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
         // TODO(antoyo)
     }
 
-    fn create_dbg_var(&self, _variable_name: Symbol, _variable_type: Ty<'tcx>, _scope_metadata: Self::DIScope, _variable_kind: VariableKind, _span: Span) -> Self::DIVariable {
+    fn create_dbg_var(
+        &self,
+        _variable_name: Symbol,
+        _variable_type: Ty<'tcx>,
+        _scope_metadata: Self::DIScope,
+        _variable_kind: VariableKind,
+        _span: Span,
+    ) -> Self::DIVariable {
         unimplemented!();
     }
 
-    fn dbg_scope_fn(&self, _instance: Instance<'tcx>, _fn_abi: &FnAbi<'tcx, Ty<'tcx>>, _maybe_definition_llfn: Option<RValue<'gcc>>) -> Self::DIScope {
+    fn dbg_scope_fn(
+        &self,
+        _instance: Instance<'tcx>,
+        _fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
+        _maybe_definition_llfn: Option<RValue<'gcc>>,
+    ) -> Self::DIScope {
         unimplemented!();
     }
 
-    fn dbg_loc(&self, _scope: Self::DIScope, _inlined_at: Option<Self::DILocation>, _span: Span) -> Self::DILocation {
+    fn dbg_loc(
+        &self,
+        _scope: Self::DIScope,
+        _inlined_at: Option<Self::DILocation>,
+        _span: Span,
+    ) -> Self::DILocation {
         unimplemented!();
     }
 }