Auto merge of #96281 - SparrowLii:const_prop, r=wesleywiser

Optimize `const_prop` mir-opt by accessing `local_decls` through `ecx`

From the FIXME in the impl of `ConstPropagator`. Accessing `local_decls` and `scource_scopes` from `ecx` can reduce `clone` calls and save compile time.
Besides, according to #96213 , the FIXME about writing `layouts` to `ecx` in advance can also be removed.

Author: bors

compiler/rustc_mir_transform/src/const_prop.rs

@@ -313,9 +313,7 @@ struct ConstPropagator<'mir, 'tcx> {
     ecx: InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>,
     tcx: TyCtxt<'tcx>,
     param_env: ParamEnv<'tcx>,
-    // FIXME(eddyb) avoid cloning this field more than once,
-    // by accessing it through `ecx` instead.
-    local_decls: IndexVec<Local, LocalDecl<'tcx>>,
+    local_decls: &'mir IndexVec<Local, LocalDecl<'tcx>>,
     // Because we have `MutVisitor` we can't obtain the `SourceInfo` from a `Location`. So we store
     // the last known `SourceInfo` here and just keep revisiting it.
     source_info: Option<SourceInfo>,
@@ -361,10 +359,6 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
         let substs = &InternalSubsts::identity_for_item(tcx, def_id);
         let param_env = tcx.param_env_reveal_all_normalized(def_id);
 
-        let span = tcx.def_span(def_id);
-        // FIXME: `CanConstProp::check` computes the layout of all locals, return those layouts
-        // so we can write them to `ecx.frame_mut().locals.layout, reducing the duplication in
-        // `layout_of` query invocations.
         let can_const_prop = CanConstProp::check(tcx, param_env, body);
         let mut only_propagate_inside_block_locals = BitSet::new_empty(can_const_prop.len());
         for (l, mode) in can_const_prop.iter_enumerated() {
@@ -374,7 +368,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
         }
         let mut ecx = InterpCx::new(
             tcx,
-            span,
+            tcx.def_span(def_id),
             param_env,
             ConstPropMachine::new(only_propagate_inside_block_locals, can_const_prop),
         );
@@ -405,10 +399,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             ecx,
             tcx,
             param_env,
-            // FIXME(eddyb) avoid cloning this field more than once,
-            // by accessing it through `ecx` instead.
-            //FIXME(wesleywiser) we can't steal this because `Visitor::super_visit_body()` needs it
-            local_decls: body.local_decls.clone(),
+            local_decls: &dummy_body.local_decls,
             source_info: None,
         }
     }
@@ -511,7 +502,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             let r = r?;
             // We need the type of the LHS. We cannot use `place_layout` as that is the type
             // of the result, which for checked binops is not the same!
-            let left_ty = left.ty(&self.local_decls, self.tcx);
+            let left_ty = left.ty(self.local_decls, self.tcx);
             let left_size = self.ecx.layout_of(left_ty).ok()?.size;
             let right_size = r.layout.size;
             let r_bits = r.to_scalar().ok();

compiler/rustc_mir_transform/src/const_prop_lint.rs

@@ -308,10 +308,8 @@ struct ConstPropagator<'mir, 'tcx> {
     ecx: InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>,
     tcx: TyCtxt<'tcx>,
     param_env: ParamEnv<'tcx>,
-    // FIXME(eddyb) avoid cloning these two fields more than once,
-    // by accessing them through `ecx` instead.
-    source_scopes: IndexVec<SourceScope, SourceScopeData<'tcx>>,
-    local_decls: IndexVec<Local, LocalDecl<'tcx>>,
+    source_scopes: &'mir IndexVec<SourceScope, SourceScopeData<'tcx>>,
+    local_decls: &'mir IndexVec<Local, LocalDecl<'tcx>>,
     // Because we have `MutVisitor` we can't obtain the `SourceInfo` from a `Location`. So we store
     // the last known `SourceInfo` here and just keep revisiting it.
     source_info: Option<SourceInfo>,
@@ -357,10 +355,6 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
         let substs = &InternalSubsts::identity_for_item(tcx, def_id);
         let param_env = tcx.param_env_reveal_all_normalized(def_id);
 
-        let span = tcx.def_span(def_id);
-        // FIXME: `CanConstProp::check` computes the layout of all locals, return those layouts
-        // so we can write them to `ecx.frame_mut().locals.layout, reducing the duplication in
-        // `layout_of` query invocations.
         let can_const_prop = CanConstProp::check(tcx, param_env, body);
         let mut only_propagate_inside_block_locals = BitSet::new_empty(can_const_prop.len());
         for (l, mode) in can_const_prop.iter_enumerated() {
@@ -370,7 +364,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
         }
         let mut ecx = InterpCx::new(
             tcx,
-            span,
+            tcx.def_span(def_id),
             param_env,
             ConstPropMachine::new(only_propagate_inside_block_locals, can_const_prop),
         );
@@ -401,11 +395,8 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             ecx,
             tcx,
             param_env,
-            // FIXME(eddyb) avoid cloning these two fields more than once,
-            // by accessing them through `ecx` instead.
-            source_scopes: body.source_scopes.clone(),
-            //FIXME(wesleywiser) we can't steal this because `Visitor::super_visit_body()` needs it
-            local_decls: body.local_decls.clone(),
+            source_scopes: &dummy_body.source_scopes,
+            local_decls: &dummy_body.local_decls,
             source_info: None,
         }
     }
@@ -435,7 +426,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
     }
 
     fn lint_root(&self, source_info: SourceInfo) -> Option<HirId> {
-        source_info.scope.lint_root(&self.source_scopes)
+        source_info.scope.lint_root(self.source_scopes)
     }
 
     fn use_ecx<F, T>(&mut self, f: F) -> Option<T>
@@ -572,7 +563,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             let r = r?;
             // We need the type of the LHS. We cannot use `place_layout` as that is the type
             // of the result, which for checked binops is not the same!
-            let left_ty = left.ty(&self.local_decls, self.tcx);
+            let left_ty = left.ty(self.local_decls, self.tcx);
             let left_size = self.ecx.layout_of(left_ty).ok()?.size;
             let right_size = r.layout.size;
             let r_bits = r.to_scalar().ok();