Auto merge of #146697 - cjgillot:invalidate-patch, r=lcnr

Avoid invalidating CFG caches from MirPatch::apply.
Small effort to reduce invalidating CFG caches.

Author: bors

compiler/rustc_mir_transform/src/patch.rs

@@ -1,4 +1,5 @@
-use rustc_index::{Idx,IndexVec};
+use rustc_data_structures::fx::FxHashMap;
+use rustc_index::Idx;
 use rustc_middle::mir::*;
 use rustc_middle::ty::Ty;
 use rustc_span::Span;
@@ -9,7 +10,7 @@ use tracing::debug;
 /// and replacement of terminators, and then apply the queued changes all at
 /// once with `apply`. This is useful for MIR transformation passes.
 pub(crate)structMirPatch<'tcx>{
-term_patch_map:IndexVec<BasicBlock,Option<TerminatorKind<'tcx>>>,
+term_patch_map:FxHashMap<BasicBlock,TerminatorKind<'tcx>>,
 new_blocks:Vec<BasicBlockData<'tcx>>,
 new_statements:Vec<(Location,StatementKind<'tcx>)>,
 new_locals:Vec<LocalDecl<'tcx>>,
@@ -22,17 +23,21 @@ pub(crate) struct MirPatch<'tcx> {
 terminate_block:Option<(BasicBlock,UnwindTerminateReason)>,
 body_span:Span,
 next_local:usize,
+/// The number of blocks at the start of the transformation. New blocks
+/// get appended at the end.
+next_block:usize,
 }
 
 impl<'tcx>MirPatch<'tcx>{
 /// Creates a new, empty patch.
 pub(crate)fnnew(body:&Body<'tcx>) -> Self{
 letmut result = MirPatch{
-term_patch_map:IndexVec::from_elem(None,&body.basic_blocks),
+term_patch_map:Default::default(),
 new_blocks:vec![],
 new_statements:vec![],
 new_locals:vec![],
 next_local: body.local_decls.len(),
+next_block: body.basic_blocks.len(),
 resume_block:None,
 unreachable_cleanup_block:None,
 unreachable_no_cleanup_block:None,
@@ -141,7 +146,7 @@ impl<'tcx> MirPatch<'tcx> {
 
 /// Has a replacement of this block's terminator been queued in this patch?
 pub(crate)fnis_term_patched(&self,bb:BasicBlock) -> bool{
-self.term_patch_map[bb].is_some()
+self.term_patch_map.contains_key(&bb)
 }
 
 /// Universal getter for block data, either it is in 'old' blocks or in patched ones
@@ -194,18 +199,17 @@ impl<'tcx> MirPatch<'tcx> {
 
 /// Queues the addition of a new basic block.
 pub(crate)fnnew_block(&mutself,data:BasicBlockData<'tcx>) -> BasicBlock{
-let block = self.term_patch_map.next_index();
+let block = BasicBlock::from_usize(self.next_block + self.new_blocks.len());
 debug!("MirPatch: new_block: {:?}: {:?}", block, data);
 self.new_blocks.push(data);
-self.term_patch_map.push(None);
  block
 }
 
 /// Queues the replacement of a block's terminator.
 pub(crate)fnpatch_terminator(&mutself,block:BasicBlock,new:TerminatorKind<'tcx>){
-assert!(self.term_patch_map[block].is_none());
+assert!(!self.term_patch_map.contains_key(&block));
 debug!("MirPatch: patch_terminator({:?}, {:?})", block, new);
-self.term_patch_map[block] = Some(new);
+self.term_patch_map.insert(block,new);
 }
 
 /// Queues the insertion of a statement at a given location. The statement
@@ -244,18 +248,20 @@ impl<'tcx> MirPatch<'tcx> {
 self.new_blocks.len(),
  body.basic_blocks.len()
 );
+debug_assert_eq!(self.next_block, body.basic_blocks.len());
 let bbs = ifself.term_patch_map.is_empty() && self.new_blocks.is_empty(){
  body.basic_blocks.as_mut_preserves_cfg()
 }else{
  body.basic_blocks.as_mut()
 };
  bbs.extend(self.new_blocks);
  body.local_decls.extend(self.new_locals);
-for(src, patch)inself.term_patch_map.into_iter_enumerated(){
-ifletSome(patch) = patch {
-debug!("MirPatch: patching block {:?}", src);
- bbs[src].terminator_mut().kind = patch;
-}
+
+// The order in which we patch terminators does not change the result.
+#[allow(rustc::potential_query_instability)]
+for(src, patch)inself.term_patch_map{
+debug!("MirPatch: patching block {:?}", src);
+ bbs[src].terminator_mut().kind = patch;
 }
 
 letmut new_statements = self.new_statements;
@@ -273,8 +279,8 @@ impl<'tcx> MirPatch<'tcx> {
 }
 debug!("MirPatch: adding statement {:?} at loc {:?}+{}", stmt, loc, delta);
  loc.statement_index += delta;
-let source_info = Self::source_info_for_index(&body[loc.block], loc);
-body[loc.block]
+let source_info = Self::source_info_for_index(&bbs[loc.block], loc);
+bbs[loc.block]
 .statements
 .insert(loc.statement_index,Statement::new(source_info, stmt));
  delta += 1;