Auto merge of #111673 - cjgillot:dominator-preprocess, r=cjgillot,tmiasko

Preprocess and cache dominator tree

Preprocessing dominators has a very strong effect for https://github.com/rust-lang/rust/pull/111344.
That pass checks that assignments dominate their uses repeatedly. Using the unprocessed dominator tree caused a quadratic runtime (number of bbs x depth of the dominator tree).

This PR also caches the dominator tree and the pre-processed dominators in the MIR cfg cache.

Rebase of https://github.com/rust-lang/rust/pull/107157
cc `@tmiasko`

compiler/rustc_codegen_ssa/src/mir/analyze.rs

@@ -84,7 +84,7 @@ impl DefLocation {
 
 struct LocalAnalyzer<'mir, 'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> {
     fx: &'mir FunctionCx<'a, 'tcx, Bx>,
-    dominators: Dominators<mir::BasicBlock>,
+    dominators: &'mir Dominators<mir::BasicBlock>,
     locals: IndexVec<mir::Local, LocalKind>,
 }