Auto merge of #36296 - nagisa:pass-timing, r=eddyb

Count and report time taken by MIR passes

There’s some desire for deeper introspectability into what MIR passes cost us.

-Z time-passes after this PR:

```
   Compiling test_shim v0.1.0 (file:///home/nagisa/Documents/rust/rust/src/rustc/test_shim)
time: 0.000; rss: 29MB	parsing
time: 0.000; rss: 29MB	configuration
time: 0.000; rss: 29MB	recursion limit
time: 0.000; rss: 29MB	crate injection
time: 0.000; rss: 29MB	plugin loading
time: 0.000; rss: 29MB	plugin registration
time: 0.032; rss: 54MB	expansion
time: 0.000; rss: 54MB	maybe building test harness
time: 0.000; rss: 54MB	assigning node ids
time: 0.000; rss: 54MB	checking for inline asm in case the target doesn't support it
time: 0.000; rss: 54MB	complete gated feature checking
time: 0.000; rss: 54MB	collecting defs
time: 0.004; rss: 54MB	external crate/lib resolution
time: 0.000; rss: 54MB	early lint checks
time: 0.000; rss: 54MB	AST validation
time: 0.001; rss: 54MB	name resolution
time: 0.000; rss: 54MB	lowering ast -> hir
time: 0.000; rss: 56MB	indexing hir
time: 0.000; rss: 56MB	attribute checking
time: 0.000; rss: 56MB	language item collection
time: 0.000; rss: 56MB	lifetime resolution
time: 0.000; rss: 56MB	looking for entry point
time: 0.000; rss: 56MB	looking for plugin registrar
time: 0.000; rss: 56MB	region resolution
time: 0.000; rss: 56MB	loop checking
time: 0.000; rss: 56MB	static item recursion checking
time: 0.000; rss: 56MB	compute_incremental_hashes_map
time: 0.000; rss: 56MB	load_dep_graph
time: 0.000; rss: 56MB	type collecting
time: 0.000; rss: 56MB	variance inference
time: 0.011; rss: 59MB	coherence checking
time: 0.000; rss: 59MB	wf checking
time: 0.000; rss: 59MB	item-types checking
time: 0.000; rss: 59MB	item-bodies checking
time: 0.000; rss: 59MB	drop-impl checking
time: 0.000; rss: 59MB	const checking
time: 0.000; rss: 59MB	privacy checking
time: 0.000; rss: 59MB	stability index
time: 0.000; rss: 59MB	intrinsic checking
time: 0.000; rss: 59MB	effect checking
time: 0.000; rss: 59MB	match checking
time: 0.000; rss: 59MB	liveness checking
time: 0.000; rss: 59MB	rvalue checking
time: 0.000; rss: 59MB	MIR dump
  time: 0.000; rss: 59MB	SimplifyCfg
  time: 0.000; rss: 59MB	QualifyAndPromoteConstants
  time: 0.000; rss: 59MB	TypeckMir
  time: 0.000; rss: 59MB	SimplifyBranches
  time: 0.000; rss: 59MB	SimplifyCfg
time: 0.000; rss: 59MB	MIR passes
time: 0.000; rss: 59MB	borrow checking
time: 0.000; rss: 59MB	reachability checking
time: 0.000; rss: 59MB	death checking
time: 0.000; rss: 59MB	stability checking
time: 0.000; rss: 59MB	unused lib feature checking
time: 0.000; rss: 59MB	lint checking
time: 0.000; rss: 59MB	resolving dependency formats
  time: 0.000; rss: 59MB	NoLandingPads
  time: 0.000; rss: 59MB	SimplifyCfg
  time: 0.000; rss: 59MB	EraseRegions
  time: 0.000; rss: 59MB	AddCallGuards
  time: 0.000; rss: 59MB	ElaborateDrops
  time: 0.000; rss: 59MB	NoLandingPads
  time: 0.000; rss: 59MB	SimplifyCfg
  time: 0.000; rss: 59MB	Deaggregator
  time: 0.000; rss: 59MB	AddCallGuards
  time: 0.000; rss: 59MB	PreTrans
time: 0.000; rss: 59MB	Prepare MIR codegen passes
  time: 0.000; rss: 59MB	write metadata
  time: 0.000; rss: 61MB	translation item collection
  time: 0.000; rss: 61MB	codegen unit partitioning
  time: 0.000; rss: 61MB	internalize symbols
time: 0.007; rss: 61MB	translation
time: 0.000; rss: 61MB	assert dep graph
time: 0.000; rss: 61MB	serialize dep graph
time: 0.000; rss: 61MB	llvm function passes [2]
time: 0.000; rss: 61MB	llvm function passes [3]
time: 0.000; rss: 61MB	llvm function passes [1]
time: 0.000; rss: 61MB	llvm function passes [0]
time: 0.000; rss: 61MB	llvm module passes [2]
time: 0.000; rss: 61MB	llvm module passes [1]
time: 0.000; rss: 61MB	llvm module passes [0]
time: 0.000; rss: 61MB	llvm module passes [3]
time: 0.001; rss: 62MB	codegen passes [1]
time: 0.001; rss: 62MB	codegen passes [2]
time: 0.001; rss: 62MB	codegen passes [0]
time: 0.001; rss: 62MB	codegen passes [3]
time: 0.001; rss: 63MB	codegen passes [1]
time: 0.005; rss: 63MB	LLVM passes
time: 0.000; rss: 63MB	serialize work products
time: 0.001; rss: 63MB	linking
```

r? @eddyb or @nikomatsakis

cc @nrc, @Mark-Simulacrum

src/librustc/mir/transform.rs

@@ -15,7 +15,9 @@ use mir::mir_map::MirMap;
 use mir::repr::{Mir, Promoted};
 use ty::TyCtxt;
 use syntax::ast::NodeId;
+use util::common::time;
 
+use std::borrow::Cow;
 use std::fmt;
 
 /// Where a specific Mir comes from.
@@ -72,12 +74,12 @@ impl<'a, 'tcx> MirSource {
 /// Various information about pass.
 pub trait Pass {
     // fn should_run(Session) to check if pass should run?
-    fn name(&self) -> &str {
+    fn name<'a>(&self) -> Cow<'static, str> {
         let name = unsafe { ::std::intrinsics::type_name::<Self>() };
         if let Some(tail) = name.rfind(":") {
-            &name[tail+1..]
+            Cow::from(&name[tail+1..])
         } else {
-            name
+            Cow::from(name)
         }
     }
     fn disambiguator<'a>(&'a self) -> Option<Box<fmt::Display+'a>> { None }
@@ -162,11 +164,10 @@ impl<'a, 'tcx> Passes {
     }
 
     pub fn run_passes(&mut self, tcx: TyCtxt<'a, 'tcx, 'tcx>, map: &mut MirMap<'tcx>) {
-        for pass in &mut self.plugin_passes {
-            pass.run_pass(tcx, map, &mut self.pass_hooks);
-        }
-        for pass in &mut self.passes {
-            pass.run_pass(tcx, map, &mut self.pass_hooks);
+        let Passes { ref mut passes, ref mut plugin_passes, ref mut pass_hooks } = *self;
+        for pass in plugin_passes.iter_mut().chain(passes.iter_mut()) {
+            time(tcx.sess.time_passes(), &*pass.name(),
+                 || pass.run_pass(tcx, map, pass_hooks));
         }
     }
 

src/librustc_mir/transform/dump_mir.rs

@@ -26,7 +26,7 @@ impl<'b, 'tcx> MirPass<'tcx> for Marker<'b> {
 }
 
 impl<'b> Pass for Marker<'b> {
-    fn name(&self) -> &str { self.0 }
+    fn name(&self) -> ::std::borrow::Cow<'static, str> { String::from(self.0).into() }
 }
 
 pub struct Disambiguator<'a> {
@@ -58,7 +58,7 @@ impl<'tcx> MirPassHook<'tcx> for DumpMir {
     {
         pretty::dump_mir(
             tcx,
-            pass.name(),
+            &*pass.name(),
             &Disambiguator {
                 pass: pass,
                 is_after: is_after

src/librustc_mir/transform/simplify_branches.rs

@@ -62,5 +62,5 @@ impl<'l> Pass for SimplifyBranches<'l> {
     }
 
     // avoid calling `type_name` - it contains `<'static>`
-    fn name(&self) -> &str { "SimplifyBranches" }
+    fn name(&self) -> ::std::borrow::Cow<'static, str> { "SimplifyBranches".into() }
 }

src/librustc_mir/transform/simplify_cfg.rs

@@ -64,7 +64,7 @@ impl<'l> Pass for SimplifyCfg<'l> {
     }
 
     // avoid calling `type_name` - it contains `<'static>`
-    fn name(&self) -> &str { "SimplifyCfg" }
+    fn name(&self) -> ::std::borrow::Cow<'static, str> { "SimplifyCfg".into() }
 }
 
 pub struct CfgSimplifier<'a, 'tcx: 'a> {