shrink mir::Statement to 40 bytes

[panstromek]

We do this by using (old-style) ThinVec for storing debuginfo.

From what I can tell using some basic eprintln! measurements, the debuginfos collection is almost always empty.

[panstromek]

@bors try @rust-timer queue

[rust-log-analyzer]

The job tidy failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

Diff in /checkout/compiler/rustc_middle/src/mir/statement.rs:1053:
     pub fn is_empty(&self) -> bool {
         match &self.0 {
             None => true,
-            Some(v) => v.is_empty()
+            Some(v) => v.is_empty(),
         }
     }
 
Diff in /checkout/compiler/rustc_middle/src/mir/statement.rs:1088:
     pub fn as_mut_slice(&mut self) -> &mut [StmtDebugInfo<'tcx>] {
         match self.0.as_mut() {
             None => &mut [],
-            Some(items) => items.as_mut_slice()
+            Some(items) => items.as_mut_slice(),
         }
     }
 
Diff in /checkout/compiler/rustc_middle/src/mir/statement.rs:1095:
     pub fn retain_locals(&mut self, locals: &DenseBitSet<Local>) {
         match &mut self.0 {
             None => (),
-            Some(items) => {
-                items.retain(|debuginfo| match debuginfo {
-                    StmtDebugInfo::AssignRef(local, _) | StmtDebugInfo::InvalidAssign(local) => {
-                        locals.contains(*local)
-                    }
-                })
-            }
+            Some(items) => items.retain(|debuginfo| match debuginfo {
+                StmtDebugInfo::AssignRef(local, _) | StmtDebugInfo::InvalidAssign(local) => {
+                    locals.contains(*local)
+                }
+            }),
         }
     }
 }

[rust-bors]

☀️ Try build successful (CI)
Build commit: 5aa011a (5aa011acd7e9ca4e63fb318d6e94dbf24e019ec7)
Base parent: 561ea2b (561ea2bfa3022226082e2db39d6ccb241e9e34bc)

[rust-timer]

Finished benchmarking commit (5aa011a): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.2%, 0.3%]	5
Regressions ❌ (secondary)	0.5%	[0.2%, 0.7%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.1%	[-0.2%, -0.1%]	3
All ❌✅ (primary)	0.3%	[0.2%, 0.3%]	5

Max RSS (memory usage)

Results (primary -1.4%, secondary -2.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.7%	[2.7%, 2.7%]	1
Improvements ✅ (primary)	-1.4%	[-2.5%, -0.6%]	37
Improvements ✅ (secondary)	-2.5%	[-4.1%, -1.0%]	31
All ❌✅ (primary)	-1.4%	[-2.5%, -0.6%]	37

Cycles

Results (primary -2.9%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.9%	[-2.9%, -2.9%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.9%	[-2.9%, -2.9%]	1

Binary size

Results (primary 0.0%, secondary 0.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.0%	[0.0%, 0.1%]	2
Regressions ❌ (secondary)	0.0%	[0.0%, 0.1%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[0.0%, 0.1%]	2

Bootstrap: 489.147s -> 487.269s (-0.38%)
Artifact size: 388.47 MiB -> 388.44 MiB (-0.01%)

[panstromek]

Good Max RSS numbers, but I'm a bit confused by the unicode-normalization icount result. Debug-IncrFull is the one I was testing this on initially and it never actually pushes anything into the debuginfos list. Maybe I'm looking into this incorrectly, I'll try to figure out what's going on there.