Auto merge of #44249 - pnkfelix:debugflag-emit-end-regions, r=arielb1

Debugflag: -Z emit-end-regions

 Skip EndRegion emission by default. Use `-Z emit-end-regions` to reenable it.

The main intent is to fix cases where `EndRegion` emission is believed to be causing excess peak memory pressure.

It may also be a welcome change to people inspecting the MIR output who find the EndRegions to be a distraction.

(In later follow-up PR's I will put in safe-guards against using the current mir-borrowck without enabling `EndRegion` emission. But I wanted this PR to be minimal, in part because we may wish to backport it to the beta channel if we find that it reduces peak memory usage significantly.)

15 files changed, 39 insertions, 26 deletions

diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index b538c6a6eca..577c905a1d5 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -919,6 +919,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "when debug-printing compiler state, do not include spans"), // o/w tests have closure@path
     identify_regions: bool = (false, parse_bool, [UNTRACKED],
         "make unnamed regions display as '# (where # is some non-ident unique id)"),
+    emit_end_regions: bool = (false, parse_bool, [UNTRACKED],
+        "emit EndRegion as part of MIR; enable transforms that solely process EndRegion"),
     borrowck_mir: bool = (false, parse_bool, [UNTRACKED],
         "implicitly treat functions as if they have `#[rustc_mir_borrowck]` attribute"),
     time_passes: bool = (false, parse_bool, [UNTRACKED],
diff --git a/src/librustc/session/mod.rs b/src/librustc/session/mod.rs
index 823a637c7e0..129a9f55750 100644
--- a/src/librustc/session/mod.rs
+++ b/src/librustc/session/mod.rs
@@ -410,6 +410,10 @@ impl Session {
     pub fn print_llvm_passes(&self) -> bool {
         self.opts.debugging_opts.print_llvm_passes
     }
+    pub fn emit_end_regions(&self) -> bool {
+        self.opts.debugging_opts.emit_end_regions ||
+            (self.opts.debugging_opts.mir_emit_validate > 0)
+    }
     pub fn lto(&self) -> bool {
         self.opts.cg.lto
     }
diff --git a/src/librustc_mir/build/cfg.rs b/src/librustc_mir/build/cfg.rs
index d77fe5170e0..a6e31bcddd2 100644
--- a/src/librustc_mir/build/cfg.rs
+++ b/src/librustc_mir/build/cfg.rs
@@ -16,6 +16,7 @@
 use build::CFG;
 use rustc::middle::region;
 use rustc::mir::*;
+use rustc::ty;
 
 impl<'tcx> CFG<'tcx> {
     pub fn block_data(&self, blk: BasicBlock) -> &BasicBlockData<'tcx> {
@@ -44,14 +45,17 @@ impl<'tcx> CFG<'tcx> {
         self.block_data_mut(block).statements.push(statement);
     }
 
-    pub fn push_end_region(&mut self,
-                           block: BasicBlock,
-                           source_info: SourceInfo,
-                           region_scope: region::Scope) {
-        self.push(block, Statement {
-            source_info,
-            kind: StatementKind::EndRegion(region_scope),
-        });
+    pub fn push_end_region<'a, 'gcx:'a+'tcx>(&mut self,
+                                             tcx: ty::TyCtxt<'a, 'gcx, 'tcx>,
+                                             block: BasicBlock,
+                                             source_info: SourceInfo,
+                                             region_scope: region::Scope) {
+        if tcx.sess.emit_end_regions() {
+            self.push(block, Statement {
+                source_info,
+                kind: StatementKind::EndRegion(region_scope),
+            });
+        }
     }
 
     pub fn push_assign(&mut self,
diff --git a/src/librustc_mir/build/scope.rs b/src/librustc_mir/build/scope.rs
index ed598c876f3..c08620c1e41 100644
--- a/src/librustc_mir/build/scope.rs
+++ b/src/librustc_mir/build/scope.rs
@@ -89,7 +89,7 @@ should go to.
 
 use build::{BlockAnd, BlockAndExtension, Builder, CFG};
 use rustc::middle::region;
-use rustc::ty::Ty;
+use rustc::ty::{Ty, TyCtxt};
 use rustc::mir::*;
 use rustc::mir::transform::MirSource;
 use syntax_pos::{Span};
@@ -359,7 +359,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                                           self.arg_count,
                                           false));
 
-        self.cfg.push_end_region(block, region_scope.1, scope.region_scope);
+        self.cfg.push_end_region(self.hir.tcx(), block, region_scope.1, scope.region_scope);
         block.unit()
     }
 
@@ -414,7 +414,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                                               false));
 
             // End all regions for scopes out of which we are breaking.
-            self.cfg.push_end_region(block, region_scope.1, scope.region_scope);
+            self.cfg.push_end_region(self.hir.tcx(), block, region_scope.1, scope.region_scope);
         }
         }
         let scope = &self.scopes[len - scope_count];
@@ -463,7 +463,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                                               true));
 
             // End all regions for scopes out of which we are breaking.
-            self.cfg.push_end_region(block, src_info, scope.region_scope);
+            self.cfg.push_end_region(self.hir.tcx(), block, src_info, scope.region_scope);
         }
 
         self.cfg.terminate(block, src_info, TerminatorKind::GeneratorDrop);
@@ -694,7 +694,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
         };
 
         for scope in scopes.iter_mut() {
-            target = build_diverge_scope(cfg, scope.region_scope_span,
+            target = build_diverge_scope(self.hir.tcx(), cfg, scope.region_scope_span,
                                          scope, target, generator_drop);
         }
         Some(target)
@@ -831,7 +831,8 @@ fn build_scope_drops<'tcx>(cfg: &mut CFG<'tcx>,
     block.unit()
 }
 
-fn build_diverge_scope<'a, 'gcx, 'tcx>(cfg: &mut CFG<'tcx>,
+fn build_diverge_scope<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
+                                       cfg: &mut CFG<'tcx>,
                                        span: Span,
                                        scope: &mut Scope<'tcx>,
                                        mut target: BasicBlock,
@@ -893,7 +894,7 @@ fn build_diverge_scope<'a, 'gcx, 'tcx>(cfg: &mut CFG<'tcx>,
     // becomes trivial goto after pass that removes all EndRegions.)
     {
         let block = cfg.start_new_cleanup_block();
-        cfg.push_end_region(block, source_info(span), scope.region_scope);
+        cfg.push_end_region(tcx, block, source_info(span), scope.region_scope);
         cfg.terminate(block, source_info(span), TerminatorKind::Goto { target: target });
         target = block
     }
diff --git a/src/librustc_mir/transform/clean_end_regions.rs b/src/librustc_mir/transform/clean_end_regions.rs
index 55a16b2f391..a6750f400ba 100644
--- a/src/librustc_mir/transform/clean_end_regions.rs
+++ b/src/librustc_mir/transform/clean_end_regions.rs
@@ -39,9 +39,11 @@ struct DeleteTrivialEndRegions<'a> {
 
 impl MirPass for CleanEndRegions {
     fn run_pass<'a, 'tcx>(&self,
-                          _tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                          tcx: TyCtxt<'a, 'tcx, 'tcx>,
                           _source: MirSource,
                           mir: &mut Mir<'tcx>) {
+        if !tcx.sess.emit_end_regions() { return; }
+
         let mut gather = GatherBorrowedRegions {
             seen_regions: FxHashSet()
         };
diff --git a/src/test/mir-opt/end_region_1.rs b/src/test/mir-opt/end_region_1.rs
index 54409d3543e..9c8cfc0ab20 100644
--- a/src/test/mir-opt/end_region_1.rs
+++ b/src/test/mir-opt/end_region_1.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z identify_regions
+// compile-flags: -Z identify_regions -Z emit-end-regions
 // ignore-tidy-linelength
 
 // This is just about the simplest program that exhibits an EndRegion.
diff --git a/src/test/mir-opt/end_region_2.rs b/src/test/mir-opt/end_region_2.rs
index b37bd4188d9..6a4e209a14b 100644
--- a/src/test/mir-opt/end_region_2.rs
+++ b/src/test/mir-opt/end_region_2.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z identify_regions
+// compile-flags: -Z identify_regions -Z emit-end-regions
 // ignore-tidy-linelength
 
 // We will EndRegion for borrows in a loop that occur before break but
diff --git a/src/test/mir-opt/end_region_3.rs b/src/test/mir-opt/end_region_3.rs
index be9fc579ab6..cb1d45e37c8 100644
--- a/src/test/mir-opt/end_region_3.rs
+++ b/src/test/mir-opt/end_region_3.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z identify_regions
+// compile-flags: -Z identify_regions -Z emit-end-regions
 // ignore-tidy-linelength
 
 // Binding the borrow's subject outside the loop does not increase the
diff --git a/src/test/mir-opt/end_region_4.rs b/src/test/mir-opt/end_region_4.rs
index 58ce1ed5b84..b714b6bc55b 100644
--- a/src/test/mir-opt/end_region_4.rs
+++ b/src/test/mir-opt/end_region_4.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z identify_regions
+// compile-flags: -Z identify_regions -Z emit-end-regions
 // ignore-tidy-linelength
 
 // Unwinding should EndRegion for in-scope borrows: Direct borrows.
diff --git a/src/test/mir-opt/end_region_5.rs b/src/test/mir-opt/end_region_5.rs
index be62a5473a6..a4c53675b9c 100644
--- a/src/test/mir-opt/end_region_5.rs
+++ b/src/test/mir-opt/end_region_5.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z identify_regions -Z span_free_formats
+// compile-flags: -Z identify_regions -Z span_free_formats -Z emit-end-regions
 // ignore-tidy-linelength
 
 // Unwinding should EndRegion for in-scope borrows: Borrowing via by-ref closure.
diff --git a/src/test/mir-opt/end_region_6.rs b/src/test/mir-opt/end_region_6.rs
index 23b92583a11..daa94769430 100644
--- a/src/test/mir-opt/end_region_6.rs
+++ b/src/test/mir-opt/end_region_6.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z identify_regions -Z span_free_formats
+// compile-flags: -Z identify_regions -Z span_free_formats -Z emit-end-regions
 // ignore-tidy-linelength
 
 // Unwinding should EndRegion for in-scope borrows: 2nd borrow within by-ref closure.
diff --git a/src/test/mir-opt/end_region_7.rs b/src/test/mir-opt/end_region_7.rs
index ee0615f2bb3..9feacd04fe0 100644
--- a/src/test/mir-opt/end_region_7.rs
+++ b/src/test/mir-opt/end_region_7.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z identify_regions -Z span_free_formats
+// compile-flags: -Z identify_regions -Z span_free_formats -Z emit-end-regions
 // ignore-tidy-linelength
 
 // Unwinding should EndRegion for in-scope borrows: Borrow of moved data.
diff --git a/src/test/mir-opt/end_region_8.rs b/src/test/mir-opt/end_region_8.rs
index ef184e39c00..30dda7a4062 100644
--- a/src/test/mir-opt/end_region_8.rs
+++ b/src/test/mir-opt/end_region_8.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z identify_regions -Z span_free_formats
+// compile-flags: -Z identify_regions -Z span_free_formats -Z emit-end-regions
 // ignore-tidy-linelength
 
 // Unwinding should EndRegion for in-scope borrows: Move of borrow into closure.
diff --git a/src/test/mir-opt/end_region_9.rs b/src/test/mir-opt/end_region_9.rs
index 719bc3ff9dd..bbfdc0e77a8 100644
--- a/src/test/mir-opt/end_region_9.rs
+++ b/src/test/mir-opt/end_region_9.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z identify_regions -Z span_free_formats
+// compile-flags: -Z identify_regions -Z span_free_formats -Z emit-end-regions
 // ignore-tidy-linelength
 
 // This test models a scenario that arielb1 found during review.
diff --git a/src/test/mir-opt/issue-43457.rs b/src/test/mir-opt/issue-43457.rs
index 2a36672a457..3f0f5068577 100644
--- a/src/test/mir-opt/issue-43457.rs
+++ b/src/test/mir-opt/issue-43457.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z identify_regions -Z span_free_formats
+// compile-flags: -Z identify_regions -Z span_free_formats -Z emit-end-regions
 // ignore-tidy-linelength
 
 // Regression test for #43457: an `EndRegion` was missing from output