Auto merge of #37642 - nnethercote:no-HirVec-of-P, r=michaelwoerister

Change HirVec<P<T>> to HirVec<T> in hir:: Expr.

This PR changes data structures like this:
```
[ ExprArray | 8 | P ]
                  |
                  v
                  [ P | P | P | P | P | P | P | P ]
                    |
                    v
                    [ ExprTup | 2 | P ]
                                    |
                                    v
                                    [ P | P ]
                                      |
                                      v
                                      [ Expr ]
```
to this:
```
[ ExprArray | 8 | P ]
                  |
                  v
                  [ [ ExprTup | 2 | P ] | ... ]
                                    |
                                    v
                                    [ Expr | Expr ]
```
I thought this would be a win for #36799, and on a cut-down version of that workload this reduces the peak heap size (as measured by Massif) from 885 MiB to 875 MiB. However, the peak RSS as measured by `-Ztime-passes` and by `/usr/bin/time` increases by about 30 MiB.

I'm not sure why. Just look at the picture above -- the second data structure clearly takes up less space than the first. My best idea relates to unused elements in the slices. `HirVec<Expr>` is a typedef for `P<[Expr]>`. If there were any unused excess elements then I could see that memory usage would increase, because those excess elements are larger in `HirVec<Expr>` than in `HirVec<P<Expr>>`. But AIUI there are no such excess elements, and Massif's measurements corroborate that.

However, the two main creation points for these data structures are these lines from `lower_expr`:
```rust
        ExprKind::Vec(ref exprs) => {
            hir::ExprArray(exprs.iter().map(|x| self.lower_expr(x)).collect())
        }
        ExprKind::Tup(ref elts) => {
            hir::ExprTup(elts.iter().map(|x| self.lower_expr(x)).collect())
        }
```
I suspect what is happening is that temporary excess elements are created within the `collect` calls. The workload from #36799 has many 2-tuples and 3-tuples and when `Vec` gets doubled it goes from a capacity of 1 to 4, which would lead to excess elements. Though, having said that, `Vec::with_capacity` doesn't create excess AFAICT. So I'm not sure. What goes on inside `collect` is complex.

Anyway, in its current form this PR is a memory consumption regression and so not worth landing but I figured I'd post it in case anyone has additional insight.

Author: bors

src/librustc/cfg/construct.rs

@@ -299,15 +299,15 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
             }
 
             hir::ExprArray(ref elems) => {
-                self.straightline(expr, pred, elems.iter().map(|e| &**e))
+                self.straightline(expr, pred, elems.iter().map(|e| &*e))
             }
 
             hir::ExprCall(ref func, ref args) => {
-                self.call(expr, pred, &func, args.iter().map(|e| &**e))
+                self.call(expr, pred, &func, args.iter().map(|e| &*e))
             }
 
             hir::ExprMethodCall(.., ref args) => {
-                self.call(expr, pred, &args[0], args[1..].iter().map(|e| &**e))
+                self.call(expr, pred, &args[0], args[1..].iter().map(|e| &*e))
             }
 
             hir::ExprIndex(ref l, ref r) |
@@ -320,7 +320,7 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
             }
 
             hir::ExprTup(ref exprs) => {
-                self.straightline(expr, pred, exprs.iter().map(|e| &**e))
+                self.straightline(expr, pred, exprs.iter().map(|e| &*e))
             }
 
             hir::ExprStruct(_, ref fields, ref base) => {
@@ -353,8 +353,8 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
             }
 
             hir::ExprInlineAsm(_, ref outputs, ref inputs) => {
-                let post_outputs = self.exprs(outputs.iter().map(|e| &**e), pred);
-                let post_inputs = self.exprs(inputs.iter().map(|e| &**e), post_outputs);
+                let post_outputs = self.exprs(outputs.iter().map(|e| &*e), pred);
+                let post_inputs = self.exprs(inputs.iter().map(|e| &*e), post_outputs);
                 self.add_ast_node(expr.id, &[post_inputs])
             }
 

src/librustc/hir/lowering.rs

@@ -867,12 +867,12 @@ pub enum Expr_ {
     /// A `box x` expression.
     ExprBox(P<Expr>),
     /// An array (`[a, b, c, d]`)
-    ExprArray(HirVec<P<Expr>>),
+    ExprArray(HirVec<Expr>),
     /// A function call
     ///
     /// The first field resolves to the function itself (usually an `ExprPath`),
     /// and the second field is the list of arguments
-    ExprCall(P<Expr>, HirVec<P<Expr>>),
+    ExprCall(P<Expr>, HirVec<Expr>),
     /// A method call (`x.foo::<Bar, Baz>(a, b, c, d)`)
     ///
     /// The `Spanned<Name>` is the identifier for the method name.
@@ -885,9 +885,9 @@ pub enum Expr_ {
     ///
     /// Thus, `x.foo::<Bar, Baz>(a, b, c, d)` is represented as
     /// `ExprMethodCall(foo, [Bar, Baz], [x, a, b, c, d])`.
-    ExprMethodCall(Spanned<Name>, HirVec<P<Ty>>, HirVec<P<Expr>>),
+    ExprMethodCall(Spanned<Name>, HirVec<P<Ty>>, HirVec<Expr>),
     /// A tuple (`(a, b, c ,d)`)
-    ExprTup(HirVec<P<Expr>>),
+    ExprTup(HirVec<Expr>),
     /// A binary operation (For example: `a + b`, `a * b`)
     ExprBinary(BinOp, P<Expr>, P<Expr>),
     /// A unary operation (For example: `!x`, `*x`)
@@ -951,7 +951,7 @@ pub enum Expr_ {
     ExprRet(Option<P<Expr>>),
 
     /// Inline assembly (from `asm!`), with its outputs and inputs.
-    ExprInlineAsm(P<InlineAsm>, HirVec<P<Expr>>, HirVec<P<Expr>>),
+    ExprInlineAsm(P<InlineAsm>, HirVec<Expr>, HirVec<Expr>),
 
     /// A struct or struct-like variant literal expression.
     ///

src/librustc/hir/mod.rs

@@ -452,7 +452,7 @@ impl<'a> State<'a> {
         self.end()
     }
 
-    pub fn commasep_exprs(&mut self, b: Breaks, exprs: &[P<hir::Expr>]) -> io::Result<()> {
+    pub fn commasep_exprs(&mut self, b: Breaks, exprs: &[hir::Expr]) -> io::Result<()> {
         self.commasep_cmnt(b, exprs, |s, e| s.print_expr(&e), |e| e.span)
     }
 
@@ -1200,7 +1200,7 @@ impl<'a> State<'a> {
     }
 
 
-    fn print_call_post(&mut self, args: &[P<hir::Expr>]) -> io::Result<()> {
+    fn print_call_post(&mut self, args: &[hir::Expr]) -> io::Result<()> {
         self.popen()?;
         self.commasep_exprs(Inconsistent, args)?;
         self.pclose()
@@ -1218,10 +1218,10 @@ impl<'a> State<'a> {
         Ok(())
     }
 
-    fn print_expr_vec(&mut self, exprs: &[P<hir::Expr>]) -> io::Result<()> {
+    fn print_expr_vec(&mut self, exprs: &[hir::Expr]) -> io::Result<()> {
         self.ibox(indent_unit)?;
         word(&mut self.s, "[")?;
-        self.commasep_exprs(Inconsistent, &exprs[..])?;
+        self.commasep_exprs(Inconsistent, exprs)?;
         word(&mut self.s, "]")?;
         self.end()
     }
@@ -1274,24 +1274,24 @@ impl<'a> State<'a> {
         Ok(())
     }
 
-    fn print_expr_tup(&mut self, exprs: &[P<hir::Expr>]) -> io::Result<()> {
+    fn print_expr_tup(&mut self, exprs: &[hir::Expr]) -> io::Result<()> {
         self.popen()?;
-        self.commasep_exprs(Inconsistent, &exprs[..])?;
+        self.commasep_exprs(Inconsistent, exprs)?;
         if exprs.len() == 1 {
             word(&mut self.s, ",")?;
         }
         self.pclose()
     }
 
-    fn print_expr_call(&mut self, func: &hir::Expr, args: &[P<hir::Expr>]) -> io::Result<()> {
+    fn print_expr_call(&mut self, func: &hir::Expr, args: &[hir::Expr]) -> io::Result<()> {
         self.print_expr_maybe_paren(func)?;
         self.print_call_post(args)
     }
 
     fn print_expr_method_call(&mut self,
                               name: Spanned<ast::Name>,
                               tys: &[P<hir::Ty>],
-                              args: &[P<hir::Expr>])
+                              args: &[hir::Expr])
                               -> io::Result<()> {
         let base_args = &args[1..];
         self.print_expr(&args[0])?;
@@ -1340,7 +1340,7 @@ impl<'a> State<'a> {
                 self.print_expr(expr)?;
             }
             hir::ExprArray(ref exprs) => {
-                self.print_expr_vec(&exprs[..])?;
+                self.print_expr_vec(exprs)?;
             }
             hir::ExprRepeat(ref element, ref count) => {
                 self.print_expr_repeat(&element, &count)?;
@@ -1349,13 +1349,13 @@ impl<'a> State<'a> {
                 self.print_expr_struct(path, &fields[..], wth)?;
             }
             hir::ExprTup(ref exprs) => {
-                self.print_expr_tup(&exprs[..])?;
+                self.print_expr_tup(exprs)?;
             }
             hir::ExprCall(ref func, ref args) => {
-                self.print_expr_call(&func, &args[..])?;
+                self.print_expr_call(&func, args)?;
             }
             hir::ExprMethodCall(name, ref tys, ref args) => {
-                self.print_expr_method_call(name, &tys[..], &args[..])?;
+                self.print_expr_method_call(name, &tys[..], args)?;
             }
             hir::ExprBinary(op, ref lhs, ref rhs) => {
                 self.print_expr_binary(op, &lhs, &rhs)?;

src/librustc/hir/print.rs

@@ -327,7 +327,7 @@ impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
         self.delegate.consume(consume_id, consume_span, cmt, mode);
     }
 
-    fn consume_exprs(&mut self, exprs: &[P<hir::Expr>]) {
+    fn consume_exprs(&mut self, exprs: &[hir::Expr]) {
         for expr in exprs {
             self.consume_expr(&expr);
         }

src/librustc/middle/expr_use_visitor.rs

@@ -123,7 +123,6 @@ use std::io::prelude::*;
 use std::io;
 use std::rc::Rc;
 use syntax::ast::{self, NodeId};
-use syntax::ptr::P;
 use syntax::symbol::keywords;
 use syntax_pos::Span;
 
@@ -902,7 +901,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
         self.define_bindings_in_pat(&local.pat, succ)
     }
 
-    fn propagate_through_exprs(&mut self, exprs: &[P<Expr>], succ: LiveNode)
+    fn propagate_through_exprs(&mut self, exprs: &[Expr], succ: LiveNode)
                                -> LiveNode {
         exprs.iter().rev().fold(succ, |succ, expr| {
             self.propagate_through_expr(&expr, succ)
@@ -1087,7 +1086,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
           // Uninteresting cases: just propagate in rev exec order
 
           hir::ExprArray(ref exprs) => {
-            self.propagate_through_exprs(&exprs[..], succ)
+            self.propagate_through_exprs(exprs, succ)
           }
 
           hir::ExprRepeat(ref element, ref count) => {
@@ -1111,7 +1110,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
             } else {
                 succ
             };
-            let succ = self.propagate_through_exprs(&args[..], succ);
+            let succ = self.propagate_through_exprs(args, succ);
             self.propagate_through_expr(&f, succ)
           }
 
@@ -1124,11 +1123,11 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
             } else {
                 succ
             };
-            self.propagate_through_exprs(&args[..], succ)
+            self.propagate_through_exprs(args, succ)
           }
 
           hir::ExprTup(ref exprs) => {
-            self.propagate_through_exprs(&exprs[..], succ)
+            self.propagate_through_exprs(exprs, succ)
           }
 
           hir::ExprBinary(op, ref l, ref r) if op.node.is_lazy() => {

src/librustc/middle/liveness.rs

@@ -297,7 +297,7 @@ pub fn const_expr_to_pat<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                 _ => bug!()
             };
             let pats = args.iter()
-                           .map(|expr| const_expr_to_pat(tcx, &**expr, pat_id, span))
+                           .map(|expr| const_expr_to_pat(tcx, &*expr, pat_id, span))
                            .collect::<Result<_, _>>()?;
             PatKind::TupleStruct(path, pats, None)
         }

src/librustc_const_eval/eval.rs

@@ -17,7 +17,6 @@ use hir::print;
 use rustc::{infer, traits};
 use rustc::ty::{self, LvaluePreference, Ty};
 use syntax::symbol::Symbol;
-use syntax::ptr::P;
 use syntax_pos::Span;
 
 use rustc::hir;
@@ -46,7 +45,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
     pub fn check_call(&self,
                       call_expr: &'gcx hir::Expr,
                       callee_expr: &'gcx hir::Expr,
-                      arg_exprs: &'gcx [P<hir::Expr>],
+                      arg_exprs: &'gcx [hir::Expr],
                       expected: Expectation<'tcx>)
                       -> Ty<'tcx> {
         let original_callee_ty = self.check_expr(callee_expr);
@@ -189,7 +188,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
     fn confirm_builtin_call(&self,
                             call_expr: &hir::Expr,
                             callee_ty: Ty<'tcx>,
-                            arg_exprs: &'gcx [P<hir::Expr>],
+                            arg_exprs: &'gcx [hir::Expr],
                             expected: Expectation<'tcx>)
                             -> Ty<'tcx> {
         let error_fn_sig;
@@ -272,7 +271,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 
     fn confirm_deferred_closure_call(&self,
                                      call_expr: &hir::Expr,
-                                     arg_exprs: &'gcx [P<hir::Expr>],
+                                     arg_exprs: &'gcx [hir::Expr],
                                      expected: Expectation<'tcx>,
                                      fn_sig: ty::FnSig<'tcx>)
                                      -> Ty<'tcx> {
@@ -299,7 +298,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
     fn confirm_overloaded_call(&self,
                                call_expr: &hir::Expr,
                                callee_expr: &'gcx hir::Expr,
-                               arg_exprs: &'gcx [P<hir::Expr>],
+                               arg_exprs: &'gcx [hir::Expr],
                                expected: Expectation<'tcx>,
                                method_callee: ty::MethodCallee<'tcx>)
                                -> Ty<'tcx> {

src/librustc_typeck/check/callee.rs

@@ -2409,7 +2409,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                                    sp: Span,
                                    method_fn_ty: Ty<'tcx>,
                                    callee_expr: &'gcx hir::Expr,
-                                   args_no_rcvr: &'gcx [P<hir::Expr>],
+                                   args_no_rcvr: &'gcx [hir::Expr],
                                    tuple_arguments: TupleArgumentsFlag,
                                    expected: Expectation<'tcx>)
                                    -> Ty<'tcx> {
@@ -2448,7 +2448,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                             sp: Span,
                             fn_inputs: &[Ty<'tcx>],
                             expected_arg_tys: &[Ty<'tcx>],
-                            args: &'gcx [P<hir::Expr>],
+                            args: &'gcx [hir::Expr],
                             variadic: bool,
                             tuple_arguments: TupleArgumentsFlag) {
         let tcx = self.tcx;
@@ -2822,7 +2822,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
     fn check_method_call(&self,
                          expr: &'gcx hir::Expr,
                          method_name: Spanned<ast::Name>,
-                         args: &'gcx [P<hir::Expr>],
+                         args: &'gcx [hir::Expr],
                          tps: &[P<hir::Ty>],
                          expected: Expectation<'tcx>,
                          lvalue_pref: LvaluePreference) -> Ty<'tcx> {
@@ -3670,10 +3670,10 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             self.check_block_with_expected(&b, expected)
           }
           hir::ExprCall(ref callee, ref args) => {
-              self.check_call(expr, &callee, &args[..], expected)
+              self.check_call(expr, &callee, args, expected)
           }
           hir::ExprMethodCall(name, ref tps, ref args) => {
-              self.check_method_call(expr, name, &args[..], &tps[..], expected, lvalue_pref)
+              self.check_method_call(expr, name, args, &tps[..], expected, lvalue_pref)
           }
           hir::ExprCast(ref e, ref t) => {
             if let hir::TyArray(_, ref count_expr) = t.node {
@@ -3728,7 +3728,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 let result = if i == 0 {
                     self.try_coerce(e, e_ty, coerce_to)
                 } else {
-                    let prev_elems = || args[..i].iter().map(|e| &**e);
+                    let prev_elems = || args[..i].iter().map(|e| &*e);
                     self.try_find_coercion_lub(&cause, prev_elems, unified, e, e_ty)
                 };
 

src/librustc_typeck/check/mod.rs

@@ -613,19 +613,19 @@ impl<'a, 'gcx, 'tcx, 'v> Visitor<'v> for RegionCtxt<'a, 'gcx, 'tcx> {
             hir::ExprCall(ref callee, ref args) => {
                 if has_method_map {
                     self.constrain_call(expr, Some(&callee),
-                                        args.iter().map(|e| &**e), false);
+                                        args.iter().map(|e| &*e), false);
                 } else {
                     self.constrain_callee(callee.id, expr, &callee);
                     self.constrain_call(expr, None,
-                                        args.iter().map(|e| &**e), false);
+                                        args.iter().map(|e| &*e), false);
                 }
 
                 intravisit::walk_expr(self, expr);
             }
 
             hir::ExprMethodCall(.., ref args) => {
                 self.constrain_call(expr, Some(&args[0]),
-                                    args[1..].iter().map(|e| &**e), false);
+                                    args[1..].iter().map(|e| &*e), false);
 
                 intravisit::walk_expr(self, expr);
             }