cmd/compile/internal/syntax: remove dependency on cmd/internal/src

For dependency reasons, the data structure implementing source
positions in the compiler is in cmd/internal/src. It contains
highly compiler specific details (e.g. inlining index).

This change introduces a parallel but simpler position
representation, defined in the syntax package, which removes
that package's dependency on cmd/internal/src, and also removes
the need to deal with certain filename-specific operations
(defined by the needs of the compiler) in the syntax package.
As a result, the syntax package becomes again a compiler-
independent, stand-alone package that at some point might
replace (or augment) the existing top-level go/* syntax-related
packages.

Additionally, line directives that update column numbers
are now correctly tracked through the syntax package, with
additional tests added. (The respective changes also need to
be made in cmd/internal/src; i.e., the compiler accepts but
still ignores column numbers in line directives.)

This change comes at the cost of a new position translation
step, but that step is cheap because it only needs to do real
work if the position base changed (i.e., if there is a new file,
or new line directive).

There is no noticeable impact on overall compiler performance
measured with `compilebench -count 5 -alloc`:

name       old time/op       new time/op       delta
Template         220ms ± 8%        228ms ±18%    ~     (p=0.548 n=5+5)
Unicode          119ms ±11%        113ms ± 5%    ~     (p=0.056 n=5+5)
GoTypes          684ms ± 6%        677ms ± 3%    ~     (p=0.841 n=5+5)
Compiler         3.19s ± 7%        3.01s ± 1%    ~     (p=0.095 n=5+5)
SSA              7.92s ± 8%        7.79s ± 1%    ~     (p=0.690 n=5+5)
Flate            141ms ± 7%        139ms ± 4%    ~     (p=0.548 n=5+5)
GoParser         173ms ±12%        171ms ± 4%    ~     (p=1.000 n=5+5)
Reflect          417ms ± 5%        411ms ± 3%    ~     (p=0.548 n=5+5)
Tar              205ms ± 5%        198ms ± 2%    ~     (p=0.690 n=5+5)
XML              232ms ± 4%        229ms ± 4%    ~     (p=0.690 n=5+5)
StdCmd           28.7s ± 5%        28.2s ± 2%    ~     (p=0.421 n=5+5)

name       old user-time/op  new user-time/op  delta
Template         269ms ± 4%        265ms ± 5%    ~     (p=0.421 n=5+5)
Unicode          153ms ± 7%        149ms ± 3%    ~     (p=0.841 n=5+5)
GoTypes          850ms ± 7%        862ms ± 4%    ~     (p=0.841 n=5+5)
Compiler         4.01s ± 5%        3.86s ± 0%    ~     (p=0.190 n=5+4)
SSA              10.9s ± 4%        10.8s ± 2%    ~     (p=0.548 n=5+5)
Flate            166ms ± 7%        167ms ± 6%    ~     (p=1.000 n=5+5)
GoParser         204ms ± 8%        206ms ± 7%    ~     (p=0.841 n=5+5)
Reflect          514ms ± 5%        508ms ± 4%    ~     (p=0.548 n=5+5)
Tar              245ms ± 6%        244ms ± 3%    ~     (p=0.690 n=5+5)
XML              280ms ± 4%        278ms ± 4%    ~     (p=0.841 n=5+5)

name       old alloc/op      new alloc/op      delta
Template        37.9MB ± 0%       37.9MB ± 0%    ~     (p=0.841 n=5+5)
Unicode         28.8MB ± 0%       28.8MB ± 0%    ~     (p=0.841 n=5+5)
GoTypes          113MB ± 0%        113MB ± 0%    ~     (p=0.151 n=5+5)
Compiler         468MB ± 0%        468MB ± 0%  -0.01%  (p=0.032 n=5+5)
SSA             1.50GB ± 0%       1.50GB ± 0%    ~     (p=0.548 n=5+5)
Flate           24.4MB ± 0%       24.4MB ± 0%    ~     (p=1.000 n=5+5)
GoParser        30.7MB ± 0%       30.7MB ± 0%    ~     (p=1.000 n=5+5)
Reflect         76.5MB ± 0%       76.5MB ± 0%    ~     (p=0.548 n=5+5)
Tar             38.9MB ± 0%       38.9MB ± 0%    ~     (p=0.222 n=5+5)
XML             41.6MB ± 0%       41.6MB ± 0%    ~     (p=0.548 n=5+5)

name       old allocs/op     new allocs/op     delta
Template          382k ± 0%         382k ± 0%  +0.01%  (p=0.008 n=5+5)
Unicode           343k ± 0%         343k ± 0%    ~     (p=0.841 n=5+5)
GoTypes          1.19M ± 0%        1.19M ± 0%  +0.01%  (p=0.008 n=5+5)
Compiler         4.53M ± 0%        4.53M ± 0%  +0.03%  (p=0.008 n=5+5)
SSA              12.4M ± 0%        12.4M ± 0%  +0.00%  (p=0.008 n=5+5)
Flate             235k ± 0%         235k ± 0%    ~     (p=0.079 n=5+5)
GoParser          318k ± 0%         318k ± 0%    ~     (p=0.730 n=5+5)
Reflect           978k ± 0%         978k ± 0%    ~     (p=1.000 n=5+5)
Tar               393k ± 0%         393k ± 0%    ~     (p=0.056 n=5+5)
XML               405k ± 0%         405k ± 0%    ~     (p=0.548 n=5+5)

name       old text-bytes    new text-bytes    delta
HelloSize        672kB ± 0%        672kB ± 0%    ~     (all equal)
CmdGoSize       7.12MB ± 0%       7.12MB ± 0%    ~     (all equal)

name       old data-bytes    new data-bytes    delta
HelloSize        133kB ± 0%        133kB ± 0%    ~     (all equal)
CmdGoSize        390kB ± 0%        390kB ± 0%    ~     (all equal)

name       old exe-bytes     new exe-bytes     delta
HelloSize       1.07MB ± 0%       1.07MB ± 0%    ~     (all equal)
CmdGoSize       11.2MB ± 0%       11.2MB ± 0%    ~     (all equal)

Passes toolstash compare.

For #22662.

Change-Id: I19edb53dd9675af57f7122cb7dba2a6d8bdcc3da
Reviewed-on: https://go-review.googlesource.com/94515
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 7 insertions, 10 deletions

diff --git a/src/cmd/compile/internal/syntax/branches.go b/src/cmd/compile/internal/syntax/branches.go
index 2fd97a4a67..a03e2734d2 100644
--- a/src/cmd/compile/internal/syntax/branches.go
+++ b/src/cmd/compile/internal/syntax/branches.go
@@ -4,10 +4,7 @@
 
 package syntax
 
-import (
-	"cmd/internal/src"
-	"fmt"
-)
+import "fmt"
 
 // TODO(gri) consider making this part of the parser code
 
@@ -62,11 +59,11 @@ type label struct {
 
 type block struct {
 	parent *block       // immediately enclosing block, or nil
-	start  src.Pos      // start of block
+	start  Pos          // start of block
 	lstmt  *LabeledStmt // labeled statement associated with this block, or nil
 }
 
-func (ls *labelScope) err(pos src.Pos, format string, args ...interface{}) {
+func (ls *labelScope) err(pos Pos, format string, args ...interface{}) {
 	ls.errh(Error{pos, fmt.Sprintf(format, args...)})
 }
 
@@ -132,14 +129,14 @@ type targets struct {
 // list of unresolved (forward) gotos. parent is the immediately enclosing
 // block (or nil), ctxt provides information about the enclosing statements,
 // and lstmt is the labeled statement associated with this block, or nil.
-func (ls *labelScope) blockBranches(parent *block, ctxt targets, lstmt *LabeledStmt, start src.Pos, body []Stmt) []*BranchStmt {
+func (ls *labelScope) blockBranches(parent *block, ctxt targets, lstmt *LabeledStmt, start Pos, body []Stmt) []*BranchStmt {
 	b := &block{parent: parent, start: start, lstmt: lstmt}
 
-	var varPos src.Pos
+	var varPos Pos
 	var varName Expr
 	var fwdGotos, badGotos []*BranchStmt
 
-	recordVarDecl := func(pos src.Pos, name Expr) {
+	recordVarDecl := func(pos Pos, name Expr) {
 		varPos = pos
 		varName = name
 		// Any existing forward goto jumping over the variable
@@ -160,7 +157,7 @@ func (ls *labelScope) blockBranches(parent *block, ctxt targets, lstmt *LabeledS
 		return false
 	}
 
-	innerBlock := func(ctxt targets, start src.Pos, body []Stmt) {
+	innerBlock := func(ctxt targets, start Pos, body []Stmt) {
 		// Unresolved forward gotos from the inner block
 		// become forward gotos for the current block.
 		fwdGotos = append(fwdGotos, ls.blockBranches(b, ctxt, lstmt, start, body)...)