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[C++] Save memory/time when folding CONSTRUCTORs

Message ID alpine.LSU.2.20.1702011630360.12993@r111.fhfr.qr
State New
Headers show

Commit Message

Richard Biener Feb. 1, 2017, 3:31 p.m. UTC 
On Wed, 1 Feb 2017, Nathan Sidwell wrote:

> On 02/01/2017 10:18 AM, Richard Biener wrote:
> 
> > True.  Updated patch below.
> > 
> > Richard.
> > 
> > 2017-02-01  Richard Biener  <rguenther@suse.de>
> > 
> > 	PR cp/14179
> > 	cp/
> > 	* cp-gimplify.c (cp_fold): When folding a CONSTRUCTOR copy
> > 	it lazily on the first changed element only and copy it
> > 	fully upfront, only storing changed elements.
> 
> Looks good, with the tweak Jakub noticed.

And one more tweak, I have to free it for the error_mark_case.
(vec_free sets nelts to NULL)

Richard.

2017-02-01  Richard Biener  <rguenther@suse.de>

	PR cp/14179
	cp/
	* cp-gimplify.c (cp_fold): When folding a CONSTRUCTOR copy
	it lazily on the first changed element only and copy it
	fully upfront, only storing changed elements.
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Patch

Index: gcc/cp/cp-gimplify.c
===================================================================
--- gcc/cp/cp-gimplify.c	(revision 245096)
+++ gcc/cp/cp-gimplify.c	(working copy)
@@ -2358,30 +2358,26 @@  cp_fold (tree x)
       {
 	unsigned i;
 	constructor_elt *p;
-	bool changed = false;
 	vec<constructor_elt, va_gc> *elts = CONSTRUCTOR_ELTS (x);
 	vec<constructor_elt, va_gc> *nelts = NULL;
-	vec_safe_reserve (nelts, vec_safe_length (elts));
 	FOR_EACH_VEC_SAFE_ELT (elts, i, p)
 	  {
 	    tree op = cp_fold (p->value);
-	    constructor_elt e = { p->index, op };
-	    nelts->quick_push (e);
 	    if (op != p->value)
 	      {
 		if (op == error_mark_node)
 		  {
 		    x = error_mark_node;
-		    changed = false;
+		    vec_free (nelts);
 		    break;
 		  }
-		changed = true;
+		if (nelts == NULL)
+		  nelts = elts->copy ();
+		(*nelts)[i].value = op;
 	      }
 	  }
-	if (changed)
+	if (nelts)
 	  x = build_constructor (TREE_TYPE (x), nelts);
-	else
-	  vec_free (nelts);
 	break;
       }
     case TREE_VEC: