OpenE2K/gcc
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

d: Missed RVO optimization with non-POD structs

Browse Source 
The D front-end semantic pass sometimes declares a temporary inside a
return expression.  This is now detected with the RESULT_DECL replacing
the temporary, allowing for RVO to be done.

	PR d/101273

gcc/d/ChangeLog:

	* toir.cc (IRVisitor::visit (ReturnStatement *)): Detect returns that
	use a temporary, and replace with return value.

gcc/testsuite/ChangeLog:

	* gdc.dg/torture/pr101273.d: New test.

(cherry picked from commit 152f4d0e4d3b524ce30d05f20e23a44b0dd29765)
This commit is contained in:
Iain Buclaw 2021-07-03 02:42:14 +02:00
parent a4f5e3962f
commit 46d1cb4c21
2 changed files with 69 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
gcc/d/toir.cc
View File

@ -1034,14 +1034,37 @@ public:
/* Detect a call to a constructor function, or if returning a struct
literal, write result directly into the return value. */
StructLiteralExp *sle = NULL;
bool using_rvo_p = false;
if (DotVarExp *dve = (s->exp->op == TOKcall
&& s->exp->isCallExp ()->e1->op == TOKdotvar
? s->exp->isCallExp ()->e1->isDotVarExp ()
: NULL))
{
sle = (dve->var->isCtorDeclaration ()
? dve->e1->isStructLiteralExp () : NULL);
if (dve->var->isCtorDeclaration ())
{
if (CommaExp *ce = dve->e1->isCommaExp ())
{
/* Temporary initialized inside a return expression, and
used as the return value. Replace it with the hidden
reference to allow RVO return. */
DeclarationExp *de = ce->e1->isDeclarationExp ();
VarExp *ve = ce->e2->isVarExp ();
if (de != NULL && ve != NULL
&& ve->var == de->declaration
&& ve->var->storage_class & STCtemp)
{
tree var = get_symbol_decl (ve->var);
TREE_ADDRESSABLE (var) = 1;
SET_DECL_VALUE_EXPR (var, decl);
DECL_HAS_VALUE_EXPR_P (var) = 1;
SET_DECL_LANG_NRVO (var, this->func_->shidden);
using_rvo_p = true;
}
}
else
sle = dve->e1->isStructLiteralExp ();
}
}
else
sle = s->exp->isStructLiteralExp ();
@ -1050,11 +1073,16 @@ public:
{
StructDeclaration *sd = type->baseElemOf ()->isTypeStruct ()->sym;
sle->sym = build_address (this->func_->shidden);
using_rvo_p = true;
/* Fill any alignment holes in the return slot using memset. */
if (!identity_compare_p (sd) || sd->isUnionDeclaration ())
add_stmt (build_memset_call (this->func_->shidden));
}
if (using_rvo_p == true)
{
/* Generate: (expr, return <retval>); */
add_stmt (build_expr_dtor (s->exp));
}
else

39
gcc/testsuite/gdc.dg/torture/pr101273.d Normal file
View File

@ -0,0 +1,39 @@
// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101273
// { dg-do run }
struct S101273
{
int x;
S101273* impl;
this(int x)
{
this.x = x;
this.impl = &this;
}
~this() { }
}
S101273 makeS101273()
{
return S101273(2);
}
S101273 nrvo101273()
{
S101273 ret = makeS101273();
return ret;
}
S101273 rvo101273()
{
return makeS101273();
}
void main()
{
auto nrvo = nrvo101273();
assert(&nrvo is nrvo.impl);
auto rvo = rvo101273();
assert(&rvo is rvo.impl);
}