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[patch, fortran] Fix PR 82567
- From: Thomas Koenig <tkoenig at netcologne dot de>
- To: "fortran at gcc dot gnu dot org" <fortran at gcc dot gnu dot org>, gcc-patches <gcc-patches at gcc dot gnu dot org>
- Date: Wed, 18 Oct 2017 00:36:34 +0200
- Subject: [patch, fortran] Fix PR 82567
- Authentication-results: sourceware.org; auth=none
Hello world,
this patch fixes a regression with long compile times,
which came about due to our handling of array constructors
at compile time. This, togeteher with a simplification in
front end optimization, led to long compile times and large
code.
Regression-tested. OK for trunk and the other affected branches?
Regards
Thomas
2917-10-17 Thomas Koenig <tkoenig@gcc.gnu.org>
PR fortran/82567
* frontend-passes.c (combine_array_constructor): If an array
constructor is all constants and has more elements than a small
constant, don't convert a*[b,c] to [a*b,a*c] to reduce compilation
times.
2917-10-17 Thomas Koenig <tkoenig@gcc.gnu.org>
PR fortran/82567
* gfortran.dg/array_constructor_51.f90: New test.
! { dg-do compile }
! { dg-additional-options "-ffrontend-optimize -fdump-tree-original" }
! PR 82567 - long compile times caused by large constant constructors
! multiplied by variables
SUBROUTINE sub()
IMPLICIT NONE
INTEGER, PARAMETER :: n = 1000
REAL, ALLOCATABLE :: x(:)
REAL :: xc, h
INTEGER :: i
ALLOCATE( x(n) )
xc = 100.
h = xc/n
x = h*[(i,i=1,n)]
end
! { dg-final { scan-tree-dump-times "__var" 0 "original" } }
Index: frontend-passes.c
===================================================================
--- frontend-passes.c (Revision 253768)
+++ frontend-passes.c (Arbeitskopie)
@@ -1635,6 +1635,8 @@ combine_array_constructor (gfc_expr *e)
gfc_constructor *c, *new_c;
gfc_constructor_base oldbase, newbase;
bool scalar_first;
+ int n_elem;
+ bool all_const;
/* Array constructors have rank one. */
if (e->rank != 1)
@@ -1674,12 +1676,38 @@ combine_array_constructor (gfc_expr *e)
if (op2->ts.type == BT_CHARACTER)
return false;
- scalar = create_var (gfc_copy_expr (op2), "constr");
+ /* This might be an expanded constructor with very many constant values. If
+ we perform the operation here, we might end up with a long compile time,
+ so an arbitrary length bound is in order here. If the constructor
+ constains something which is not a constant, it did not come from an
+ expansion, so leave it alone. */
+#define CONSTR_LEN_MAX 42
+
oldbase = op1->value.constructor;
+
+ n_elem = 0;
+ all_const = true;
+ for (c = gfc_constructor_first (oldbase); c; c = gfc_constructor_next(c))
+ {
+ if (c->expr->expr_type != EXPR_CONSTANT)
+ {
+ all_const = false;
+ break;
+ }
+ n_elem += 1;
+ }
+
+ if (all_const && n_elem > CONSTR_LEN_MAX)
+ return false;
+
+#undef CONSTR_LEN_MAX
+
newbase = NULL;
e->expr_type = EXPR_ARRAY;
+ scalar = create_var (gfc_copy_expr (op2), "constr");
+
for (c = gfc_constructor_first (oldbase); c;
c = gfc_constructor_next (c))
{