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 <tkoe...@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 <tkoe...@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)) {