This fixes PR49957 by keeping the array index into a multi-dimensional array in optimal associated form which is ((off + outermost) + ...) + innermost) + constant) so that dependence analysis can properly handle it. It doesn't work right now because we build the expression in reverse order, fold thinks it can do some fancy and the expression is of signed type and thus we know it doesn't overflow but we also won't re-associate it to a more optimal form.
I tried reversing the loop in gfc_conv_array_ref but that doesn't work (for example aliasing_dummy_4.f90 ICEs), thus the funny way of chaining the pluses. I also don't know if there is maybe another place we build similar expressions that should be adjusted, too - this one is where we build the expression for the testcase I looked at. The patch doesn't make 410.bwaves measurably faster, but at least it also doesn't get slower. Bootstrap and regtest is currently running on x86_64-unknown-linux-gnu, the reversed loop one was ok (well, apart from those 2-3 fails). Comments? Any idea why reversing the loop would break? The ICE I got is /space/rguenther/src/svn/trunk/gcc/testsuite/gfortran.dg/aliasing_dummy_4.f90: In function 'test_f90': /space/rguenther/src/svn/trunk/gcc/testsuite/gfortran.dg/aliasing_dummy_4.f90:21:0: internal compiler error: in gfc_conv_constant, at fortran/trans-const.c:387 Please submit a full bug report, with preprocessed source if appropriate. See <http://gcc.gnu.org/bugs.html> for instructions. Thanks, Richard. 2011-08-03 Richard Guenther <rguent...@suse.de> PR fortran/49957 * trans-array.c (gfc_conv_array_ref): Build the array index expression in optimally associated order. * gfortran.dg/vect/O3-pr49957.f: New testcase. Index: gcc/fortran/trans-array.c =================================================================== --- gcc/fortran/trans-array.c (revision 177094) +++ gcc/fortran/trans-array.c (working copy) @@ -2634,7 +2634,7 @@ gfc_conv_array_ref (gfc_se * se, gfc_arr locus * where) { int n; - tree index; + tree index, offset, *indexp; tree tmp; tree stride; gfc_se indexse; @@ -2669,9 +2669,16 @@ gfc_conv_array_ref (gfc_se * se, gfc_arr return; } - index = gfc_index_zero_node; + offset = gfc_conv_array_offset (se->expr); + if (TREE_CODE (offset) != INTEGER_CST) + index = offset; + else + index = gfc_index_zero_node; - /* Calculate the offsets from all the dimensions. */ + indexp = &index; + + /* Calculate the offsets from all the dimensions. Make sure to associate + the final offset so that we form a chain of loop invariant summands. */ for (n = 0; n < ar->dimen; n++) { /* Calculate the index for this dimension. */ @@ -2740,15 +2747,38 @@ gfc_conv_array_ref (gfc_se * se, gfc_arr tmp = fold_build2_loc (input_location, MULT_EXPR, gfc_array_index_type, indexse.expr, stride); - /* And add it to the total. */ - index = fold_build2_loc (input_location, PLUS_EXPR, - gfc_array_index_type, index, tmp); + /* And add it to the total. Avoid folding as that re-associates + in a non-optimal way. We want to have constant offsets as + the outermost addition and the rest of the additions in order + of the loop depth. */ + if (!integer_zerop (index)) + { + if (TREE_CODE (tmp) == INTEGER_CST) + { + bool reset = indexp == &index; + index = fold_build2_loc (input_location, PLUS_EXPR, + gfc_array_index_type, index, tmp); + if (reset) + indexp = &index; + } + else + { + *indexp + = build2_loc (input_location, PLUS_EXPR, + gfc_array_index_type, *indexp, tmp); + indexp = &TREE_OPERAND (*indexp, 0); + } + } + else + { + index = tmp; + indexp = &index; + } } - tmp = gfc_conv_array_offset (se->expr); - if (!integer_zerop (tmp)) + if (TREE_CODE (offset) == INTEGER_CST) index = fold_build2_loc (input_location, PLUS_EXPR, - gfc_array_index_type, index, tmp); + gfc_array_index_type, index, offset); /* Access the calculated element. */ tmp = gfc_conv_array_data (se->expr); Index: gcc/testsuite/gfortran.dg/vect/O3-pr49957.f =================================================================== --- gcc/testsuite/gfortran.dg/vect/O3-pr49957.f (revision 0) +++ gcc/testsuite/gfortran.dg/vect/O3-pr49957.f (revision 0) @@ -0,0 +1,16 @@ +! { dg-do compile } +! { dg-require-effective-target vect_double } + subroutine shell(nx,ny,nz) + implicit none + integer i,j,k,l,nx,ny,nz + real*8 q(5,nx,ny),dq(5,nx,ny) + do j=1,ny + do i=1,nx + do l=1,5 + q(l,i,j)=q(l,i,j)+dq(l,i,j) + enddo + enddo + enddo + return + end +! { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail vect_no_align } } }
