[Patch, Fortran] Use ANNOTATE_EXPR annot_expr_ivdep_kind for DO CONCURRENT

[Tobias Burnus <burnus at net-b dot de>]

This patch requires my pending ME and C FE patch: 
http://gcc.gnu.org/ml/gcc-patches/2013-10/msg00514.html

Using C/C++'s #pragma ivdep or â with the attached Fortran patch â "do 
concurrent", the loop condition is annotated such that later the loop's 
vectorization safelen is set to infinity (well, INT_MAX). The main 
purpose is to tell the compiler that the result is independent of the 
order in which the loop is walked. The typical case is pointer aliasing, 
in which the compiler either doesn't vectorize or adds a run-time 
aliasing check (loop versioning). With the annotation, the compiler 
simply assumes that there is no aliasing and avoids the versioning. â 
Contrary to C++ which does not even have the "restrict" qualifier (gcc 
and others do support __restrict) and cases where C/C++'s __restrict 
qualifier isn't sufficient/applicable, the effect on typical Fortran 
code should be smaller as most variables cannot alias. Still, in some 
cases it can help. (See test case for an example.)

There is an alternative to ivdep, which is more lower level [1]: 
OpenMPv4's "omp simd" (with safelen=) for C/C++/Fortran and â for C/C++ 
â Cilk Plus's #pragma simd.

Build and regtested on x86-64-gnu-linux.
OK for the trunk?

Tobias

PS: I think the same annotation could be also used with FORALL and 
implied loops with whole-array/array-section assignments, when the FE 
knows that there is no aliasing between the LHS and RHS side. (In some 
cases, the FE knows this while the ME doesn't.)

PPS: My personal motivation is my long-standing wish to pass this 
information to the middle end for DO CONCURRENT but also to use the 
pragma for a specific C++ code.

[1] The OpenMPv4 support for C/C++ will be merged soon, for Fortran it 
will take a while (maybe still in 4.9, maybe only later). See 
http://gcc.gnu.org/ml/gcc-patches/2013-10/msg00502.html / The relevant 
Cilk Plus patch has been posted at 
http://gcc.gnu.org/ml/gcc-patches/2013-08/msg01626.html
2013-10-08  Tobias Burnus  <burnus@net-b.de>

	PR fortran/44646
	* trans-stmt.c (struct forall_info): Add do_concurrent field.
	(gfc_trans_forall_1): Set it for do concurrent.
	(gfc_trans_forall_loop): Mark those as annot_expr_ivdep_kind.

2013-10-08  Tobias Burnus  <burnus@net-b.de>

	PR fortran/44646
	* gfortran.dg/vect/vect-do-concurrent-1.f90: New.

diff --git a/gcc/fortran/trans-stmt.c b/gcc/fortran/trans-stmt.c
index edd2dac..b44d2c1 100644
--- a/gcc/fortran/trans-stmt.c
+++ b/gcc/fortran/trans-stmt.c
@@ -53,6 +53,7 @@ typedef struct forall_info
   int nvar;
   tree size;
   struct forall_info  *prev_nest;
+  bool do_concurrent;
 }
 forall_info;
 
@@ -2759,6 +2760,12 @@ gfc_trans_forall_loop (forall_info *forall_tmp, tree body,
       /* The exit condition.  */
       cond = fold_build2_loc (input_location, LE_EXPR, boolean_type_node,
 			      count, build_int_cst (TREE_TYPE (count), 0));
+      if (forall_tmp->do_concurrent)
+	{
+	  cond = build1 (ANNOTATE_EXPR, TREE_TYPE (cond), cond);
+	  SET_ANNOTATE_EXPR_ID (cond, annot_expr_ivdep_kind);
+	}
+
       tmp = build1_v (GOTO_EXPR, exit_label);
       tmp = fold_build3_loc (input_location, COND_EXPR, void_type_node,
 			     cond, tmp, build_empty_stmt (input_location));
@@ -3842,6 +3849,7 @@ gfc_trans_forall_1 (gfc_code * code, forall_info * nested_forall_info)
 	}
 
       tmp = gfc_finish_block (&body);
+      nested_forall_info->do_concurrent = true;
       tmp = gfc_trans_nested_forall_loop (nested_forall_info, tmp, 1);
       gfc_add_expr_to_block (&block, tmp);
       goto done;
diff --git a/gcc/testsuite/gfortran.dg/vect/vect-do-concurrent-1.f90 b/gcc/testsuite/gfortran.dg/vect/vect-do-concurrent-1.f90
new file mode 100644
index 0000000..7d56241
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/vect/vect-do-concurrent-1.f90
@@ -0,0 +1,17 @@
+! { dg-do compile }
+! { dg-require-effective-target vect_float }
+! { dg-options "-O3 -fopt-info-vec-optimized" }
+
+subroutine test(n, a, b, c)
+  integer, value :: n
+  real, contiguous,  pointer :: a(:), b(:), c(:)
+  integer :: i
+  do concurrent (i = 1:n)
+    a(i) = b(i) + c(i)
+  end do
+end subroutine test
+
+! { dg-message "loop vectorized" "" { target *-*-* } 0 }
+! { dg-bogus "version" "" { target *-*-* } 0 }
+! { dg-bogus "alias" "" { target *-*-* } 0 }
+! { dg-final { cleanup-tree-dump "vect" } }