Add a vect_variable_length target selector

This patch adds a target selector for variable-length vectors.
Initially it's always false, but the SVE patch provides a case
in which it's true.

2017-11-09  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* doc/sourcebuild.texi (vect_variable_length): Document.

gcc/testsuite/
	* lib/target-supports.exp
	(check_effective_target_vect_variable_length): New proc.
	* gcc.dg/vect/pr60482.c: XFAIL test for no epilog loop if
	vect_variable_length.
	* gcc.dg/vect/slp-reduc-6.c: XFAIL two-operation SLP if
	vect_variable_length.
	* gcc.dg/vect/vect-alias-check-5.c: XFAIL alias optimization if
	vect_variable_length.
	* gfortran.dg/vect/fast-math-mgrid-resid.f: XFAIL predictive
	commoning optimization if vect_variable_length.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r254595

gcc/ChangeLog

@@ -2,6 +2,12 @@
 	    Alan Hayward  <alan.hayward@arm.com>
 	    David Sherwood  <david.sherwood@arm.com>
 
+	* doc/sourcebuild.texi (vect_variable_length): Document.
+
+2017-11-09  Richard Sandiford  <richard.sandiford@linaro.org>
+	    Alan Hayward  <alan.hayward@arm.com>
+	    David Sherwood  <david.sherwood@arm.com>
+
 	* doc/sourcebuild.texi (vect_unaligned_possible): Document.
 
 2017-11-09  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/doc/sourcebuild.texi

@@ -1486,6 +1486,9 @@ Target prefers vectors to have an alignment greater than element
 alignment, but also allows unaligned vector accesses in some
 circumstances.
 
+@item vect_variable_length
+Target has variable-length vectors.
+
 @item vect_widen_sum_hi_to_si
 Target supports a vector widening summation of @code{short} operands
 into @code{int} results, or can promote (unpack) from @code{short}

gcc/testsuite/ChangeLog

@@ -3,6 +3,21 @@
 	    David Sherwood  <david.sherwood@arm.com>
 
 	* lib/target-supports.exp
+	(check_effective_target_vect_variable_length): New proc.
+	* gcc.dg/vect/pr60482.c: XFAIL test for no epilog loop if
+	vect_variable_length.
+	* gcc.dg/vect/slp-reduc-6.c: XFAIL two-operation SLP if
+	vect_variable_length.
+	* gcc.dg/vect/vect-alias-check-5.c: XFAIL alias optimization if
+	vect_variable_length.
+	* gfortran.dg/vect/fast-math-mgrid-resid.f: XFAIL predictive
+	commoning optimization if vect_variable_length.
+
+2017-11-09  Richard Sandiford  <richard.sandiford@linaro.org>
+	    Alan Hayward  <alan.hayward@arm.com>
+	    David Sherwood  <david.sherwood@arm.com>
+
+	* lib/target-supports.exp
 	(check_effective_target_vect_unaligned_possible): New proc.
 	* gcc.dg/vect/slp-25.c: Extend XFAIL of peeling for alignment from
 	vect_no_align && { ! vect_hw_misalign } to ! vect_unaligned_possible.

gcc/testsuite/gcc.dg/vect/pr60482.c

@@ -16,4 +16,6 @@ foo (double *x, int n)
   return p;
 }
 
-/* { dg-final { scan-tree-dump-not "epilog loop required" "vect" } } */
+/* Until fully-masked loops are supported, we always need an epilog
+   loop for variable-length vectors.  */
+/* { dg-final { scan-tree-dump-not "epilog loop required" "vect" { xfail vect_variable_length } } } */

gcc/testsuite/gcc.dg/vect/slp-reduc-6.c

@@ -44,5 +44,5 @@ int main (void)
 
 /* { dg-final { scan-tree-dump-times "vectorized 1 loops" 2 "vect" { xfail { vect_no_int_add || { ! { vect_unpack || vect_strided2 } } } } } } */
 /* { dg-final { scan-tree-dump-times "vectorizing stmts using SLP" 0 "vect" } } */
-/* { dg-final { scan-tree-dump-times "different interleaving chains in one node" 1 "vect" { target { ! vect_no_int_add } } } } */
+/* { dg-final { scan-tree-dump-times "different interleaving chains in one node" 1 "vect" { target { ! vect_no_int_add } xfail vect_variable_length } } } */
 

gcc/testsuite/gcc.dg/vect/vect-alias-check-5.c

@@ -15,5 +15,5 @@ f1 (struct s *a, struct s *b)
 }
 
 /* { dg-final { scan-tree-dump-times "consider run-time aliasing" 1 "vect" } } */
-/* { dg-final { scan-tree-dump-times "improved number of alias checks from 1 to 0" 1 "vect" } } */
+/* { dg-final { scan-tree-dump-times "improved number of alias checks from 1 to 0" 1 "vect" { xfail vect_variable_length } } } */
 /* { dg-final { scan-tree-dump-times "LOOP VECTORIZED" 1 "vect" } } */

gcc/testsuite/gfortran.dg/vect/fast-math-mgrid-resid.f

@@ -42,5 +42,5 @@ C
 ! vectorized loop.  If vector factor is 2, the vectorized loop can
 ! be predictive commoned, we check if predictive commoning PHI node
 ! is created with vector(2) type.
-! { dg-final { scan-tree-dump "Executing predictive commoning without unrolling" "pcom" } }
-! { dg-final { scan-tree-dump "vectp_u.*__lsm.* = PHI <.*vectp_u.*__lsm" "pcom" } }
+! { dg-final { scan-tree-dump "Executing predictive commoning without unrolling" "pcom" { xfail vect_variable_length } } }
+! { dg-final { scan-tree-dump "vectp_u.*__lsm.* = PHI <.*vectp_u.*__lsm" "pcom" { xfail vect_variable_length } } }

gcc/testsuite/lib/target-supports.exp

@@ -6714,6 +6714,12 @@ proc check_effective_target_vect_multiple_sizes { } {
     return [expr { [llength [available_vector_sizes]] > 1 }]
 }
 
+# Return true if variable-length vectors are supported.
+
+proc check_effective_target_vect_variable_length { } {
+    return [expr { [lindex [available_vector_sizes] 0] == 0 }]
+}
+
 # Return 1 if the target supports vectors of 64 bits.
 
 proc check_effective_target_vect64 { } {