Make targetm.get_mask_mode return an opt_mode

...for consistency with mode_for_vector.

2017-09-05  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* target.def (get_mask_mode): Change return type to opt_mode.
	Expand commentary.
	* doc/tm.texi: Regenerate.
	* targhooks.h (default_get_mask_mode): Return an opt_mode.
	* targhooks.c (default_get_mask_mode): Likewise.
	* config/i386/i386.c (ix86_get_mask_mode): Likewise.
	* optabs-query.c (can_vec_mask_load_store_p): Update use of
	targetm.get_mask_mode.
	* tree.c (build_truth_vector_type): Likewise.

From-SVN: r251731

8 files changed, 50 insertions, 33 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 067040b..f521a27 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,17 @@
 2017-09-05  Richard Sandiford  <richard.sandiford@linaro.org>
 
+	* target.def (get_mask_mode): Change return type to opt_mode.
+	Expand commentary.
+	* doc/tm.texi: Regenerate.
+	* targhooks.h (default_get_mask_mode): Return an opt_mode.
+	* targhooks.c (default_get_mask_mode): Likewise.
+	* config/i386/i386.c (ix86_get_mask_mode): Likewise.
+	* optabs-query.c (can_vec_mask_load_store_p): Update use of
+	targetm.get_mask_mode.
+	* tree.c (build_truth_vector_type): Likewise.
+
+2017-09-05  Richard Sandiford  <richard.sandiford@linaro.org>
+
 	* machmode.h (mode_for_vector): Return an opt_mode.
 	* stor-layout.c (mode_for_vector): Likewise.
 	(mode_for_int_vector): Update accordingly.
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 8c17da2..4e93cc1 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -51714,7 +51714,7 @@ ix86_autovectorize_vector_sizes (void)
 
 /* Implemenation of targetm.vectorize.get_mask_mode.  */
 
-static machine_mode
+static opt_machine_mode
 ix86_get_mask_mode (unsigned nunits, unsigned vector_size)
 {
   unsigned elem_size = vector_size / nunits;
@@ -51732,7 +51732,7 @@ ix86_get_mask_mode (unsigned nunits, unsigned vector_size)
 
   gcc_assert (elem_size * nunits == vector_size);
 
-  return mode_for_vector (elem_mode, nunits).else_blk ();
+  return mode_for_vector (elem_mode, nunits);
 }
 
 
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 2e22047..c29d249 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -5820,10 +5820,16 @@ mode returned by @code{TARGET_VECTORIZE_PREFERRED_SIMD_MODE}.
 The default is zero which means to not iterate over other vector sizes.
 @end deftypefn
 
-@deftypefn {Target Hook} machine_mode TARGET_VECTORIZE_GET_MASK_MODE (unsigned @var{nunits}, unsigned @var{length})
-This hook returns mode to be used for a mask to be used for a vector
-of specified @var{length} with @var{nunits} elements.  By default an integer
-vector mode of a proper size is returned.
+@deftypefn {Target Hook} opt_machine_mode TARGET_VECTORIZE_GET_MASK_MODE (unsigned @var{nunits}, unsigned @var{length})
+A vector mask is a value that holds one boolean result for every element
+in a vector.  This hook returns the machine mode that should be used to
+represent such a mask when the vector in question is @var{length} bytes
+long and contains @var{nunits} elements.  The hook returns an empty
+@code{opt_machine_mode} if no such mode exists.
+
+The default implementation returns the mode of an integer vector that
+is @var{length} bytes long and that contains @var{nunits} elements,
+if such a mode exists.
 @end deftypefn
 
 @deftypefn {Target Hook} {void *} TARGET_VECTORIZE_INIT_COST (struct loop *@var{loop_info})
diff --git a/gcc/optabs-query.c b/gcc/optabs-query.c
index 9afdd1f..81b1bd9 100644
--- a/gcc/optabs-query.c
+++ b/gcc/optabs-query.c
@@ -531,12 +531,9 @@ can_vec_mask_load_store_p (machine_mode mode,
   if (!VECTOR_MODE_P (vmode))
     return false;
 
-  mask_mode = targetm.vectorize.get_mask_mode (GET_MODE_NUNITS (vmode),
-					       GET_MODE_SIZE (vmode));
-  if (mask_mode == VOIDmode)
-    return false;
-
-  if (convert_optab_handler (op, vmode, mask_mode) != CODE_FOR_nothing)
+  if ((targetm.vectorize.get_mask_mode
+       (GET_MODE_NUNITS (vmode), GET_MODE_SIZE (vmode)).exists (&mask_mode))
+      && convert_optab_handler (op, vmode, mask_mode) != CODE_FOR_nothing)
     return true;
 
   vector_sizes = targetm.vectorize.autovectorize_vector_sizes ();
@@ -548,12 +545,10 @@ can_vec_mask_load_store_p (machine_mode mode,
 	continue;
       unsigned int nunits = cur / GET_MODE_SIZE (smode);
       if (mode_for_vector (smode, nunits).exists (&vmode)
-	  && VECTOR_MODE_P (vmode))
-	{
-	  mask_mode = targetm.vectorize.get_mask_mode (nunits, cur);
-	  if (convert_optab_handler (op, vmode, mask_mode) != CODE_FOR_nothing)
-	    return true;
-	}
+	  && VECTOR_MODE_P (vmode)
+	  && targetm.vectorize.get_mask_mode (nunits, cur).exists (&mask_mode)
+	  && convert_optab_handler (op, vmode, mask_mode) != CODE_FOR_nothing)
+	return true;
     }
   return false;
 }
diff --git a/gcc/target.def b/gcc/target.def
index a9417578..110300c 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -1877,10 +1877,16 @@ The default is zero which means to not iterate over other vector sizes.",
 /* Function to get a target mode for a vector mask.  */
 DEFHOOK
 (get_mask_mode,
- "This hook returns mode to be used for a mask to be used for a vector\n\
-of specified @var{length} with @var{nunits} elements.  By default an integer\n\
-vector mode of a proper size is returned.",
- machine_mode,
+ "A vector mask is a value that holds one boolean result for every element\n\
+in a vector.  This hook returns the machine mode that should be used to\n\
+represent such a mask when the vector in question is @var{length} bytes\n\
+long and contains @var{nunits} elements.  The hook returns an empty\n\
+@code{opt_machine_mode} if no such mode exists.\n\
+\n\
+The default implementation returns the mode of an integer vector that\n\
+is @var{length} bytes long and that contains @var{nunits} elements,\n\
+if such a mode exists.",
+ opt_machine_mode,
  (unsigned nunits, unsigned length),
  default_get_mask_mode)
 
diff --git a/gcc/targhooks.c b/gcc/targhooks.c
index 078647c..cbc15ab 100644
--- a/gcc/targhooks.c
+++ b/gcc/targhooks.c
@@ -1200,7 +1200,7 @@ default_autovectorize_vector_sizes (void)
 
 /* By defaults a vector of integers is used as a mask.  */
 
-machine_mode
+opt_machine_mode
 default_get_mask_mode (unsigned nunits, unsigned vector_size)
 {
   unsigned elem_size = vector_size / nunits;
@@ -1210,12 +1210,12 @@ default_get_mask_mode (unsigned nunits, unsigned vector_size)
 
   gcc_assert (elem_size * nunits == vector_size);
 
-  if (!mode_for_vector (elem_mode, nunits).exists (&vector_mode)
-      || !VECTOR_MODE_P (vector_mode)
-      || !targetm.vector_mode_supported_p (vector_mode))
-    vector_mode = BLKmode;
+  if (mode_for_vector (elem_mode, nunits).exists (&vector_mode)
+      && VECTOR_MODE_P (vector_mode)
+      && targetm.vector_mode_supported_p (vector_mode))
+    return vector_mode;
 
-  return vector_mode;
+  return opt_machine_mode ();
 }
 
 /* By default, the cost model accumulates three separate costs (prologue,
diff --git a/gcc/targhooks.h b/gcc/targhooks.h
index a7fb83a2..5178086 100644
--- a/gcc/targhooks.h
+++ b/gcc/targhooks.h
@@ -102,7 +102,7 @@ default_builtin_support_vector_misalignment (machine_mode mode,
 					     int, bool);
 extern machine_mode default_preferred_simd_mode (scalar_mode mode);
 extern unsigned int default_autovectorize_vector_sizes (void);
-extern machine_mode default_get_mask_mode (unsigned, unsigned);
+extern opt_machine_mode default_get_mask_mode (unsigned, unsigned);
 extern void *default_init_cost (struct loop *);
 extern unsigned default_add_stmt_cost (void *, int, enum vect_cost_for_stmt,
 				       struct _stmt_vec_info *, int,
diff --git a/gcc/tree.c b/gcc/tree.c
index 0420808..7a70eb7 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -10243,10 +10243,8 @@ build_vector_type (tree innertype, int nunits)
 tree
 build_truth_vector_type (unsigned nunits, unsigned vector_size)
 {
-  machine_mode mask_mode = targetm.vectorize.get_mask_mode (nunits,
-							    vector_size);
-
-  gcc_assert (mask_mode != VOIDmode);
+  machine_mode mask_mode
+    = targetm.vectorize.get_mask_mode (nunits, vector_size).else_blk ();
 
   unsigned HOST_WIDE_INT vsize;
   if (mask_mode == BLKmode)