[Patch SRA] Fix PR66119 by calling get_move_ratio in SRA

[James Greenhalgh <james dot greenhalgh at arm dot com>]

Hi,

The problem in PR66119 is that we assume MOVE_RATIO will be constant
for a compilation run, such that we only need to read it once at compiler
startup if we want to set up defaults for
--param sra-max-scalarization-size-Osize and
--param sra-max-scalarization-size-Osize.

This assumption is faulty. Some targets may have MOVE_RATIO set up
to use state which depends on the selected processor - which may vary
per function for a switchable target.

This patch fixes the issue by always calling get_move_ratio in the SRA
code, ensuring that an up-to-date value is used.

Unfortunately, this means we have to use 0 as a sentinel value for
the parameter - indicating no user override of the feature - and
therefore cannot use it to disable scalarization. However, there
are other ways to disable scalarazation (-fno-tree-sra) so this is not
a great loss.

Bootstrapped and tested on x86-64 and AArch64 with no issues.

OK for trunk (and 5.2 after a few days watching for fallout)?

Thanks,
James

---
gcc/

2015-06-23  James Greenhalgh  <james.greenhalgh@arm.com>

	PR tree-optimization/66119
	* doc/invoke.texi (sra-max-scalarization-size-Osize): Mention that
	"0" is used as a sentinel value.
	(sra-max-scalarization-size-Ospeed): Likewise.
	* toplev.c (process_options): Don't set up default values for
	the sra_max_scalarization_size_{speed,size} parameters.
	* tree-sra (analyze_all_variable_accesses): If no values
	have been set for the sra_max_scalarization_size_{speed,size}
	parameters, call get_move_ratio to get target defaults.

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index b99ab1c..fc9dad7 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -10894,7 +10894,9 @@ variables.  These parameters control the maximum size, in storage units,
 of aggregate which is considered for replacement when compiling for
 speed
 (@option{sra-max-scalarization-size-Ospeed}) or size
-(@option{sra-max-scalarization-size-Osize}) respectively.
+(@option{sra-max-scalarization-size-Osize}) respectively.  The
+value 0 indicates that the compiler should use an appropriate size
+for the target processor, this is the default behaviour.
 
 @item tm-max-aggregate-size
 When making copies of thread-local variables in a transaction, this
diff --git a/gcc/toplev.c b/gcc/toplev.c
index 2f43a89..902bfc7 100644
--- a/gcc/toplev.c
+++ b/gcc/toplev.c
@@ -1301,20 +1301,6 @@ process_options (void)
      so we can correctly initialize debug output.  */
   no_backend = lang_hooks.post_options (&main_input_filename);
 
-  /* Set default values for parameters relation to the Scalar Reduction
-     of Aggregates passes (SRA and IP-SRA).  We must do this here, rather
-     than in opts.c:default_options_optimization as historically these
-     tuning heuristics have been based on MOVE_RATIO, which on some
-     targets requires other symbols from the backend.  */
-  maybe_set_param_value
-    (PARAM_SRA_MAX_SCALARIZATION_SIZE_SPEED,
-     get_move_ratio (true) * UNITS_PER_WORD,
-     global_options.x_param_values, global_options_set.x_param_values);
-  maybe_set_param_value
-    (PARAM_SRA_MAX_SCALARIZATION_SIZE_SIZE,
-     get_move_ratio (false) * UNITS_PER_WORD,
-     global_options.x_param_values, global_options_set.x_param_values);
-
   /* Some machines may reject certain combinations of options.  */
   targetm.target_option.override ();
 
diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
index 8e34244..e2419af 100644
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -2549,12 +2549,24 @@ analyze_all_variable_accesses (void)
   bitmap tmp = BITMAP_ALLOC (NULL);
   bitmap_iterator bi;
   unsigned i;
+  bool optimize_speed_p = !optimize_function_for_size_p (cfun);
+
   unsigned max_scalarization_size
-    = (optimize_function_for_size_p (cfun)
-	? PARAM_VALUE (PARAM_SRA_MAX_SCALARIZATION_SIZE_SIZE)
-	: PARAM_VALUE (PARAM_SRA_MAX_SCALARIZATION_SIZE_SPEED))
+    = (optimize_speed_p
+	? PARAM_VALUE (PARAM_SRA_MAX_SCALARIZATION_SIZE_SPEED)
+	: PARAM_VALUE (PARAM_SRA_MAX_SCALARIZATION_SIZE_SIZE))
       * BITS_PER_UNIT;
 
+  /* If the user didn't set PARAM_SRA_MAX_SCALARIZATION_SIZE_<...>,
+     fall back to a target default.  This means that zero cannot be
+     used to disable scalarization as we've taken it as a sentinel
+     value.  This is not ideal, but see PR66119 for the reason we
+     can't simply set the target defaults ahead of time during option
+     handling.  */
+  if (!max_scalarization_size)
+    max_scalarization_size = get_move_ratio (optimize_speed_p)
+			     * UNITS_PER_WORD * BITS_PER_UNIT;
+
   EXECUTE_IF_SET_IN_BITMAP (candidate_bitmap, 0, i, bi)
     if (bitmap_bit_p (should_scalarize_away_bitmap, i)
 	&& !bitmap_bit_p (cannot_scalarize_away_bitmap, i))