ira: Add a target hook for callee-saved register cost scale

commit 3b9b8d6cfd
Author: Surya Kumari Jangala <jskumari@linux.ibm.com>
Date:   Tue Jun 25 08:37:49 2024 -0500

    ira: Scale save/restore costs of callee save registers with block frequency

scales the cost of saving/restoring a callee-save hard register in epilogue
and prologue with the entry block frequency, which, if not optimizing for
size, is 10000, for all targets.  As the result, callee-saved registers
may not be used to preserve local variable values across calls on some
targets, like x86.  Add a target hook for the callee-saved register cost
scale in epilogue and prologue used by IRA.  The default version of this
target hook returns 1 if optimizing for size, otherwise returns the entry
block frequency.  Add an x86 version of this target hook to restore the
old behavior prior to the above commit.

	PR rtl-optimization/111673
	PR rtl-optimization/115932
	PR rtl-optimization/116028
	PR rtl-optimization/117081
	PR rtl-optimization/117082
	PR rtl-optimization/118497
	* ira-color.cc (assign_hard_reg): Call the target hook for the
	callee-saved register cost scale in epilogue and prologue.
	* target.def (ira_callee_saved_register_cost_scale): New target
	hook.
	* targhooks.cc (default_ira_callee_saved_register_cost_scale):
	New.
	* targhooks.h (default_ira_callee_saved_register_cost_scale):
	Likewise.
	* config/i386/i386.cc (ix86_ira_callee_saved_register_cost_scale):
	New.
	(TARGET_IRA_CALLEE_SAVED_REGISTER_COST_SCALE): Likewise.
	* doc/tm.texi: Regenerated.
	* doc/tm.texi.in (TARGET_IRA_CALLEE_SAVED_REGISTER_COST_SCALE):
	New.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>

gcc/config/i386/i386.cc

@@ -20600,6 +20600,14 @@ ix86_class_likely_spilled_p (reg_class_t rclass)
   return false;
 }
 
+/* Implement TARGET_IRA_CALLEE_SAVED_REGISTER_COST_SCALE.  */
+
+static int
+ix86_ira_callee_saved_register_cost_scale (int)
+{
+  return 1;
+}
+
 /* Return true if a set of DST by the expression SRC should be allowed.
    This prevents complex sets of likely_spilled hard regs before split1.  */
 
@@ -27078,6 +27086,9 @@ ix86_libgcc_floating_mode_supported_p
 #define TARGET_PREFERRED_OUTPUT_RELOAD_CLASS ix86_preferred_output_reload_class
 #undef TARGET_CLASS_LIKELY_SPILLED_P
 #define TARGET_CLASS_LIKELY_SPILLED_P ix86_class_likely_spilled_p
+#undef TARGET_IRA_CALLEE_SAVED_REGISTER_COST_SCALE
+#define TARGET_IRA_CALLEE_SAVED_REGISTER_COST_SCALE \
+  ix86_ira_callee_saved_register_cost_scale
 
 #undef TARGET_VECTORIZE_BUILTIN_VECTORIZATION_COST
 #define TARGET_VECTORIZE_BUILTIN_VECTORIZATION_COST \

gcc/doc/tm.texi

@@ -3047,6 +3047,14 @@ A target hook which can change allocno class for given pseudo from
   The default version of this target hook always returns given class.
 @end deftypefn
 
+@deftypefn {Target Hook} int TARGET_IRA_CALLEE_SAVED_REGISTER_COST_SCALE (int @var{hard_regno})
+A target hook which returns the callee-saved register @var{hard_regno}
+cost scale in epilogue and prologue used by IRA.
+
+The default version of this target hook returns 1 if optimizing for
+size, otherwise returns the entry block frequency.
+@end deftypefn
+
 @deftypefn {Target Hook} bool TARGET_LRA_P (void)
 A target hook which returns true if we use LRA instead of reload pass.
 

gcc/doc/tm.texi.in

@@ -2388,6 +2388,8 @@ in the reload pass.
 
 @hook TARGET_IRA_CHANGE_PSEUDO_ALLOCNO_CLASS
 
+@hook TARGET_IRA_CALLEE_SAVED_REGISTER_COST_SCALE
+
 @hook TARGET_LRA_P
 
 @hook TARGET_REGISTER_PRIORITY

gcc/ira-color.cc

@@ -2180,8 +2180,7 @@ assign_hard_reg (ira_allocno_t a, bool retry_p)
 		         + ira_memory_move_cost[mode][rclass][1])
 		        * saved_nregs / hard_regno_nregs (hard_regno,
 							  mode) - 1)
-		       * (optimize_size ? 1 :
-			  REG_FREQ_FROM_BB (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
+		       * targetm.ira_callee_saved_register_cost_scale (hard_regno);
 	    cost += add_cost;
 	    full_cost += add_cost;
 	  }

gcc/target.def

@@ -5714,6 +5714,18 @@ DEFHOOK
  reg_class_t, (int, reg_class_t, reg_class_t),
  default_ira_change_pseudo_allocno_class)
 
+/* Scale of callee-saved register cost in epilogue and prologue used by
+   IRA.  */
+DEFHOOK
+(ira_callee_saved_register_cost_scale,
+ "A target hook which returns the callee-saved register @var{hard_regno}\n\
+cost scale in epilogue and prologue used by IRA.\n\
+\n\
+The default version of this target hook returns 1 if optimizing for\n\
+size, otherwise returns the entry block frequency.",
+ int, (int hard_regno),
+ default_ira_callee_saved_register_cost_scale)
+
 /* Return true if we use LRA instead of reload.  */
 DEFHOOK
 (lra_p,

gcc/targhooks.cc

@@ -1305,6 +1305,14 @@ default_ira_change_pseudo_allocno_class (int regno ATTRIBUTE_UNUSED,
   return cl;
 }
 
+int
+default_ira_callee_saved_register_cost_scale (int)
+{
+  return (optimize_size
+	  ? 1
+	  : REG_FREQ_FROM_BB (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
+}
+
 extern bool
 default_lra_p (void)
 {

gcc/targhooks.h

@@ -173,6 +173,7 @@ extern void default_emit_call_builtin___clear_cache (rtx, rtx);
 extern poly_int64 default_return_pops_args (tree, tree, poly_int64);
 extern reg_class_t default_ira_change_pseudo_allocno_class (int, reg_class_t,
 							    reg_class_t);
+extern int default_ira_callee_saved_register_cost_scale (int);
 extern bool default_lra_p (void);
 extern int default_register_priority (int);
 extern bool default_register_usage_leveling_p (void);