Remove call_fixed_reg_set

On targets that use reload, call_fixed_reg_set is structurally:

  fixed_reg_set                           -- reginfo.c
  | (call_used_reg_set & ~have_save_mode) -- first loop in init_caller_save
  | ~have_save_insn                       -- final loop in init_caller_save

(where "have_save_mode" and "have_save_insn" are just my names).
But the final loop in init_caller_save does:

  for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
    for (j = 1; j <= MOVE_MAX_WORDS; j++)
      if (reg_save_code (i,regno_save_mode[i][j]) == -1)

This last condition ought to be true whenever:

  regno_save_mode[i][j] == VOIDmode

since either targetm.hard_regno_mode_ok (i, VOIDmode) should be
false or the VOIDmode save & restore shouldn't match any move insn.
And after the first loop, regno_save_mode[i][j] == VOIDmode whenever
!call_used_regs[i].  So the above is actually:

  fixed_reg_set
  | (call_used_reg_set & ~have_save_mode)
  | (~call_used_reg_set | ~have_save_insn)

which simplifies to:

  fixed_reg_set                        -- reginfo.c
  | ~have_save_mode                    -- first loop in init_caller_save
  | ~have_save_insn                    -- final loop in init_caller_save
  | ~call_used_reg_set                 -- final loop in init_caller_save

So:

  ~call_fixed_reg_set == (~fixed_reg_set
		          & have_save_mode
			  & have_save_insn
			  & call_used_reg_set)  [A]

All users have the form:

  (call_used_reg_set or some subset) & ~(call_fixed_reg_set | ...)

i.e.:

  (call_used_reg_set or some subset) & ~call_fixed_reg_set & ~(...)

We can therefore drop the "& call_used_reg_set" from [A], leaving:

  ~fixed_reg_set & have_save_mode & have_save_insn

This patch combines have_save_mode & have_save_insn into a single
condition "a save is possible", represented as savable_regs.
We can then substitute:

  ~call_fixed_reg_set --> ~fixed_reg_set & savable_regs
                          (registers we can actually save around calls)

The patch also sets regno_save_mode[i][j] for all registers,
in case non-default ABIs require a save when the default ABI
doesn't.  This ensures that savable_regs (like fixed_reg_set but
unlike call_fixed_reg_set) isn't affected by the ABI.  This only
becomes significant with later patches and at this point is just
a simplification.

Since init_caller_save is only called for reload targets,
the default assumption for LRA is that all registers are savable,
just like the default assumption before the patch was that
(~)call_fixed_reg_set == (~)fixed_reg_set.

2019-09-10  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* hard-reg-set.h (target_hard_regs::x_call_fixed_reg_set): Delete.
	(target_hard_regs::x_savable_regs): New field.
	(call_fixed_reg_set): Delete.
	(savable_regs): New macro,
	* reginfo.c (globalize_reg): Don't set call_fixed_reg_set.
	(init_reg_sets_1): Likewise.  Initialize savable_regs.
	* caller-save.c (init_caller_save): Invoke HARD_REGNO_CALLER_SAVE_MODE
	for all registers.  Set savable_regs instead of call_fixed_reg_set.
	(setup_save_areas, save_call_clobbered_regs): Replace uses of
	~call_fixed_reg_set with ~fixed_reg_set & savable_regs.
	* config/sh/sh.c (output_stack_adjust): Likewise.

From-SVN: r275598

gcc/ChangeLog

@@ -1,3 +1,17 @@
+2019-09-10  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* hard-reg-set.h (target_hard_regs::x_call_fixed_reg_set): Delete.
+	(target_hard_regs::x_savable_regs): New field.
+	(call_fixed_reg_set): Delete.
+	(savable_regs): New macro,
+	* reginfo.c (globalize_reg): Don't set call_fixed_reg_set.
+	(init_reg_sets_1): Likewise.  Initialize savable_regs.
+	* caller-save.c (init_caller_save): Invoke HARD_REGNO_CALLER_SAVE_MODE
+	for all registers.  Set savable_regs instead of call_fixed_reg_set.
+	(setup_save_areas, save_call_clobbered_regs): Replace uses of
+	~call_fixed_reg_set with ~fixed_reg_set & savable_regs.
+	* config/sh/sh.c (output_stack_adjust): Likewise.
+
 2019-09-10  Richard Sandiford  <richard.sandiford@arm.com>
 
 	* config/c6x/c6x-protos.h (c6x_set_return_address): Declare.

gcc/caller-save.c

@@ -198,23 +198,12 @@ init_caller_save (void)
      we can't have the register live over calls.  */
 
   for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
-    {
-      if (call_used_regs[i]
-          && !TEST_HARD_REG_BIT (call_fixed_reg_set, i))
-	{
-	  for (j = 1; j <= MOVE_MAX_WORDS; j++)
-	    {
-	      regno_save_mode[i][j] = HARD_REGNO_CALLER_SAVE_MODE (i, j,
-								   VOIDmode);
-	      if (regno_save_mode[i][j] == VOIDmode && j == 1)
-		{
-		  SET_HARD_REG_BIT (call_fixed_reg_set, i);
-		}
-	    }
-	}
-      else
-	regno_save_mode[i][1] = VOIDmode;
-    }
+    for (j = 1; j <= MOVE_MAX_WORDS; j++)
+      {
+	regno_save_mode[i][j] = HARD_REGNO_CALLER_SAVE_MODE (i, j, VOIDmode);
+	if (regno_save_mode[i][j] == VOIDmode && j == 1)
+	  CLEAR_HARD_REG_BIT (savable_regs, i);
+      }
 
   /* The following code tries to approximate the conditions under which
      we can easily save and restore a register without scratch registers or
@@ -276,7 +265,7 @@ init_caller_save (void)
 	  regno_save_mode[i][j] = VOIDmode;
 	  if (j == 1)
 	    {
-	      SET_HARD_REG_BIT (call_fixed_reg_set, i);
+	      CLEAR_HARD_REG_BIT (savable_regs, i);
 	      if (call_used_regs[i])
 		SET_HARD_REG_BIT (no_caller_save_reg_set, i);
 	    }
@@ -455,8 +444,8 @@ setup_save_areas (void)
       if (SIBLING_CALL_P (insn) && crtl->return_rtx)
 	mark_set_regs (crtl->return_rtx, NULL_RTX, &this_insn_sets);
 
-      used_regs &= ~(call_fixed_reg_set | this_insn_sets);
-      hard_regs_to_save &= used_regs;
+      used_regs &= ~(fixed_reg_set | this_insn_sets);
+      hard_regs_to_save &= used_regs & savable_regs;
       for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
 	if (TEST_HARD_REG_BIT (hard_regs_to_save, regno))
 	  {
@@ -539,8 +528,8 @@ setup_save_areas (void)
 	  if (SIBLING_CALL_P (insn) && crtl->return_rtx)
 	    mark_set_regs (crtl->return_rtx, NULL_RTX, &this_insn_sets);
 
-	  used_regs &= ~(call_fixed_reg_set | this_insn_sets);
-	  hard_regs_to_save &= used_regs;
+	  used_regs &= ~(fixed_reg_set | this_insn_sets);
+	  hard_regs_to_save &= used_regs & savable_regs;
 	  for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
 	    if (TEST_HARD_REG_BIT (hard_regs_to_save, regno))
 	      {
@@ -850,9 +839,10 @@ save_call_clobbered_regs (void)
 	      note_stores (insn, mark_set_regs, &this_insn_sets);
 
 	      /* Compute which hard regs must be saved before this call.  */
-	      hard_regs_to_save &= ~(call_fixed_reg_set
+	      hard_regs_to_save &= ~(fixed_reg_set
 				     | this_insn_sets
 				     | hard_regs_saved);
+	      hard_regs_to_save &= savable_regs;
 	      get_call_reg_set_usage (insn, &call_def_reg_set,
 				      call_used_reg_set);
 	      hard_regs_to_save &= call_def_reg_set;

gcc/config/sh/sh.c

@@ -6707,7 +6707,9 @@ output_stack_adjust (int size, rtx reg, int epilogue_p,
 	    temp = -1;
 	  if (temp < 0 && ! current_function_interrupt && epilogue_p >= 0)
 	    {
-	      HARD_REG_SET temps = call_used_reg_set & ~call_fixed_reg_set;
+	      HARD_REG_SET temps = (call_used_reg_set
+				    & ~fixed_reg_set
+				    & savable_regs);
 	      if (epilogue_p > 0)
 		{
 		  int nreg = 0;

gcc/hard-reg-set.h

@@ -400,11 +400,15 @@ struct target_hard_regs {
   /* The same info as a HARD_REG_SET.  */
   HARD_REG_SET x_call_used_reg_set;
 
-  /* Contains registers that are fixed use -- i.e. in fixed_reg_set -- or
-     a function value return register or TARGET_STRUCT_VALUE_RTX or
-     STATIC_CHAIN_REGNUM.  These are the registers that cannot hold quantities
-     across calls even if we are willing to save and restore them.  */
-  HARD_REG_SET x_call_fixed_reg_set;
+  /* For targets that use reload rather than LRA, this is the set
+     of registers that we are able to save and restore around calls
+     (i.e. those for which we know a suitable mode and set of
+     load/store instructions exist).  For LRA targets it contains
+     all registers.
+
+     This is legacy information and should be removed if all targets
+     switch to LRA.  */
+  HARD_REG_SET x_savable_regs;
 
   /* Contains registers that are fixed use -- i.e. in fixed_reg_set -- but
      only if they are not merely part of that set because they are global
@@ -482,8 +486,8 @@ extern struct target_hard_regs *this_target_hard_regs;
   (this_target_hard_regs->x_call_really_used_regs)
 #define call_used_reg_set \
   (this_target_hard_regs->x_call_used_reg_set)
-#define call_fixed_reg_set \
-  (this_target_hard_regs->x_call_fixed_reg_set)
+#define savable_regs \
+  (this_target_hard_regs->x_savable_regs)
 #define regs_invalidated_by_call \
   (this_target_hard_regs->x_regs_invalidated_by_call)
 #define no_caller_save_reg_set \

gcc/reginfo.c

@@ -351,7 +351,6 @@ init_reg_sets_1 (void)
 
   CLEAR_HARD_REG_SET (fixed_reg_set);
   CLEAR_HARD_REG_SET (call_used_reg_set);
-  CLEAR_HARD_REG_SET (call_fixed_reg_set);
   CLEAR_HARD_REG_SET (regs_invalidated_by_call);
 
   operand_reg_set &= accessible_reg_set;
@@ -417,7 +416,7 @@ init_reg_sets_1 (void)
 	SET_HARD_REG_BIT (regs_invalidated_by_call, i);
     }
 
-  call_fixed_reg_set = fixed_reg_set;
+  SET_HARD_REG_SET (savable_regs);
   fixed_nonglobal_reg_set = fixed_reg_set;
 
   /* Preserve global registers if called more than once.  */
@@ -428,7 +427,6 @@ init_reg_sets_1 (void)
 	  fixed_regs[i] = call_used_regs[i] = 1;
 	  SET_HARD_REG_BIT (fixed_reg_set, i);
 	  SET_HARD_REG_BIT (call_used_reg_set, i);
-	  SET_HARD_REG_BIT (call_fixed_reg_set, i);
 	}
     }
 
@@ -782,7 +780,6 @@ globalize_reg (tree decl, int i)
 
   SET_HARD_REG_BIT (fixed_reg_set, i);
   SET_HARD_REG_BIT (call_used_reg_set, i);
-  SET_HARD_REG_BIT (call_fixed_reg_set, i);
 
   reinit_regs ();
 }