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[RS6000] Stack tie fix.


This patch merges the rs6000 stack_tie and frame_tie rtl, so that we
now should use a tie insn that mentions all base regs involved in
register saves and restores.  That should avoid any alias analysis
problems eg. http://gcc.gnu.org/ml/gcc-patches/2011-11/msg01156.html.
I chose to put the regs of interest on the destination of the fake
set, rather than in the source as is currently done, because I figure
that relying on the compiler to not reorder reads is fragile.  Here's
an example of the new stack tie:

(set (mem:BLK (unspec:SI [(reg:SI 1) (reg:SI 12)] UNSPEC_TIE))
     (const_int 0))

Some notes:
- I tried putting the mem on both source and destination of the set,
  but that runs afoul of rtl dead code elimination.
- The rs6000_emit_epilogue places that called gen_frame_tie and
  gen_stack_tie both used alias set 0 mems.  I believe this was
  unnecessarily restrictive.
- CODE_FOR_stack_tie is mentioned in rs6000.c but not
  CODE_FOR_frame_tie.  Removing frame_tie fixes this sched bug too.

Bootstrapped and regression tested powerpc-linux with usual -O2
BOOT_CFLAGS and also -Os, and testcases from pr44199, pr30282, pr52828,
the url above and http://gcc.gnu.org/ml/gcc/2011-03/msg00123.html
examined for sanity.  OK to apply?

	PR target/52828
	* config/rs6000/rs6000.c (rs6000_emit_stack_tie): Rewrite with
	tie regs on destination of set.  Delete forward declaration.
	(rs6000_emit_stack_reset): Update rs6000_emit_stack_tie calls.
	(rs6000_emit_prologue): Likewise.
	(rs6000_emit_epilogue): Likewise.  Use in place of gen_frame_tie
	and gen_stack_tie.
	* config/rs6000/predicates.md (tie_operand): New.
	* config/rs6000/rs6000.md (restore_stack_block): Generate new
	stack tie rtl.
	(restore_stack_nonlocal): Likewise.
	(stack_tie): Update.
	(frame_tie): Delete.

Index: gcc/config/rs6000/rs6000.c
===================================================================
--- gcc/config/rs6000/rs6000.c	(revision 185830)
+++ gcc/config/rs6000/rs6000.c	(working copy)
@@ -925,7 +925,6 @@ static const char *rs6000_invalid_within_doloop (c
 static bool rs6000_legitimate_address_p (enum machine_mode, rtx, bool);
 static bool rs6000_debug_legitimate_address_p (enum machine_mode, rtx, bool);
 static rtx rs6000_generate_compare (rtx, enum machine_mode);
-static void rs6000_emit_stack_tie (void);
 static bool spe_func_has_64bit_regs_p (void);
 static rtx gen_frame_mem_offset (enum machine_mode, rtx, int);
 static unsigned rs6000_hash_constant (rtx);
@@ -18517,12 +18516,28 @@ rs6000_aix_asm_output_dwarf_table_ref (char * fram
    and the change to the stack pointer.  */
 
 static void
-rs6000_emit_stack_tie (void)
+rs6000_emit_stack_tie (rtx fp, bool hard_frame_needed)
 {
-  rtx mem = gen_frame_mem (BLKmode,
-			   gen_rtx_REG (Pmode, STACK_POINTER_REGNUM));
+  rtx u;
+  rtvec p;
+  int i;
 
-  emit_insn (gen_stack_tie (mem));
+  if (REGNO (fp) == STACK_POINTER_REGNUM
+      || (hard_frame_needed
+	  && REGNO (fp) == HARD_FRAME_POINTER_REGNUM))
+    fp = NULL_RTX;
+
+  p = rtvec_alloc (1 + hard_frame_needed + (fp != NULL_RTX));
+
+  i = 0;
+  RTVEC_ELT (p, i++) = gen_rtx_REG (Pmode, STACK_POINTER_REGNUM);
+  if (hard_frame_needed)
+    RTVEC_ELT (p, i++) = gen_rtx_REG (Pmode, HARD_FRAME_POINTER_REGNUM);
+  if (fp != NULL_RTX)
+    RTVEC_ELT (p, i++) = fp;
+  u = gen_rtx_UNSPEC (Pmode, p, UNSPEC_TIE);
+
+  emit_insn (gen_stack_tie (gen_frame_mem (BLKmode, u)));
 }
 
 /* Emit the correct code for allocating stack space, as insns.
@@ -19142,7 +19157,7 @@ rs6000_emit_stack_reset (rs6000_stack_t *info,
       || (TARGET_SPE_ABI
 	  && info->spe_64bit_regs_used != 0
 	  && info->first_gp_reg_save != 32))
-    rs6000_emit_stack_tie ();
+    rs6000_emit_stack_tie (frame_reg_rtx, frame_pointer_needed);
   
   if (frame_reg_rtx != sp_reg_rtx)
     {
@@ -19362,7 +19377,7 @@ rs6000_emit_prologue (void)
 	}
       rs6000_emit_allocate_stack (info->total_size, copy_reg);
       if (frame_reg_rtx != sp_reg_rtx)
-	rs6000_emit_stack_tie ();
+	rs6000_emit_stack_tie (frame_reg_rtx, false);
     }
 
   /* Handle world saves specially here.  */
@@ -19866,7 +19881,7 @@ rs6000_emit_prologue (void)
 	sp_offset = info->total_size;
       rs6000_emit_allocate_stack (info->total_size, copy_reg);
       if (frame_reg_rtx != sp_reg_rtx)
-	rs6000_emit_stack_tie ();
+	rs6000_emit_stack_tie (frame_reg_rtx, false);
     }
 
   /* Set frame pointer, if needed.  */
@@ -20437,13 +20452,7 @@ rs6000_emit_epilogue (int sibcall)
       /* Prevent reordering memory accesses against stack pointer restore.  */
       else if (cfun->calls_alloca
 	       || offset_below_red_zone_p (-info->total_size))
-	{
-	  rtx mem1 = gen_rtx_MEM (BLKmode, hard_frame_pointer_rtx);
-	  rtx mem2 = gen_rtx_MEM (BLKmode, sp_reg_rtx);
-	  MEM_NOTRAP_P (mem1) = 1;
-	  MEM_NOTRAP_P (mem2) = 1;
-	  emit_insn (gen_frame_tie (mem1, mem2));
-	}
+	rs6000_emit_stack_tie (frame_reg_rtx, true);
 
       insn = emit_insn (gen_add3_insn (frame_reg_rtx, hard_frame_pointer_rtx,
 				       GEN_INT (info->total_size)));
@@ -20456,11 +20465,7 @@ rs6000_emit_epilogue (int sibcall)
       /* Prevent reordering memory accesses against stack pointer restore.  */
       if (cfun->calls_alloca
 	  || offset_below_red_zone_p (-info->total_size))
-	{
-	  rtx mem = gen_rtx_MEM (BLKmode, sp_reg_rtx);
-	  MEM_NOTRAP_P (mem) = 1;
-	  emit_insn (gen_stack_tie (mem));
-	}
+	rs6000_emit_stack_tie (frame_reg_rtx, false);
       insn = emit_insn (gen_add3_insn (sp_reg_rtx, sp_reg_rtx,
 				       GEN_INT (info->total_size)));
       sp_offset = 0;
Index: gcc/config/rs6000/predicates.md
===================================================================
--- gcc/config/rs6000/predicates.md	(revision 185830)
+++ gcc/config/rs6000/predicates.md	(working copy)
@@ -1451,3 +1451,11 @@
 
   return 1;
 })
+
+;; Return 1 if OP is a stack tie operand.
+(define_predicate "tie_operand"
+  (match_code "mem")
+{
+  return (GET_CODE (XEXP (op, 0)) == UNSPEC
+	  && XINT (XEXP (op, 0), 1) == UNSPEC_TIE);
+})
Index: gcc/config/rs6000/rs6000.md
===================================================================
--- gcc/config/rs6000/rs6000.md	(revision 185830)
+++ gcc/config/rs6000/rs6000.md	(working copy)
@@ -11989,17 +11989,20 @@
 (define_expand "restore_stack_block"
   [(set (match_dup 2) (match_dup 3))
    (set (match_dup 4) (match_dup 2))
-   (set (match_dup 5) (unspec:BLK [(match_dup 5)] UNSPEC_TIE))
+   (set (match_dup 5) (const_int 0))
    (set (match_operand 0 "register_operand" "")
 	(match_operand 1 "register_operand" ""))]
   ""
   "
 {
+  rtx u;
+
   operands[1] = force_reg (Pmode, operands[1]);
   operands[2] = gen_reg_rtx (Pmode);
   operands[3] = gen_frame_mem (Pmode, operands[0]);
   operands[4] = gen_frame_mem (Pmode, operands[1]);
-  operands[5] = gen_frame_mem (BLKmode, operands[0]);
+  u = gen_rtx_UNSPEC (Pmode, gen_rtvec (1, operands[0]), UNSPEC_TIE);
+  operands[5] = gen_frame_mem (BLKmode, u);
 }")
 
 (define_expand "save_stack_nonlocal"
@@ -12022,12 +12025,13 @@
   [(set (match_dup 2) (match_operand 1 "memory_operand" ""))
    (set (match_dup 3) (match_dup 4))
    (set (match_dup 5) (match_dup 2))
-   (set (match_dup 6) (unspec:BLK [(match_dup 6)] UNSPEC_TIE))
+   (set (match_dup 6) (const_int 0))
    (set (match_operand 0 "register_operand" "") (match_dup 3))]
   ""
   "
 {
   int units_per_word = (TARGET_32BIT) ? 4 : 8;
+  rtx u;
 
   /* Restore the backchain from the first word, sp from the second.  */
   operands[2] = gen_reg_rtx (Pmode);
@@ -12035,7 +12039,8 @@
   operands[1] = adjust_address_nv (operands[1], Pmode, 0);
   operands[4] = adjust_address_nv (operands[1], Pmode, units_per_word);
   operands[5] = gen_frame_mem (Pmode, operands[3]);
-  operands[6] = gen_frame_mem (BLKmode, operands[0]);
+  u = gen_rtx_UNSPEC (Pmode, gen_rtvec (1, operands[0]), UNSPEC_TIE);
+  operands[6] = gen_frame_mem (BLKmode, u);
 }")
 
 ;; TOC register handling.
@@ -15899,25 +15904,15 @@
   [(set_attr "type" "branch")
    (set_attr "length" "4")])
 
-; These are to explain that changes to the stack pointer should
-; not be moved over stores to stack memory.
+; This is to explain that changes to the stack pointer should
+; not be moved over loads from or stores to stack memory.
 (define_insn "stack_tie"
-  [(set (match_operand:BLK 0 "memory_operand" "+m")
-        (unspec:BLK [(match_dup 0)] UNSPEC_TIE))]
+  [(set (match_operand:BLK 0 "tie_operand" "")
+	(const_int 0))]
   ""
   ""
   [(set_attr "length" "0")])
 
-; Like stack_tie, but depend on both fp and sp based memory.
-(define_insn "frame_tie"
-  [(set (match_operand:BLK 0 "memory_operand" "+m")
-	(unspec:BLK [(match_dup 0)
-		     (match_operand:BLK 1 "memory_operand" "m")] UNSPEC_TIE))]
-  ""
-  ""
-  [(set_attr "length" "0")])
-
-
 (define_expand "epilogue"
   [(use (const_int 0))]
   ""

-- 
Alan Modra
Australia Development Lab, IBM


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