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* [mips] Rotate stack checking loop
@ 2015-11-12 21:52 Eric Botcazou
  2015-12-02 15:36 ` Moore, Catherine
  0 siblings, 1 reply; 2+ messages in thread
From: Eric Botcazou @ 2015-11-12 21:52 UTC (permalink / raw)
  To: gcc-patches

[-- Attachment #1: Type: text/plain, Size: 744 bytes --]

Hi,

this patch rotates the loop generated in the prologue to do stack checking 
when -fstack-check is specified, thereby saving one branch instruction.  It 
was initially implemented as a WHILE loop to match the generic implementation 
but can be turned into a DO-WHILE loop because the amount of stack to be 
checked is known at compile time (since it's the static part of the frame).

Unfortunately I don't have access to MIPS hardware any more so I only verified 
that the assembly code is as expected and can be assembled.   OK for mainline?


2015-11-12  Eric Botcazou  <ebotcazou@adacore.com>

	* config/mips/mips.c (mips_emit_probe_stack_range): Adjust.
	(mips_output_probe_stack_range): Rotate the loop and simplify.

-- 
Eric Botcazou

[-- Attachment #2: rotate_mips.diff --]
[-- Type: text/x-patch, Size: 1981 bytes --]

Index: config/mips/mips.c
===================================================================
--- config/mips/mips.c	(revision 230204)
+++ config/mips/mips.c	(working copy)
@@ -11335,11 +11335,12 @@ mips_emit_probe_stack_range (HOST_WIDE_I
 
       /* Step 3: the loop
 
-	while (TEST_ADDR != LAST_ADDR)
+	do
 	  {
 	    TEST_ADDR = TEST_ADDR + PROBE_INTERVAL
 	    probe at TEST_ADDR
 	  }
+	while (TEST_ADDR != LAST_ADDR)
 
 	probes at FIRST + N * PROBE_INTERVAL for values of N from 1
 	until it is equal to ROUNDED_SIZE.  */
@@ -11365,38 +11366,31 @@ const char *
 mips_output_probe_stack_range (rtx reg1, rtx reg2)
 {
   static int labelno = 0;
-  char loop_lab[32], end_lab[32], tmp[64];
+  char loop_lab[32], tmp[64];
   rtx xops[2];
 
-  ASM_GENERATE_INTERNAL_LABEL (loop_lab, "LPSRL", labelno);
-  ASM_GENERATE_INTERNAL_LABEL (end_lab, "LPSRE", labelno++);
+  ASM_GENERATE_INTERNAL_LABEL (loop_lab, "LPSRL", labelno++);
 
+  /* Loop.  */
   ASM_OUTPUT_INTERNAL_LABEL (asm_out_file, loop_lab);
 
-  /* Jump to END_LAB if TEST_ADDR == LAST_ADDR.  */
-  xops[0] = reg1;
-  xops[1] = reg2;
-  strcpy (tmp, "%(%<beq\t%0,%1,");
-  output_asm_insn (strcat (tmp, &end_lab[1]), xops);
- 
   /* TEST_ADDR = TEST_ADDR + PROBE_INTERVAL.  */
+  xops[0] = reg1;
   xops[1] = GEN_INT (-PROBE_INTERVAL);
   if (TARGET_64BIT && TARGET_LONG64)
     output_asm_insn ("daddiu\t%0,%0,%1", xops);
   else
     output_asm_insn ("addiu\t%0,%0,%1", xops);
 
-  /* Probe at TEST_ADDR and branch.  */
-  fprintf (asm_out_file, "\tb\t");
-  assemble_name_raw (asm_out_file, loop_lab);
-  fputc ('\n', asm_out_file);
+  /* Probe at TEST_ADDR, test if TEST_ADDR == LAST_ADDR and branch.  */
+  xops[1] = reg2;
+  strcpy (tmp, "%(%<bne\t%0,%1,");
+  output_asm_insn (strcat (tmp, &loop_lab[1]), xops); 
   if (TARGET_64BIT)
     output_asm_insn ("sd\t$0,0(%0)%)", xops);
   else
     output_asm_insn ("sw\t$0,0(%0)%)", xops);
 
-  ASM_OUTPUT_INTERNAL_LABEL (asm_out_file, end_lab);
-
   return "";
 }
 

^ permalink raw reply	[flat|nested] 2+ messages in thread

* RE: [mips] Rotate stack checking loop
  2015-11-12 21:52 [mips] Rotate stack checking loop Eric Botcazou
@ 2015-12-02 15:36 ` Moore, Catherine
  0 siblings, 0 replies; 2+ messages in thread
From: Moore, Catherine @ 2015-12-02 15:36 UTC (permalink / raw)
  To: Eric Botcazou, gcc-patches; +Cc: Matthew Fortune



> -----Original Message-----
> From: gcc-patches-owner@gcc.gnu.org [mailto:gcc-patches-
> owner@gcc.gnu.org] On Behalf Of Eric Botcazou
> Sent: Thursday, November 12, 2015 4:51 PM
> To: gcc-patches@gcc.gnu.org
> Subject: [mips] Rotate stack checking loop
> 
> Hi,
> 
> this patch rotates the loop generated in the prologue to do stack checking
> when -fstack-check is specified, thereby saving one branch instruction.  It
> was initially implemented as a WHILE loop to match the generic
> implementation but can be turned into a DO-WHILE loop because the
> amount of stack to be checked is known at compile time (since it's the static
> part of the frame).
> 
> Unfortunately I don't have access to MIPS hardware any more so I only
> verified
> that the assembly code is as expected and can be assembled.   OK for
> mainline?
> 
> 
> 2015-11-12  Eric Botcazou  <ebotcazou@adacore.com>
> 
> 	* config/mips/mips.c (mips_emit_probe_stack_range): Adjust.
> 	(mips_output_probe_stack_range): Rotate the loop and simplify.
> 
This is OK.

^ permalink raw reply	[flat|nested] 2+ messages in thread

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