RE: [mips] Rotate stack checking loop

[Moore, Catherine]

> -Original Message-
> From: gcc-patches-ow...@gcc.gnu.org [mailto:gcc-patches-
> ow...@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  <ebotca...@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.

[mips] Rotate stack checking loop

[Eric Botcazou]

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  

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

-- 
Eric BotcazouIndex: 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, "%(%