[sparc] Rotate stack checking loop

[Eric Botcazou <ebotcazou@adacore.com>]

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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).

Tested on SPARC/Solaris, to be applied on the mainline.


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

	* config/sparc/sparc.c (sparc_emit_probe_stack_range): Adjust.
	(output_probe_stack_range): Rotate the loop and simplify.

-- 
Eric Botcazou

[-- Attachment #2: rotate_sparc.diff --]
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Index: config/sparc/sparc.c
===================================================================
--- config/sparc/sparc.c	(revision 230204)
+++ config/sparc/sparc.c	(working copy)
@@ -5058,9 +5058,9 @@ sparc_emit_probe_stack_range (HOST_WIDE_
       emit_stack_probe (plus_constant (Pmode, g1, -size));
     }
 
-  /* The run-time loop is made up of 10 insns in the generic case while the
+  /* The run-time loop is made up of 9 insns in the generic case while the
      compile-time loop is made up of 4+2*(n-2) insns for n # of intervals.  */
-  else if (size <= 5 * PROBE_INTERVAL)
+  else if (size <= 4 * PROBE_INTERVAL)
     {
       HOST_WIDE_INT i;
 
@@ -5147,41 +5147,33 @@ const char *
 output_probe_stack_range (rtx reg1, rtx reg2)
 {
   static int labelno = 0;
-  char loop_lab[32], end_lab[32];
+  char loop_lab[32];
   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.  */
+  /* TEST_ADDR = TEST_ADDR + PROBE_INTERVAL.  */
   xops[0] = reg1;
+  xops[1] = GEN_INT (-PROBE_INTERVAL);
+  output_asm_insn ("add\t%0, %1, %0", xops);
+
+  /* Test if TEST_ADDR == LAST_ADDR.  */
   xops[1] = reg2;
   output_asm_insn ("cmp\t%0, %1", xops);
-  if (TARGET_ARCH64)
-    fputs ("\tbe,pn\t%xcc,", asm_out_file);
-  else
-    fputs ("\tbe\t", asm_out_file);
-  assemble_name_raw (asm_out_file, end_lab);
-  fputc ('\n', asm_out_file);
-
-  /* TEST_ADDR = TEST_ADDR + PROBE_INTERVAL.  */
-  xops[1] = GEN_INT (-PROBE_INTERVAL);
-  output_asm_insn (" add\t%0, %1, %0", xops);
 
   /* Probe at TEST_ADDR and branch.  */
   if (TARGET_ARCH64)
-    fputs ("\tba,pt\t%xcc,", asm_out_file);
+    fputs ("\tbne,pt\t%xcc,", asm_out_file);
   else
-    fputs ("\tba\t", asm_out_file);
+    fputs ("\tbne\t", asm_out_file);
   assemble_name_raw (asm_out_file, loop_lab);
   fputc ('\n', asm_out_file);
   xops[1] = GEN_INT (SPARC_STACK_BIAS);
   output_asm_insn (" st\t%%g0, [%0+%1]", xops);
 
-  ASM_OUTPUT_INTERNAL_LABEL (asm_out_file, end_lab);
-
   return "";
 }