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).
The patch also changes a mov+sub pair into an lea in the common case on Linux,
saving one more instruction in the process.
Tested on x86/Linux & x86-64/Linux (ix86_adjust_stack_and_probe path) and
x86/Solaris (ix86_emit_probe_stack_range path). OK for the mainline?
2015-11-12 Eric Botcazou
* config/i386/i386.c (ix86_adjust_stack_and_probe): Adjust and use
an lea instruction when possible.
(output_adjust_stack_and_probe): Rotate the loop and simplify.
(ix86_emit_probe_stack_range): Adjust.
(output_probe_stack_range): Rotate the loop and simplify.
--
Eric BotcazouIndex: config/i386/i386.c
===
--- config/i386/i386.c (revision 230245)
+++ config/i386/i386.c (working copy)
@@ -12137,10 +12137,10 @@ ix86_adjust_stack_and_probe (const HOST_
rtx size_rtx = GEN_INT (size), last;
/* See if we have a constant small number of probes to generate. If so,
- that's the easy case. The run-time loop is made up of 11 insns in the
+ that's the easy case. The run-time loop is made up of 9 insns in the
generic case while the compile-time loop is made up of 3+2*(n-1) insns
for n # of intervals. */
- if (size <= 5 * PROBE_INTERVAL)
+ if (size <= 4 * PROBE_INTERVAL)
{
HOST_WIDE_INT i, adjust;
bool first_probe = true;
@@ -12207,19 +12207,27 @@ ix86_adjust_stack_and_probe (const HOST_
- (PROBE_INTERVAL + dope;
/* LAST_ADDR = SP_0 + PROBE_INTERVAL + ROUNDED_SIZE. */
- emit_move_insn (sr.reg, GEN_INT (-rounded_size));
- emit_insn (gen_rtx_SET (sr.reg,
- gen_rtx_PLUS (Pmode, sr.reg,
- stack_pointer_rtx)));
+ if (rounded_size <= (HOST_WIDE_INT_1 << 31))
+ emit_insn (gen_rtx_SET (sr.reg,
+plus_constant (Pmode, stack_pointer_rtx,
+ -rounded_size)));
+ else
+ {
+ emit_move_insn (sr.reg, GEN_INT (-rounded_size));
+ emit_insn (gen_rtx_SET (sr.reg,
+ gen_rtx_PLUS (Pmode, sr.reg,
+ stack_pointer_rtx)));
+ }
/* Step 3: the loop
- while (SP != LAST_ADDR)
+ do
{
SP = SP + PROBE_INTERVAL
probe at SP
}
+ while (SP != LAST_ADDR)
adjusts SP and probes to PROBE_INTERVAL + N * PROBE_INTERVAL for
values of N from 1 until it is equal to ROUNDED_SIZE. */
@@ -12275,23 +12283,16 @@ const char *
output_adjust_stack_and_probe (rtx reg)
{
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 SP == LAST_ADDR. */
- xops[0] = stack_pointer_rtx;
- xops[1] = reg;
- output_asm_insn ("cmp%z0\t{%1, %0|%0, %1}", xops);
- fputs ("\tje\t", asm_out_file);
- assemble_name_raw (asm_out_file, end_lab);
- fputc ('\n', asm_out_file);
-
/* SP = SP + PROBE_INTERVAL. */
+ xops[0] = stack_pointer_rtx;
xops[1] = GEN_INT (PROBE_INTERVAL);
output_asm_insn ("sub%z0\t{%1, %0|%0, %1}", xops);
@@ -12299,12 +12300,16 @@ output_adjust_stack_and_probe (rtx reg)
xops[1] = const0_rtx;
output_asm_insn ("or%z0\t{%1, (%0)|DWORD PTR [%0], %1}", xops);
- fprintf (asm_out_file, "\tjmp\t");
+ /* Test if SP == LAST_ADDR. */
+ xops[0] = stack_pointer_rtx;
+ xops[1] = reg;
+ output_asm_insn ("cmp%z0\t{%1, %0|%0, %1}", xops);
+
+ /* Branch. */
+ fputs ("\tjne\t", asm_out_file);
assemble_name_raw (asm_out_file, loop_lab);
fputc ('\n', asm_out_file);
- ASM_OUTPUT_INTERNAL_LABEL (asm_out_file, end_lab);
-
return "";
}
@@ -12315,10 +12320,10 @@ static void
ix86_emit_probe_stack_range (HOST_WIDE_INT first, HOST_WIDE_INT size)
{
/* See if we have a constant small number of probes to generate. If so,
- that's the easy case. The run-time loop is made up of 7 insns in the
+ that's the easy case. The run-time loop is made up of 6 insns in the
generic case while the compile-time loop is made up of n insns for n #
of intervals. */
- if (size <= 7 * PROBE_INTERVAL)
+ if (size <= 6 * PROBE_INTERVAL)
{
HOST_WIDE_INT i;
@@ -12362,11 +12367,12 @@ ix86_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
