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* [gcc r13-4977] Improve ix86_expand_int_movcc to allow condition (mask) sharing.
@ 2023-01-03 13:42 Roger Sayle
0 siblings, 0 replies; only message in thread
From: Roger Sayle @ 2023-01-03 13:42 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:d0558f420b2a5692fd38ac76ffa97ae6c1726ed9
commit r13-4977-gd0558f420b2a5692fd38ac76ffa97ae6c1726ed9
Author: Roger Sayle <roger@nextmovesoftware.com>
Date: Tue Jan 3 13:40:47 2023 +0000
Improve ix86_expand_int_movcc to allow condition (mask) sharing.
This patch modifies the way that ix86_expand_int_movcc generates RTL,
to allow the condition mask to be shared/reused between multiple
conditional move sequences. Such redundancy is common when RTL
if-conversion transforms non-trivial basic blocks.
As a motivating example, consider the new test case:
int a, b, c, d;
int foo(int x)
{
if (x == 0) {
a = 3;
b = 1;
c = 4;
d = 1;
} else {
a = 5;
b = 9;
c = 2;
d = 7;
}
return x;
}
This is currently compiled, with -O2, to:
foo: cmpl $1, %edi
movl %edi, %eax
sbbl %edi, %edi
andl $-2, %edi
addl $5, %edi
cmpl $1, %eax
sbbl %esi, %esi
movl %edi, a(%rip)
andl $-8, %esi
addl $9, %esi
cmpl $1, %eax
sbbl %ecx, %ecx
movl %esi, b(%rip)
andl $2, %ecx
addl $2, %ecx
cmpl $1, %eax
sbbl %edx, %edx
movl %ecx, c(%rip)
andl $-6, %edx
addl $7, %edx
movl %edx, d(%rip)
ret
Notice that the if-then-else blocks have been if-converted into four
conditional move sequences/assignments, each consisting of cmpl, sbbl,
andl and addl. However, as the conditions are the same, the cmpl and
sbbl instructions used to generate the mask could be shared by CSE.
This patch enables that so that we now generate:
foo: cmpl $1, %edi
movl %edi, %eax
sbbl %edx, %edx
movl %edx, %edi
movl %edx, %esi
movl %edx, %ecx
andl $-6, %edx
andl $-2, %edi
andl $-8, %esi
andl $2, %ecx
addl $7, %edx
addl $5, %edi
addl $9, %esi
addl $2, %ecx
movl %edx, d(%rip)
movl %edi, a(%rip)
movl %esi, b(%rip)
movl %ecx, c(%rip)
ret
Notice, the code now contains only a single cmpl and a single sbbl,
with result being shared (via movl).
2023-01-03 Roger Sayle <roger@nextmovesoftware.com>
gcc/ChangeLog
* config/i386/i386-expand.cc (ix86_expand_int_movcc): Rewrite
RTL expansion to allow condition (mask) to be shared/reused,
by avoiding overwriting pseudos and adding REG_EQUAL notes.
gcc/testsuite/ChangeLog
* gcc.target/i386/cmov10.c: New test case.
Diff:
---
gcc/config/i386/i386-expand.cc | 46 +++++++++++++++-------------------
gcc/testsuite/gcc.target/i386/cmov10.c | 21 ++++++++++++++++
2 files changed, 41 insertions(+), 26 deletions(-)
diff --git a/gcc/config/i386/i386-expand.cc b/gcc/config/i386/i386-expand.cc
index 3eddbc94360..4fd7c3ccd91 100644
--- a/gcc/config/i386/i386-expand.cc
+++ b/gcc/config/i386/i386-expand.cc
@@ -3284,8 +3284,8 @@ ix86_expand_int_movcc (rtx operands[])
|| negate_cc_compare_p
|| ix86_expand_carry_flag_compare (code, op0, op1, &compare_op))
{
- /* Detect overlap between destination and compare sources. */
- rtx tmp = out;
+ /* Place comparison result in its own pseudo. */
+ rtx tmp = gen_reg_rtx (mode);
if (negate_cc_compare_p)
{
@@ -3295,7 +3295,6 @@ ix86_expand_int_movcc (rtx operands[])
emit_insn (gen_x86_negsi_ccc (gen_reg_rtx (SImode),
gen_lowpart (SImode, op0)));
- tmp = gen_reg_rtx (mode);
if (mode == DImode)
emit_insn (gen_x86_movdicc_0_m1_neg (tmp));
else
@@ -3337,9 +3336,6 @@ ix86_expand_int_movcc (rtx operands[])
}
diff = ct - cf;
- if (reg_overlap_mentioned_p (out, compare_op))
- tmp = gen_reg_rtx (mode);
-
if (mode == DImode)
emit_insn (gen_x86_movdicc_0_m1 (tmp, flags, compare_op));
else
@@ -3358,6 +3354,11 @@ ix86_expand_int_movcc (rtx operands[])
tmp = emit_store_flag (tmp, code, op0, op1, VOIDmode, 0, -1);
}
+ /* Add a REG_EQUAL note to allow condition to be shared. */
+ rtx note = gen_rtx_fmt_ee (code, mode, op0, op1);
+ set_unique_reg_note (get_last_insn (), REG_EQUAL,
+ gen_rtx_NEG (mode, note));
+
if (diff == 1)
{
/*
@@ -3368,9 +3369,8 @@ ix86_expand_int_movcc (rtx operands[])
* Size 5 - 8.
*/
if (ct)
- tmp = expand_simple_binop (mode, PLUS,
- tmp, GEN_INT (ct),
- copy_rtx (tmp), 1, OPTAB_DIRECT);
+ tmp = expand_simple_binop (mode, PLUS, tmp, GEN_INT (ct),
+ NULL_RTX, 1, OPTAB_DIRECT);
}
else if (cf == -1)
{
@@ -3381,9 +3381,8 @@ ix86_expand_int_movcc (rtx operands[])
*
* Size 8.
*/
- tmp = expand_simple_binop (mode, IOR,
- tmp, GEN_INT (ct),
- copy_rtx (tmp), 1, OPTAB_DIRECT);
+ tmp = expand_simple_binop (mode, IOR, tmp, GEN_INT (ct),
+ NULL_RTX, 1, OPTAB_DIRECT);
}
else if (diff == -1 && ct)
{
@@ -3395,11 +3394,10 @@ ix86_expand_int_movcc (rtx operands[])
*
* Size 8 - 11.
*/
- tmp = expand_simple_unop (mode, NOT, tmp, copy_rtx (tmp), 1);
+ tmp = expand_simple_unop (mode, NOT, tmp, NULL_RTX, 1);
if (cf)
- tmp = expand_simple_binop (mode, PLUS,
- copy_rtx (tmp), GEN_INT (cf),
- copy_rtx (tmp), 1, OPTAB_DIRECT);
+ tmp = expand_simple_binop (mode, PLUS, tmp, GEN_INT (cf),
+ NULL_RTX, 1, OPTAB_DIRECT);
}
else
{
@@ -3417,22 +3415,18 @@ ix86_expand_int_movcc (rtx operands[])
{
cf = ct;
ct = 0;
- tmp = expand_simple_unop (mode, NOT, tmp, copy_rtx (tmp), 1);
+ tmp = expand_simple_unop (mode, NOT, tmp, NULL_RTX, 1);
}
- tmp = expand_simple_binop (mode, AND,
- copy_rtx (tmp),
+ tmp = expand_simple_binop (mode, AND, tmp,
gen_int_mode (cf - ct, mode),
- copy_rtx (tmp), 1, OPTAB_DIRECT);
+ NULL_RTX, 1, OPTAB_DIRECT);
if (ct)
- tmp = expand_simple_binop (mode, PLUS,
- copy_rtx (tmp), GEN_INT (ct),
- copy_rtx (tmp), 1, OPTAB_DIRECT);
+ tmp = expand_simple_binop (mode, PLUS, tmp, GEN_INT (ct),
+ NULL_RTX, 1, OPTAB_DIRECT);
}
- if (!rtx_equal_p (tmp, out))
- emit_move_insn (copy_rtx (out), copy_rtx (tmp));
-
+ emit_move_insn (out, tmp);
return true;
}
diff --git a/gcc/testsuite/gcc.target/i386/cmov10.c b/gcc/testsuite/gcc.target/i386/cmov10.c
new file mode 100644
index 00000000000..142b4d7d051
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/cmov10.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+int a, b, c, d;
+
+int foo(int x)
+{
+ if (x == 0) {
+ a = 3;
+ b = 1;
+ c = 4;
+ d = 1;
+ } else {
+ a = 5;
+ b = 9;
+ c = 2;
+ d = 7;
+ }
+ return x;
+}
+/* { dg-final { scan-assembler-times "cmpl" 1 } } */
+/* { dg-final { scan-assembler-times "sbbl" 1 } } */
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