Hi all,
This patch is a sequel to:
https://gcc.gnu.org/ml/gcc-patches/2015-07/msg02567.html
It allows if-conversion of expressions of the form:
if (test) x := y + c1; else x := y + c2
where c1 and c2 are a pair constants that can be optimised using the
existing rules in noce_try_store_flag_constants.
The resulting sequence looks something like:
x := (test [!=,==] 0) + y;
x := x + [c1,c2];
This patch reuses the logic for the combinations of diff and STORE_FLAG signs
that
is hammered out in https://gcc.gnu.org/ml/gcc-patches/2015-07/msg02567.html.
That means we just extract the constants c1 and c2 from the PLUS rtx
and use their diff as the driver for the logic in that function.
Currently, this patch allows only the case where
diff == STORE_FLAG_VALUE || diff == -STORE_FLAG_VALUE
as it is the most beneficial case (from looking at SPEC2006 on aarch64)
and also the least tricky to get right.
In the future I suppose that restriction can be relaxed if needed, but in any
case
this should be an improvement over the existing situation.
On aarch64 this allows us for code:
int
barsi (int x)
{
return x > 100 ? x + 4 : x + 3;
}
to generate:
barsi:
cmp w0, 101
cinc w0, w0, ge
add w0, w0, 3
ret
instead of the current:
barsi:
add w1, w0, 4
add w2, w0, 3
cmp w0, 101
csel w0, w2, w1, lt
ret
thus saving one instruction and using two fewer registers.
Bootstrapped and tested on arm, aarch64, x86_64.
Ok for trunk?
Thanks,
Kyrill
2015-08-12 Kyrylo Tkachov <kyrylo.tkac...@arm.com>
* ifcvt.c (noce_try_store_flag_constants): Handle PLUS-immediate
expressions in A and B.
2015-08-12 Kyrylo Tkachov <kyrylo.tkac...@arm.com>
* gcc.target/aarch64/cinc_common_1.c: New test.
commit ce0de8d30962bf00339dc3a030401a4be2a7a248
Author: Kyrylo Tkachov <kyrylo.tkac...@arm.com>
Date: Thu Jul 30 15:14:27 2015 +0100
[ifcvt][unfinished] Allow PLUS+immediate expression in noce_try_store_flag_constants
diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
index f815166..7a44e29 100644
--- a/gcc/ifcvt.c
+++ b/gcc/ifcvt.c
@@ -1198,17 +1198,35 @@ noce_try_store_flag_constants (struct noce_if_info *if_info)
HOST_WIDE_INT itrue, ifalse, diff, tmp;
int normalize;
bool can_reverse;
- machine_mode mode;
+ machine_mode mode = GET_MODE (if_info->x);;
+ rtx common = NULL_RTX;
if (!noce_simple_bbs (if_info))
return FALSE;
- if (CONST_INT_P (if_info->a)
- && CONST_INT_P (if_info->b))
+ rtx a = if_info->a;
+ rtx b = if_info->b;
+
+ /* Handle cases like x := test ? y + 3 : y + 4. */
+ if (GET_CODE (a) == PLUS
+ && GET_CODE (b) == PLUS
+ && CONST_INT_P (XEXP (a, 1))
+ && CONST_INT_P (XEXP (b, 1))
+ && rtx_equal_p (XEXP (a, 0), XEXP (b, 0))
+ && noce_operand_ok (XEXP (a, 0))
+ && if_info->branch_cost >= 2)
{
- mode = GET_MODE (if_info->x);
- ifalse = INTVAL (if_info->a);
- itrue = INTVAL (if_info->b);
+ common = XEXP (a, 0);
+
+ a = XEXP (a, 1);
+ b = XEXP (b, 1);
+ }
+
+ if (CONST_INT_P (a)
+ && CONST_INT_P (b))
+ {
+ ifalse = INTVAL (a);
+ itrue = INTVAL (b);
bool subtract_flag_p = false;
diff = (unsigned HOST_WIDE_INT) itrue - ifalse;
@@ -1241,6 +1259,11 @@ noce_try_store_flag_constants (struct noce_if_info *if_info)
{
reversep = can_reverse;
subtract_flag_p = !can_reverse;
+ /* If we need to subtract the flag and we have PLUS-immediate
+ A and B then it is unlikely to be beneficial to play tricks
+ here. */
+ if (subtract_flag_p && common)
+ return FALSE;
}
/* test ? 3 : 4
=> can_reverse | 3 + (test == 0)
@@ -1249,6 +1272,11 @@ noce_try_store_flag_constants (struct noce_if_info *if_info)
{
reversep = can_reverse;
subtract_flag_p = !can_reverse;
+ /* If we need to subtract the flag and we have PLUS-immediate
+ A and B then it is unlikely to be beneficial to play tricks
+ here. */
+ if (subtract_flag_p && common)
+ return FALSE;
}
/* test ? 4 : 3
=> 4 + (test != 0). */
@@ -1290,6 +1318,15 @@ noce_try_store_flag_constants (struct noce_if_info *if_info)
}
start_sequence ();
+
+ /* If we have x := test ? x + 3 : x + 4 then move the original
+ x out of the way while we store flags. */
+ if (common && rtx_equal_p (common, if_info->x))
+ {
+ common = gen_reg_rtx (mode);
+ noce_emit_move_insn (common, if_info->x);
+ }
+
target = noce_emit_store_flag (if_info, if_info->x, reversep, normalize);
if (! target)
{
@@ -1301,13 +1338,27 @@ noce_try_store_flag_constants (struct noce_if_info *if_info)
=> x = 3 + (test == 0); */
if (diff == STORE_FLAG_VALUE || diff == -STORE_FLAG_VALUE)
{
+ /* Add the common part now. This may allow combine to merge this
+ with the store flag operation earlier into some sort of conditional
+ increment/decrement if the target allows it. */
+ if (common)
+ target = expand_simple_binop (mode, PLUS,
+ target, common,
+ target, 0, OPTAB_WIDEN);
+
/* Always use ifalse here. It should have been swapped with itrue
when appropriate when reversep is true. */
target = expand_simple_binop (mode, subtract_flag_p ? MINUS : PLUS,
gen_int_mode (ifalse, mode), target,
if_info->x, 0, OPTAB_WIDEN);
}
-
+ /* Other cases are not beneficial when the original A and B are PLUS
+ expressions. */
+ else if (common)
+ {
+ end_sequence ();
+ return FALSE;
+ }
/* if (test) x = 8; else x = 0;
=> x = (test != 0) << 3; */
else if (ifalse == 0 && (tmp = exact_log2 (itrue)) >= 0)
diff --git a/gcc/testsuite/gcc.target/aarch64/cinc_common_1.c b/gcc/testsuite/gcc.target/aarch64/cinc_common_1.c
new file mode 100644
index 0000000..d041263
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/cinc_common_1.c
@@ -0,0 +1,64 @@
+/* { dg-do run } */
+/* { dg-options "-save-temps -O2 -fno-inline" } */
+
+extern void abort (void);
+
+int
+foosi (int x)
+{
+ return x > 100 ? x - 2 : x - 1;
+}
+
+int
+barsi (int x)
+{
+ return x > 100 ? x + 4 : x + 3;
+}
+
+long
+foodi (long x)
+{
+ return x > 100 ? x - 2 : x - 1;
+}
+
+long
+bardi (long x)
+{
+ return x > 100 ? x + 4 : x + 3;
+}
+
+/* { dg-final { scan-assembler-times "cs?inc\tw\[0-9\]*" 2 } } */
+/* { dg-final { scan-assembler-times "cs?inc\tx\[0-9\]*" 2 } } */
+
+int
+main (void)
+{
+ if (foosi (105) != 103)
+ abort ();
+
+ if (foosi (95) != 94)
+ abort ();
+
+ if (barsi (105) != 109)
+ abort ();
+
+ if (barsi (95) != 98)
+ abort ();
+
+ if (foodi (105) != 103)
+ abort ();
+
+ if (foodi (95) != 94)
+ abort ();
+
+ if (bardi (105) != 109)
+ abort ();
+
+ if (bardi (95) != 98)
+ abort ();
+
+ return 0;
+}
+
+/* { dg-final { scan-assembler-not "csel\tx\[0-9\]*.*" } } */
+/* { dg-final { scan-assembler-not "csel\tw\[0-9\]*.*" } } */
