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tcg/optimize: With two const operands, prefer 0 in arg1

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For most binary operands, two const operands fold.
However, the add/sub carry opcodes have a third input.
Prefer "reg, zero, const" since many risc hosts have a
zero register that can fit a "reg, reg, const" insn format.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2025-01-14 23:08:24 -08:00
parent aeb3514bd0
commit e2f5ee36af
1 changed files with 12 additions and 6 deletions
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18
tcg/optimize.c
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@ -737,12 +737,18 @@ static int do_constant_folding_cond(TCGType type, TCGArg x,
#define NO_DEST temp_arg(NULL)
static int pref_commutative(TempOptInfo *ti)
{
/* Slight preference for non-zero constants second. */
return !ti_is_const(ti) ? 0 : ti_const_val(ti) ? 3 : 2;
}
static bool swap_commutative(TCGArg dest, TCGArg *p1, TCGArg *p2)
{
TCGArg a1 = *p1, a2 = *p2;
int sum = 0;
sum += arg_is_const(a1);
sum -= arg_is_const(a2);
sum += pref_commutative(arg_info(a1));
sum -= pref_commutative(arg_info(a2));
/* Prefer the constant in second argument, and then the form
op a, a, b, which is better handled on non-RISC hosts. */
@ -757,10 +763,10 @@ static bool swap_commutative(TCGArg dest, TCGArg *p1, TCGArg *p2)
static bool swap_commutative2(TCGArg *p1, TCGArg *p2)
{
int sum = 0;
sum += arg_is_const(p1[0]);
sum += arg_is_const(p1[1]);
sum -= arg_is_const(p2[0]);
sum -= arg_is_const(p2[1]);
sum += pref_commutative(arg_info(p1[0]));
sum += pref_commutative(arg_info(p1[1]));
sum -= pref_commutative(arg_info(p2[0]));
sum -= pref_commutative(arg_info(p2[1]));
if (sum > 0) {
TCGArg t;
t = p1[0], p1[0] = p2[0], p2[0] = t;