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Added support for changing multiplications with certain negative multipliers into bit-shifts. Only enable certain kinds of signed mul replacements with shift according to the code size factor settings.

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acqn 2020-07-02 10:30:02 +08:00 committed by Oliver Schmidt
parent ea7336591c
commit f59c2a08d9
1 changed files with 19 additions and 6 deletions
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25
src/cc65/codegen.c
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@ -2565,13 +2565,26 @@ void g_mul (unsigned flags, unsigned long val)
"tosmulax", "tosumulax", "tosmuleax", "tosumuleax"
};
int p2;
/* Do strength reduction if the value is constant and a power of two */
if (flags & CF_CONST && (p2 = PowerOf2 (val)) >= 0) {
/* Generate a shift instead */
g_asl (flags, p2);
return;
if (flags & CF_CONST) {
/* Deal with negative values if it's signed multiplication */
int Negation = (flags & CF_UNSIGNED) == 0 && (signed long)val < 0;
int p2 = PowerOf2 (Negation ? (unsigned long)-(signed long)val : val);
/* Check if we can use shift instead of multiplication */
if (p2 == 0 || (p2 > 0 && IS_Get (&CodeSizeFactor) >= (Negation ? 100 : 0))) {
/* Generate a shift instead */
g_asl (flags, p2);
/* Negate the result if val is negative */
if (Negation) {
g_neg (flags);
}
/* Done */
return;
}
}
/* If the right hand side is const, the lhs is not on stack but still