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Only enable signed div replacements with shift according to the code size factor settings.

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Also with better comments.
This commit is contained in:
acqn 2020-07-03 16:21:01 +08:00 committed by Oliver Schmidt
parent 09bcff0862
commit 85e73e91f8
1 changed files with 36 additions and 22 deletions

58
src/cc65/codegen.c

@ -2626,32 +2626,32 @@ void g_div (unsigned flags, unsigned long val)
"tosdivax", "tosudivax", "tosdiveax", "tosudiveax"
};
unsigned DoShiftLabel, EndLabel;
/* Deal with negative values as well as different sizes */
int Negation;
unsigned long NegatedVal;
unsigned MaskedVal;
/* Do strength reduction if the value is constant and a power of two */
int p2;
if (flags & CF_CONST) {
Negation = (flags & CF_UNSIGNED) == 0 && (signed long)val < 0;
NegatedVal = (unsigned long)-(signed long)val;
p2 = PowerOf2 (Negation ? NegatedVal : val);
if (p2 >= 0) {
/* Generate a shift instead */
if (flags & CF_UNSIGNED) {
g_asr (flags, p2);
return;
}
/* Deal with negative values as well as different sizes */
int Negation = (flags & CF_UNSIGNED) == 0 && (long)val < 0;
unsigned long NegatedVal = (unsigned long)-(long)val;
int p2 = PowerOf2 (Negation ? NegatedVal : val);
/* Generate a shift instead */
if ((flags & CF_UNSIGNED) != 0 && p2 > 0) {
g_asr (flags, p2);
return;
}
/* Check if we can afford using shift instead of multiplication at the
** cost of code size */
if (p2 == 0 || (p2 > 0 && IS_Get (&CodeSizeFactor) >= (Negation ? 200 : 170))) {
/* Generate a conditional shift instead */
if (p2 > 0) {
/* GitHub #169 - if abs(expr) < abs(val), the result is always 0 */
DoShiftLabel = GetLocalLabel ();
EndLabel = GetLocalLabel ();
MaskedVal = Negation ? val : NegatedVal;
unsigned int DoShiftLabel = GetLocalLabel ();
unsigned int EndLabel = GetLocalLabel ();
unsigned long MaskedVal = Negation ? val : NegatedVal;
/* GitHub #169 - if abs(expr) < abs(val), the result is always 0.
** First, check whether expr >= 0 and skip to the shift if true.
*/
switch (flags & CF_TYPEMASK) {
case CF_CHAR:
if (flags & CF_FORCECHAR) {
@ -2678,19 +2678,33 @@ void g_div (unsigned flags, unsigned long val)
typeerror (flags);
break;
}
/* Second, check whether expr <= -asb(val) and skip to the
** shift if true. The original content of expr has to be saved
** before the checking comparison and restored after that, as
** the content in Primary register will be destroyed.
** The result of the comparison is a boolean. We can store
** it in the Carry flag with a LSR and branch on it later.
*/
g_save (flags);
g_le (flags | CF_UNSIGNED, MaskedVal);
AddCodeLine ("lsr a");
g_restore (flags);
AddCodeLine ("bcs %s", LocalLabelName (DoShiftLabel));
/* The result is 0. We can just load 0 and skip the shifting. */
g_getimmed (flags | CF_ABSOLUTE, 0, 0);
g_jump (EndLabel);
/* Do the shift. The sign of the result may need be corrected
** later.
*/
g_defcodelabel (DoShiftLabel);
g_asr (flags, p2);
g_defcodelabel (EndLabel);
}
/* Negate the result if val is negative */
/* Negate the result as long as val < 0, even if val == -1 and no
** shift was generated. */
if (Negation) {
g_neg (flags);
}