6502/cc65
1
0
Fork 0
mirror of https://github.com/cc65/cc65.git synced 2024-06-15 17:30:06 +00:00
Code Issues Projects Releases Wiki Activity

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

Browse Source 
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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

58
src/cc65/codegen.c
View File

@ -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);
}