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are more specific version of the comparison removal #895

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bbbradsmith 2019-05-24 23:51:22 -04:00 committed by Oliver Schmidt
parent 7a863e5cda
commit 4642421da4
1 changed files with 20 additions and 10 deletions
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30
src/cc65/coptcmp.c
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@ -819,6 +819,7 @@ unsigned OptCmp8 (CodeSeg* S)
/* We are able to evaluate the compare at compile time. Check if
** one or more branches are ahead.
*/
unsigned ProtectCompare = 0;
unsigned JumpsChanged = 0;
CodeEntry* N;
while ((N = CS_GetNextEntry (S, I)) != 0 && /* Followed by something.. */
@ -878,6 +879,21 @@ unsigned OptCmp8 (CodeSeg* S)
CodeEntry* X = NewCodeEntry (OP65_JMP, AM65_BRA, LabelName, L, N->LI);
CS_InsertEntry (S, X, I+2);
CS_DelEntry (S, I+1);
/* Normally we can remove the compare as well,
** but some comparisons generate code with a
** shared branch operation. This prevents the unsafe
** removal of the compare for known problem cases.
*/
if (
/* Jump to branch that relies on the comparison. */
(L->Owner->Info & (OF_CBRA | OF_ZBRA)) ||
/* Jump to boolean transformer that relies on the comparison. */
(L->Owner->OPC == OP65_JSR &&
(FindBoolCmpCond (L->Owner->Arg)) != CMP_INV)
)
{
++ProtectCompare;
}
}
/* Remember, we had changes */
@ -885,16 +901,10 @@ unsigned OptCmp8 (CodeSeg* S)
++Changes;
}
/* "If we have made changes above, we may also remove the compare."
**
** Removing the compare was too aggressive. E.g. for 16-bit compares the compiler
** may generate a branch to a second shared branch that still requires the flag
** result of the first compare instruction.
**
**if (JumpsChanged) {
** CS_DelEntry (S, I);
**}
*/
/* Delete the original compare, if safe to do so. */
if (JumpsChanged && !ProtectCompare) {
CS_DelEntry (S, I);
}
}
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