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Remove more push/pop sequences.

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git-svn-id: svn://svn.cc65.org/cc65/trunk@4010 b7a2c559-68d2-44c3-8de9-860c34a00d81
This commit is contained in:
uz 2009-08-15 10:27:41 +00:00
parent d27664036d
commit b68db83a2b
1 changed files with 72 additions and 8 deletions
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80
src/cc65/coptind.c
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@ -51,6 +51,39 @@
static int MemAccess (CodeSeg* S, unsigned From, unsigned To, const char* Arg)
/* Checks a range of code entries if there are any memory accesses to Arg.
* Note: This function is not 100% safe, because there is more than one way
* to express a memory location ("foo" and "foo+0" comes to mind) and there
* may be other accesses through pointers. For the code generated by cc65 and
* for the purpose of the caller (OptPushPop) it is assumed to be safe enough
* however.
*/
{
/* Walk over all code entries */
while (From <= To) {
/* Get the next entry */
CodeEntry* E = CS_GetEntry (S, From);
/* For simplicity, we just check if there is an argument and if this
* argument equals Arg.
*/
if (E->Arg && strcmp (E->Arg, Arg) == 0) {
/* Found an access */
return 1;
}
/* Next entry */
++From;
}
/* Nothing found */
return 0;
}
static int GetBranchDist (CodeSeg* S, unsigned From, CodeEntry* To)
/* Get the branch distance between the two entries and return it. The distance
* will be negative for backward jumps and positive for forward jumps.
@ -1225,6 +1258,8 @@ unsigned OptPushPop (CodeSeg* S)
unsigned I = 0;
while (I < CS_GetEntryCount (S)) {
CodeEntry* X;
/* Get next entry */
CodeEntry* E = CS_GetEntry (S, I);
@ -1245,19 +1280,47 @@ unsigned OptPushPop (CodeSeg* S)
} else if (E->OPC == OP65_PLA) {
/* Found a matching pop */
Pop = I;
State = FoundPop;
/* Check that the block between Push and Pop is a basic
* block (one entry, one exit). Otherwise ignore it.
*/
if (CS_IsBasicBlock (S, Push, Pop)) {
State = FoundPop;
} else {
/* Go into searching mode again */
State = Searching;
}
}
break;
case FoundPop:
/* Next insn, just check if it is no conditional branch and
* that A is not used later. Check also that the range we have
* found now is a basic block, which means that the PHA is the
* only entrance and the PLA the only exit.
/* We're at the instruction after the PLA.
* Check for the following conditions:
* - If this instruction is a store of A, and A is not used
* later, we may replace the PHA by the store and remove
* pla if several other conditions are met.
* - If this instruction is not a conditional branch, and A
* is unused later, we may remove PHA and PLA.
*/
if ((E->Info & OF_CBRA) == 0 &&
!RegAUsed (S, I) &&
CS_IsBasicBlock (S, Push, Pop)) {
if (E->OPC == OP65_STA &&
!RegAUsed (S, I+1) &&
!MemAccess (S, Push+1, Pop-1, E->Arg)) {
/* Insert a STA before the PHA */
X = NewCodeEntry (E->OPC, E->AM, E->Arg, E->JumpTo, E->LI);
CS_InsertEntry (S, X, Push);
/* Remove the PHA instead */
CS_DelEntry (S, Push+1);
/* Remove the PLA/STA sequence */
CS_DelEntries (S, Pop, 2);
/* Remember we had changes */
++Changes;
} else if ((E->Info & OF_CBRA) == 0 &&
!RegAUsed (S, I)) {
/* We can remove the PHA and PLA instructions */
CS_DelEntry (S, Pop);
CS_DelEntry (S, Push);
@ -1265,6 +1328,7 @@ unsigned OptPushPop (CodeSeg* S)
I -= 2;
/* Remember we had changes */
++Changes;
}
/* Go into search mode again */
State = Searching;