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Fixed a bug that didn't preserve the accumulator's value when a simple 16-bit fetch-and-store is optimized. (#637)

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Fix a 16-bit fetch-and-store cc65 optimizer bug.
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greg-king5 2018-05-12 13:46:16 -04:00 • committed by GitHub
parent 2a78b9d3fe
commit ca31e3af1e
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2 changed files with 58 additions and 23 deletions
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45
src/cc65/coptstore.c
View file

@ -380,48 +380,48 @@ unsigned OptStore5 (CodeSeg* S)
** sta something
** stx something-else
**
** and replace it by
** and, replace it by
**
** lda foo
** sta something
** lda bar
** sta something-else
** lda foo
** sta something
**
** if X is not used later. This replacement doesn't save any cycles or bytes,
** but it keeps the value of X, which may be reused later.
** if the new value of X is not used later. That replacement doesn't save any
** cycles or bytes; but, it keeps the old value of X, which may be reused later.
*/
{
unsigned Changes = 0;
unsigned I = 0;
/* Walk over the entries */
unsigned I = 0;
while (I < CS_GetEntryCount (S)) {
CodeEntry* L[4];
/* Get next entry */
L[0] = CS_GetEntry (S, I);
/* Check for the sequence */
if (L[0]->OPC == OP65_LDA &&
!CS_RangeHasLabel (S, I+1, 3) &&
CS_GetEntries (S, L+1, I+1, 3) &&
L[1]->OPC == OP65_LDX &&
L[2]->OPC == OP65_STA &&
L[3]->OPC == OP65_STX &&
if (L[0]->OPC == OP65_LDA &&
!CS_RangeHasLabel (S, I+1, 3) &&
CS_GetEntries (S, L+1, I+1, 3) &&
L[1]->OPC == OP65_LDX &&
L[2]->OPC == OP65_STA &&
L[3]->OPC == OP65_STX &&
!RegXUsed (S, I+4)) {
CodeEntry* X;
CodeEntry* E = CS_GetEntry (S, I+1);
/* Insert the code after the sequence */
X = NewCodeEntry (OP65_LDA, L[1]->AM, L[1]->Arg, 0, L[1]->LI);
CS_InsertEntry (S, X, I+4);
X = NewCodeEntry (OP65_STA, L[3]->AM, L[3]->Arg, 0, L[3]->LI);
CS_InsertEntry (S, X, I+5);
/* Move the high-byte code to the beginning of the sequence */
CS_MoveEntry (S, I+1, I);
CS_MoveEntry (S, I+3, I+1);
/* Delete the old code */
CS_DelEntry (S, I+3);
CS_DelEntry (S, I+1);
/* Change from the X register to the A register */
CE_ReplaceOPC (E, OP65_LDA);
CE_ReplaceOPC (CS_GetEntry (S, I+1), OP65_STA);
/* Move labels from the old first entry to the new first entry */
CS_MoveLabels (S, CS_GetEntry (S, I+2), E);
/* Remember, we had changes */
++Changes;
@ -429,7 +429,6 @@ unsigned OptStore5 (CodeSeg* S)
/* Next entry */
++I;
}
/* Return the number of changes made */

36
test/val/assign-use1.c Normal file
View file

@ -0,0 +1,36 @@
/*
!!DESCRIPTION!! Assign an int; then, do an operation that depends directly on that assignment.
!!ORIGIN!! cc65 regression tests
!!LICENCE!! Public Domain
!!AUTHOR!! Greg King
*/
#include <stdio.h>
static unsigned char failures = 0;
static unsigned int result;
static const unsigned int buffer = 0xABCD;
int main(void)
{
result = buffer;
/* Shift doesn't use high byte (X register); previous assignment should be optimized. */
result <<= 8;
if (result != 0xCD00) {
++failures;
printf("assign-use1: left shift is $%X, not $CD00.\n", result);
}
result = buffer;
/* Shift does use high byte; previous assignment shouldn't be optimized by OptStore5(). */
result >>= 8;
if (result != 0x00AB) {
++failures;
printf("assign-use1: right shift is $%X, not $00AB.\n", result);
}
return failures;
}