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Use char ops if possible for bit-field loads

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Set CF_FORCECHAR and change type to char once we have
shifted into a char.

This saves some unnecessary ldx #0 instructions.
This commit is contained in:
Jesse Rosenstock 2020-07-30 12:00:21 +02:00 committed by Oliver Schmidt
parent e38f601fcc
commit 2d5fd0fc63
2 changed files with 110 additions and 2 deletions
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20
src/cc65/loadexpr.c
View File

@ -193,10 +193,26 @@ void LoadExpr (unsigned Flags, struct ExprDesc* Expr)
** operations.
*/
if (ED_IsBitField (Expr)) {
unsigned F = CF_INT | CF_UNSIGNED | CF_CONST | (Flags & CF_TEST);
/* If the field was loaded as a char, force the shift/mask ops to be char ops.
** If it is a char, the load has already put 0 in the upper byte, so that can remain.
** CF_FORCECHAR does nothing if the type is not CF_CHAR.
*/
unsigned F = Flags | CF_FORCECHAR | CF_CONST;
/* Shift right by the bit offset */
g_asr (F, Expr->BitOffs);
/* And by the width if the field doesn't end on an int boundary */
/* Since we have now shifted down, we can do char ops as long as the width fits in
** a char.
*/
if (Expr->BitWidth <= CHAR_BITS) {
F |= CF_CHAR;
}
/* And by the width if the field doesn't end on a char or int boundary. If it does
** end on a boundary, then zeros have already been shifted in. g_and emits no code
** if the mask is all ones.
*/
if (Expr->BitOffs + Expr->BitWidth != CHAR_BITS &&
Expr->BitOffs + Expr->BitWidth != INT_BITS) {
g_and (F, (0x0001U << Expr->BitWidth) - 1U);

92
test/val/bitfield.c
View File

@ -182,12 +182,104 @@ static void test_overlap_with_int(void)
}
}
static struct full_width {
unsigned int x : 8;
unsigned int y : 16;
} fw = {255, 17};
static void test_full_width(void)
{
if (sizeof(struct full_width) != 3) {
printf("Got sizeof(struct full_width) = %zu, expected 3.\n",
sizeof(struct full_width));
failures++;
}
if (fw.x != 255) {
printf("Got fw.x = %u, expected 255.\n", fw.x);
failures++;
}
if (fw.y != 17) {
printf("Got fw.y = %u, expected 17.\n", fw.y);
failures++;
}
fw.x = 42;
fw.y = 1023;
if (fw.x != 42) {
printf("Got fw.x = %u, expected 42.\n", fw.x);
failures++;
}
if (fw.y != 1023) {
printf("Got fw.y = %u, expected 1023.\n", fw.y);
failures++;
}
}
static struct aligned_end {
unsigned int : 2;
unsigned int x : 6;
unsigned int : 3;
unsigned int y : 13;
/* z crosses a byte boundary, but fits in a byte when shifted. */
unsigned int : 6;
unsigned int z : 7;
} ae = {63, 17, 100};
static void test_aligned_end(void)
{
if (sizeof(struct aligned_end) != 5) {
printf("Got sizeof(struct aligned_end) = %zu, expected 5.\n",
sizeof(struct aligned_end));
failures++;
}
if (ae.x != 63) {
printf("Got ae.x = %u, expected 63.\n", ae.x);
failures++;
}
if (ae.y != 17) {
printf("Got ae.y = %u, expected 17.\n", ae.y);
failures++;
}
if (ae.z != 100) {
printf("Got ae.z = %u, expected 100.\n", ae.z);
failures++;
}
ae.x = 42;
ae.y = 1023;
ae.z = 66;
if (ae.x != 42) {
printf("Got ae.x = %u, expected 42.\n", ae.x);
failures++;
}
if (ae.y != 1023) {
printf("Got ae.y = %u, expected 1023.\n", ae.y);
failures++;
}
if (ae.z != 66) {
printf("Got ae.z = %u, expected 66.\n", ae.z);
failures++;
}
}
int main(void)
{
test_four_bits();
test_four_bits_with_int();
test_overlap();
test_overlap_with_int();
test_full_width();
test_aligned_end();
printf("failures: %u\n", failures);
return failures;
}