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Use u16 codegen for u8 x u8 ops

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In g_typeadjust, before we apply the integral promotions, we check if
both types are unsigned char.  If so, we promote to unsigned int, rather
than int, which would be chosen by the standard rules.  This is only a
performance optimization and does not affect correctness, as the flags
returned by g_typeadjust are only used for code generation, and not to
determine types of other expressions containing this one.  All unsigned
char bit-patterns are valid as both int and unsigned int and represent
the same value, so either signed or unsigned int operations can be used.
This special case part is not duplicated by ArithmeticConvert.

Partial fix for #1308.
This commit is contained in:
Jesse Rosenstock 2020-10-28 08:13:30 +01:00 committed by Oliver Schmidt
parent 81edc3f582
commit 5db74b4b19
2 changed files with 21 additions and 3 deletions
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13
src/cc65/codegen.c
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@ -1432,6 +1432,19 @@ unsigned g_typeadjust (unsigned lhs, unsigned rhs)
/* Note that this logic is largely duplicated by ArithmeticConvert. */
/* Before we apply the integral promotions, we check if both types are unsigned char.
** If so, we return unsigned int, rather than int, which would be returned by the standard
** rules. This is only a performance optimization and does not affect correctness, as
** the flags are only used for code generation, and not to determine types of other
** expressions containing this one. All unsigned char bit-patterns are valid as both int
** and unsigned int and represent the same value, so either signed or unsigned int operations
** can be used. This special case part is not duplicated by ArithmeticConvert.
*/
if ((lhs & CF_TYPEMASK) == CF_CHAR && (lhs & CF_UNSIGNED) &&
(rhs & CF_TYPEMASK) == CF_CHAR && (rhs & CF_UNSIGNED)) {
return const_flag | CF_UNSIGNED | CF_INT;
}
/* Apply integral promotions for types char/short. */
lhs = g_intpromotion (lhs);
rhs = g_intpromotion (rhs);

11
test/val/char-promote.c
View File

@ -68,7 +68,8 @@ void test_mul (void)
#endif
/* The unsigned chars get promoted to int, so this is -511.
** We should also be able to observe that the generated code uses mul, not umul.
** We should also be able to observe that, due to optimizations from #1315, the generated code
** uses umul, not mul.
*/
if (two_fifty_five * two_fifty_five != -511) {
fprintf (stderr, "Expected two_fifty_five * two_fifty_five == -511\n");
@ -89,7 +90,9 @@ void test_div (void)
const u8 seventeen = 17;
const u8 three = 3;
/* We should also be able to observe that the generated code uses div, not udiv. */
/* We should also be able to observe that, due to optimizations from #1315, the generated code
** uses udiv, not div.
*/
if (seventeen / three != 5) {
fprintf (stderr, "Expected seventeen / three == 5, got: %d\n", seventeen / three);
failures++;
@ -105,7 +108,9 @@ void test_shr (void)
const unsigned int forty_two = 42;
const unsigned int two = 2;
/* We should also be able to observe that the generated code uses asr, not shr. */
/* We should also be able to observe that, due to optimizations from #1315, the generated code
** uses shr, not asr.
*/
if (forty_two >> two != 10) {
fprintf (stderr, "Expected forty_two / two == 10, got: %d\n", forty_two >> two);
failures++;