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opt: Start optimizing dead code a bit

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If a condition is always zero/non-zero we can omit the
then or else code.  This is complicated a bit by having to
deal with labels that might make such code reachable without
us yet knowing during parsing.
This commit is contained in:
Michael Matz
2016-09-19 18:38:12 +02:00
parent b303a00ce0
commit 31c7ea0165
4 changed files with 182 additions and 2 deletions
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27
tests/tcctest.c
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@ -88,6 +88,7 @@ void struct_test();
void array_test();
void expr_ptr_test();
void bool_test();
void optimize_out();
void expr2_test();
void constant_expr_test();
void expr_cmp_test();
@ -695,6 +696,7 @@ int main(int argc, char **argv)
array_test();
expr_ptr_test();
bool_test();
optimize_out();
expr2_test();
constant_expr_test();
expr_cmp_test();
@ -1165,6 +1167,31 @@ void bool_test()
printf ("bits = 0x%x\n", calc_vm_flags (0x1));
}
extern int undefined_function(void);
extern int defined_function(void);
void optimize_out(void)
{
int i = 0 ? undefined_function() : defined_function();
printf ("oo:%d\n", i);
int j = 1 ? defined_function() : undefined_function();
printf ("oo:%d\n", j);
if (0)
printf("oo:%d\n", undefined_function());
else
printf("oo:%d\n", defined_function());
if (1)
printf("oo:%d\n", defined_function());
else
printf("oo:%d\n", undefined_function());
}
int defined_function(void)
{
static int i = 40;
return i++;
}
/* GCC accepts that */
static int tab_reinit[];
static int tab_reinit[10];