https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65412
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
Target Milestone|--- |10.0
Last reconfirmed|2015-12-28 00:00:00 |2021-6-4
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
>From *.iftoswitch on the trunk:
;; Canonical GIMPLE case clusters: 0 1 2 3 4 5
So I looked and this is fixed but not for the low if count.
Take:
#define B(y) void f##y(void);
#define B10(y) B(y##0) B(y##1) B(y##2) \
B(y##3) B(y##4) B(y##5) \
B(y##6) B(y##7) B(y##8) \
B(y##9)
#define B100(y) B10(y##0) B10(y##1) B10(y##2) \
B10(y##3) B10(y##4) B10(y##5) \
B10(y##6) B10(y##7) B10(y##8) \
B10(y##9)
B10(1)
B100(1)
#define A(y) else if (x == y) f##y();
#define A10(y) A(y##0) \
A(y##1) \
A(y##2) \
A(y##3) \
A(y##4) \
A(y##5) \
A(y##6) \
A(y##7) \
A(y##8) \
A(y##9)
#define A100(y) A10(y##0) \
A10(y##1) \
A10(y##2) \
A10(y##3) \
A10(y##4) \
A10(y##5) \
A10(y##6) \
A10(y##7) \
A10(y##8) \
A10(y##9)
void f10(int x)
{
if (0) ;
A10(1)
}
void f100(int x)
{
if (0) ;
A100(1)
}
--- CUT ----
f100 is converted while f10 is not. This is a heuristics at work to see if it
is better as a jump table vs if statements.
https://godbolt.org/z/ofWGb5aKn for reference.
Clang decides (I don't know if they lower switches back to if statements) to do
the switch for all cases.
So we can close this as fixed.
