[Bug tree-optimization/65412] sequence of ifs not turned into a switch statement

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65412

--- Comment #4 from Andrew Pinski  ---
clang decides at 4 to change it to a switch statement while GCC takes a few
extra ifs to change it.  Again this is heuristics at work.


#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)

B10(1)

#define A(y) else if (x == y) f##y();

void f10(int x)
{
  if (0) ;
  A(11)
  A(12)
  A(13)
  A(14)
}

[Bug tree-optimization/65412] sequence of ifs not turned into a switch statement

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65412

Andrew Pinski  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  ---
>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.