[Bug target/91400] __builtin_cpu_supports conjunction is optimized poorly

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91400

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Target|                            |x86_64-*-*, i?86-*-*
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2019-08-09
          Component|tree-optimization           |target
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  The issue is that the target builds a new(!) VAR_DECL for
__cpu_mode for _each_(!) invocation of __builtin_cpu_supports so the GIMPLE
level optimizers have no chance to CSE the loads.  The two VAR_DECLs for
this testcase are

<var_decl 0x7ffff7fefb40 __cpu_model type <record_type 0x7ffff69c8888
__processor_model>
            public static external weak preserve BLK (null):0:0
            size <integer_cst 0x7ffff69ade10 constant 160>
            unit-size <integer_cst 0x7ffff69ade40 constant 20>
            align:32 warn_if_not_align:0>

<var_decl 0x7ffff7fefab0 __cpu_model type <record_type 0x7ffff69c8498
__processor_model>
            public static external weak preserve BLK (null):0:0
            size <integer_cst 0x7ffff69ade10 constant 160>
            unit-size <integer_cst 0x7ffff69ade40 constant 20>
            align:32 warn_if_not_align:0>

so you can see that we even re-build the RECORD_TYPE from scratch... :/