[Bug target/113652] [14 regression] Failed bootstrap on ppc unrecognized opcode: `lfiwzx' with -mcpu=7450

["segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113652

--- Comment #20 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Michael Meissner from comment #19)
> When I wrote the VSX support many years ago, I intended that -mvsx enable
> all of ISA 2.06

But that is not how we do things, and it can never work predictably and
reliably.

If you want ISA 2.07 you have to use -mcpu=power8, or any other CPU that
implements that ISA level.  Using other options is counterintuitive, confusing,
and causes problems directly even.

> The reason is the kernel needs to
> be built without floating point support.

The kernel and many other things.  That's what -msoft-float, -mno-altivec, and
-mno-vsx are for.  Those options mean use no FPRs, no VRs, or no VSRs.  Nothing
more, nothing less.  

> If you say -mvsx, it should include the standard power7 integer instructions
> (-mpopcntd), power6 server instructions (i.e. -mhard-dfp, -mcmpb, -mrecip,
> -mpowerpc-gfxopt, and -mpowerpc-gpopt), etc.

No.  -mvsx means the compiler can use VSX things, is not prevented from it by
-mno-vsx.  There can be other reasons it can not use VSX, like, the targeted
CPU does not support VSX.

The option says absolutely nothing about any other instructions.

> VSX support assumes it can use lfiwax and lfiwzx.

Any CPU that supports VSX is ISA 2.07 at least, yes.