[PATCH, PING] Fix common-code ppcf128 component access on little-endian

[Hal Finkel]

----- Original Message -----
> From: "Ulrich Weigand" <Ulrich.Weigand at de.ibm.com>
> To: "llvm-commits" <llvm-commits at cs.uiuc.edu>
> Sent: Monday, June 30, 2014 2:14:53 PM
> Subject: [PATCH,	PING] Fix common-code ppcf128 component access on little-endian
> 
> 
> 
> Hello,
> 
> the PowerPC 128-bit long double data type (ppcf128 in LLVM) is in
> fact a
> pair of two doubles, where one is considered the "high" or
> more-significant
> part, and the other is considered the "low" or less-significant part.
>  When
> a ppcf128 value is stored in memory or a register pair, the high part
> always comes first, i.e. at the lower memory address or in the
> lower-numbered register, and the low part always comes second.  This
> is
> true both on big-endian and little-endian PowerPC systems.  (Similar
> to how
> with a complex number, the real part always comes first and the
> imaginary
> part second, no matter the byte order of the system.)
> 
> This is currently implemented incorrectly for little-endian systems
> in
> LLVM.   There are three issues I've noticed in my tests on ppc64le:
> 
> - When printing an immediate ppcf128 constant to assembler output,
> current
> code in emitGlobalConstantFP does indeed correctly emit the high part
> first
> on big-endian systems, but emits the *low* part first on
> little-endian
> systems.
> - When lowering a ppcf128 type to a pair of f64 types in SelectionDAG
> (which is used e.g. when generating code to load an argument into a
> register pair), low and high part are inverted on little-endian
> systems.
> - In a related issue, because lowering ppcf128 into a pair of f64
> must
> operate differently from lowering an int128 into a pair of i64,
> bitcasts
> between ppcf128 and int128 must not be optimized away by the DAG
> combiner.
> 
> The attached patch fixes these issues; this makes all native testing
> on
> powerpc64le pass (including full test-suite and bootstrap), when my
> not-yet-published ELFv2 patches are also applied.
> 
> I'd appreciate a review; is this OK to commit?

The code itself looks fine, but with the exception of the printing code, is lacking regression tests. Please add regression tests to cover the other changes, and then commit.

Thanks again,
Hal

> 
> (See attached file: diff-llvm-le-ppcf128)
> 
> 
> Mit freundlichen Gruessen / Best Regards
> 
> Ulrich Weigand
> 
> --
>   Dr. Ulrich Weigand | Phone: +49-7031/16-3727
>   STSM, GNU/Linux compilers and toolchain
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-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory