[llvm] r319894 - [InstSimplify] Fold insertelement into undef if index is out of bounds

[Igor Laevsky via llvm-commits]

Hi Michael,

In the source code I see the following operations:
  %122 = extractelement <4 x i32> %121, i32 6
and:
  %124 = insertelement <4 x i32> %121, i32 %123, i32 6

This operations has undefined result (see https://llvm.org/docs/LangRef.html#extractelement-instruction). Looks like a bug in the frontend. Do you know what’s the best approach here?


On 12 Dec 2017, at 13:45, Michel Dänzer <michel at daenzer.net<mailto:michel at daenzer.net>> wrote:

On 2017-12-12 11:08 AM, Igor Laevsky wrote:
I reverted problematic changes in the https://reviews.llvm.org/rL320466

Thanks.


Is it possible to obtain an llvm-ir of the failing test case before the
optimizations? I can see the miscompile, but I can’t reproduce it using
optimised good case.

The attached should be the LLVM IR before optimizations.


--
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer
<fcc-read-to-pbo-after-clear.ll>

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