[llvm-commits] PATCH: Fix broken DAGCombiner which creates illegal vector shuffles

[Heikki Kultala]

 >> In current llvm-trunk there is a bug:
 >> If vector shuffles are not supported by the architecture but are 
marked to be
 >> expanded into extracts and builds, the dag legalization does this 
expand, but
 >> the dag combine which is done after the legalization converts these 
extracts and
 >> builds back to shuffles. This results an Cannot select error, 
compilelation fails.
 >>
 >> This patch adds a check which prevents this illegal combining if the
 >> architecture does not support shuffles.
 >
 > thanks for the patch, but unfortunately it causes this test to fail:
 >  CodeGen/X86/avx-zext.ll
 > At a guess, "VT" may not be the type actually used by the shuffle.
 >

It would seem "isOperationLegal()" does not consider custom-selected 
operations as legal.

Using isOperationLegalOrCustom() instead or isOperationLegal() seems to 
fix this.

Here is a fixed version of the patch attached
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