[llvm-commits] Release-blocker-fix: PR13617 : LLVM+Clang emits movw instructionts with -march=armv6zk

[Stepan Dyatkovskiy]

Take #2.

I relaunched the thread. This bug is marked as release blocker... and 
the patch is pretty simple and it sitting for a few weeks without review 
:-( Please find it in attachment.

Some notes:

The bug is fired when dag-to-dag isel meets 'add' instruction with 
second operand that is negative number less than -256. E.g.:
add %var, -257

ARM dag-to-dag instruction selector matches the pattern that emits
(sub %var (MOVi16 Rd, 257))

After fast TableGen learning, I found that it ignores instruction 
predicates for patterns (ARMPat, ARMV6Pat and so on) while generating 
MatcherTable. So it ignores restrictions defined for MOVi16 instruction 
(ARMv6t2 and higher).

I also found that for several patterns this behaviour compensated in .td 
files by adding 'Requires' predicate explicitly. So, I did the same in 
this patch.

Thanks!

-Stepan.

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