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[X86][MC] no error diagnostic for out-of-range jrcxz/jecxz/jcxz

Authored by avl on Nov 15 2019, 10:48 AM.

Description

[X86][MC] no error diagnostic for out-of-range jrcxz/jecxz/jcxz

Fix for PR24072:

X86 instructions jrcxz/jecxz/jcxz performs short jumps if rcx/ecx/cx register is 0
The maximum relative offset for a forward short jump is 127 Bytes (0x7F).
The maximum relative offset for a backward short jump is 128 Bytes (0x80).

Gnu assembler warns when the distance of the jump exceeds the maximum but llvm-as does not.

Patch by Konstantin Belochapka and Alexey Lapshin

Differential Revision: https://reviews.llvm.org/D70652