[X86][AsmParser] Ignore "short" even harder in Intel syntax ASM.

Authored by dlj on May 16 2019, 4:27 PM.

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[X86][AsmParser] Ignore "short" even harder in Intel syntax ASM.

In Intel syntax, it's not uncommon to see a "short" modifier on Jcc conditional
jumps, which indicates the offset should be a "short jump" (8-bit immediate
offset from EIP, -128 to +127). This patch expands to all recognized Jcc
condition codes, and removes the inline restriction.

Clang already ignores "jmp short" in inline assembly. However, only "jmp" and a
couple of Jcc are actually checked, and only inline (i.e., not when using the
integrated assembler for asm sources). A quick search through asm-containing
libraries at hand shows a pretty broad range of Jcc conditions spelled with

GAS ignores the "short" modifier, and instead uses an encoding based on the
given immediate. MS inline seems to do the same, and I suspect MASM does, too.
NASM will yield an error if presented with an out-of-range immediate value.

Example of GCC 9.1 and MSVC v19.20, "jmp short" with offsets that do and do not
fit within 8 bits: https://gcc.godbolt.org/z/aFZmjY

Differential Revision: https://reviews.llvm.org/D61990

llvm-svn: 360954


sidorovdMay 24 2019, 5:43 AM
Differential Revision
D61990: [X86] Ignore "short" even harder in Intel ASM.

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