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emit_x64: Document ExtractMostSignificantBitFromPackedBytes

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MerryMage 2016-12-20 22:05:51 +00:00
parent 410e84434e
commit 03f168094d
1 changed files with 9 additions and 0 deletions
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9
src/backend_x64/emit_x64.cpp
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@ -1348,6 +1348,15 @@ void EmitX64::EmitSignedSaturatedSub(IR::Block& block, IR::Inst* inst) {
}
}
/**
* Extracts the most significant bits from each of the packed bytes, and packs them together.
*
* value before: a-------b-------c-------d-------
* value after: 0000000000000000000000000000abcd
*
* @param value The register containing the value to operate on. Result will be stored in the same register.
* @param a_tmp A register which can be used as a scratch register.
*/
static void ExtractMostSignificantBitFromPackedBytes(const Xbyak::util::Cpu& cpu_info, BlockOfCode* code, RegAlloc& reg_alloc, Xbyak::Reg32 value, boost::optional<Xbyak::Reg32> a_tmp = boost::none) {
if (cpu_info.has(Xbyak::util::Cpu::tBMI2)) {
Xbyak::Reg32 tmp = a_tmp ? *a_tmp : reg_alloc.ScratchGpr().cvt32();