wiki:LongInteger

Version 1 (modified by cameron, 4 years ago) (diff)

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The LLVM Long Integer Project

This project involves the systematic support of the i128 and i256 integer types.

Ideally, we want two levels of support:

  • generic long integer support that works on any architecture supporting i64, and
  • support using efficient SIMD operations on 128-bit and 256-bit registers for architectures having such facilities.

The operations to be supported for these long integer types are all of the following, as documented in the LLVM IR reference manual:

  • add, sub
  • mul, udiv, sdiv
  • shl, lshr, ashr
  • and, or, xor
  • load, store
  • trunc, sext, zext
  • bitcast both bitcast-to long integer types and bitcast from.
  • icmp with the 10 different comparison types:
    • eq, ne
    • ugt, uge, ult, ule
    • sgt, sge, slt, sle
  • Byte swap intrinsics: @llvm.bswap.i128, @llvm.bswap.i256
  • Count intrinsics for population count, leading and trailing zeroes:
    • @llvm.popcount.i128, @llvm.popcount.i256
    • @llvm.ctlz.i128, @llvm.ctlz.i256
    • @llvm.cttz.i128, @llvm.cttz.i256
  • Overflow intrinsics
    • @llvm.sadd.with.overflow.i128, @llvm.sadd.with.overflow.i128 @llvm.uadd.with.overflow.i128, @llvm.uadd.with.overflow.i128
    • @llvm.ssub.with.overflow.i128, @llvm.ssub.with.overflow.i128 @llvm.usub.with.overflow.i128, @llvm.usub.with.overflow.i128
    • @llvm.smul.with.overflow.i128, @llvm.smul.with.overflow.i128 @llvm.umul.with.overflow.i128, @llvm.umul.with.overflow.i128

These types and operations may already be supported for some architectures. Investigate and document the support. Evaluate the code generation. Arrange to generate efficient SIMD implementations wherever possible.