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AMDGPU: Add comment for VOP2b operand class

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Because of the constant bus requirement, it is never legal to
use a literal constant for these instructions despite the encoding
allowing it. This was already doing the right thing, but note why.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249500 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Matt Arsenault 2015-10-07 01:36:00 +00:00
parent bb32f88e5d
commit 3eab2d1f26
1 changed files with 5 additions and 0 deletions
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5
lib/Target/AMDGPU/SIInstrInfo.td
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@ -1187,6 +1187,11 @@ def VOP2b_I32_I1_I32_I32 : VOPProfile<[i32, i32, i32, untyped]> {
// Write out to vcc or arbitrary SGPR and read in from vcc or
// arbitrary SGPR.
def VOP2b_I32_I1_I32_I32_I1 : VOPProfile<[i32, i32, i32, i1]> {
// We use VCSrc_32 to exclude literal constants, even though the
// encoding normally allows them since the implicit VCC use means
// using one would always violate the constant bus
// restriction. SGPRs are still allowed because it should
// technically be possible to use VCC again as src0.
let Src0RC32 = VCSrc_32;
let Asm32 = "$dst, vcc, $src0, $src1, vcc";
let Asm64 = "$dst, $sdst, $src0, $src1, $src2";