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aco: use s_waitcnt_depctr to mitigate VMEMtoScalarWriteHazard

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Apparently this is potentially faster than v_nop:
https://reviews.llvm.org/D83872

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5923>
This commit is contained in:
Rhys Perry
2020-07-15 17:08:01 +01:00
committed by Marge Bot
parent bcf94bb933
commit f302ef3853
1 changed files with 10 additions and 3 deletions
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src/amd/compiler/aco_insert_NOPs.cpp
+10 -3
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@@ -608,15 +608,22 @@ void handle_instruction_gfx10(Program *program, Block *cur_block, NOP_ctx_gfx10
unsigned vmcnt = (imm & 0xF) | ((imm & (0x3 << 14)) >> 10);
if (vmcnt == 0)
ctx.sgprs_read_by_VMEM.reset();
} else if (instr->opcode == aco_opcode::s_waitcnt_depctr) {
/* Hazard is mitigated by a s_waitcnt_depctr with a magic imm */
const SOPP_instruction *sopp = static_cast<const SOPP_instruction *>(instr.get());
if (sopp->imm == 0xffe3)
ctx.sgprs_read_by_VMEM.reset();
}
/* Check if SALU writes an SGPR that was previously read by the VALU */
if (check_written_regs(instr, ctx.sgprs_read_by_VMEM)) {
ctx.sgprs_read_by_VMEM.reset();
/* Insert v_nop to mitigate the problem */
aco_ptr<VOP1_instruction> nop{create_instruction<VOP1_instruction>(aco_opcode::v_nop, Format::VOP1, 0, 0)};
new_instructions.emplace_back(std::move(nop));
/* Insert s_waitcnt_depctr instruction with magic imm to mitigate the problem */
aco_ptr<SOPP_instruction> depctr{create_instruction<SOPP_instruction>(aco_opcode::s_waitcnt_depctr, Format::SOPP, 0, 0)};
depctr->imm = 0xffe3;
depctr->block = -1;
new_instructions.emplace_back(std::move(depctr));
}
} else if (instr->isVALU()) {
/* Hazard is mitigated by any VALU instruction */