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shader: Fold integer FMA from Nvidia's pattern 

Fold shaders doing "a * b + c" on integers from the pattern generated by
Nvidia's GL compiler.

On a somewhat complex compute shader it reduces the code size by 16
instructions from 2 matches on Turing GPUs.

On Intel as extracted from KHR_pipeline_executable_properties:
Before the optimization:
```
Instruction Count: 2057
Basic Block Count: 45
Scratch Memory Size: 14752
Spill Count: 232
Fill Count: 261
SEND Count: 610
Cycle Count: 11325
```

After the optimization:
```
Instruction Count: 2046
Basic Block Count: 44
Scratch Memory Size: 13728
Spill Count: 219
Fill Count: 268
SEND Count: 604
Cycle Count: 11367
```
This commit is contained in:
ReinUsesLisp 2021-07-26 04:24:26 -03:00
parent 09fb41dc63
commit 66a0cedba3
1 changed files with 175 additions and 0 deletions
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175
src/shader_recompiler/ir_opt/constant_propagation_pass.cpp
View File

@ -3,6 +3,7 @@
// Refer to the license.txt file included.
#include <algorithm>
#include <functional>
#include <tuple>
#include <type_traits>
@ -88,6 +89,26 @@ bool FoldWhenAllImmediates(IR::Inst& inst, Func&& func) {
return true;
}
/// Return true when all values in a range are equal
template <typename Range>
bool AreEqual(const Range& range) {
auto resolver{[](const auto& value) { return value.Resolve(); }};
auto equal{[](const IR::Value& lhs, const IR::Value& rhs) {
if (lhs == rhs) {
return true;
}
// Not equal, but try to match if they read the same constant buffer
if (!lhs.IsImmediate() && !rhs.IsImmediate() &&
lhs.Inst()->GetOpcode() == IR::Opcode::GetCbufU32 &&
rhs.Inst()->GetOpcode() == IR::Opcode::GetCbufU32 &&
lhs.Inst()->Arg(0) == rhs.Inst()->Arg(0) && lhs.Inst()->Arg(1) == rhs.Inst()->Arg(1)) {
return true;
}
return false;
}};
return std::ranges::adjacent_find(range, std::not_fn(equal), resolver) == std::end(range);
}
void FoldGetRegister(IR::Inst& inst) {
if (inst.Arg(0).Reg() == IR::Reg::RZ) {
inst.ReplaceUsesWith(IR::Value{u32{0}});
@ -100,6 +121,157 @@ void FoldGetPred(IR::Inst& inst) {
}
}
/// Replaces the XMAD pattern generated by an integer FMA
bool FoldXmadMultiplyAdd(IR::Block& block, IR::Inst& inst) {
/*
* We are looking for this specific pattern:
* %6 = BitFieldUExtract %op_b, #0, #16
* %7 = BitFieldUExtract %op_a', #16, #16
* %8 = IMul32 %6, %7
* %10 = BitFieldUExtract %op_a', #0, #16
* %11 = BitFieldInsert %8, %10, #16, #16
* %15 = BitFieldUExtract %op_b, #0, #16
* %16 = BitFieldUExtract %op_a, #0, #16
* %17 = IMul32 %15, %16
* %18 = IAdd32 %17, %op_c
* %22 = BitFieldUExtract %op_b, #16, #16
* %23 = BitFieldUExtract %11, #16, #16
* %24 = IMul32 %22, %23
* %25 = ShiftLeftLogical32 %24, #16
* %26 = ShiftLeftLogical32 %11, #16
* %27 = IAdd32 %26, %18
* %result = IAdd32 %25, %27
*
* And replace it with:
* %temp = IMul32 %op_a, %op_b
* %result = IAdd32 %temp, %op_c
*
* This optimization has been proven safe by Nvidia's compiler logic being reversed.
* (If Nvidia generates this code from 'fma(a, b, c)', we can do the same in the reverse order.)
*/
const IR::Value zero{0u};
const IR::Value sixteen{16u};
IR::Inst* const _25{inst.Arg(0).TryInstRecursive()};
IR::Inst* const _27{inst.Arg(1).TryInstRecursive()};
if (!_25 || !_27) {
return false;
}
if (_27->GetOpcode() != IR::Opcode::IAdd32) {
return false;
}
if (_25->GetOpcode() != IR::Opcode::ShiftLeftLogical32 || _25->Arg(1) != sixteen) {
return false;
}
IR::Inst* const _24{_25->Arg(0).TryInstRecursive()};
if (!_24 || _24->GetOpcode() != IR::Opcode::IMul32) {
return false;
}
IR::Inst* const _22{_24->Arg(0).TryInstRecursive()};
IR::Inst* const _23{_24->Arg(1).TryInstRecursive()};
if (!_22 || !_23) {
return false;
}
if (_22->GetOpcode() != IR::Opcode::BitFieldUExtract) {
return false;
}
if (_23->GetOpcode() != IR::Opcode::BitFieldUExtract) {
return false;
}
if (_22->Arg(1) != sixteen || _22->Arg(2) != sixteen) {
return false;
}
if (_23->Arg(1) != sixteen || _23->Arg(2) != sixteen) {
return false;
}
IR::Inst* const _11{_23->Arg(0).TryInstRecursive()};
if (!_11 || _11->GetOpcode() != IR::Opcode::BitFieldInsert) {
return false;
}
if (_11->Arg(2) != sixteen || _11->Arg(3) != sixteen) {
return false;
}
IR::Inst* const _8{_11->Arg(0).TryInstRecursive()};
IR::Inst* const _10{_11->Arg(1).TryInstRecursive()};
if (!_8 || !_10) {
return false;
}
if (_8->GetOpcode() != IR::Opcode::IMul32) {
return false;
}
if (_10->GetOpcode() != IR::Opcode::BitFieldUExtract) {
return false;
}
IR::Inst* const _6{_8->Arg(0).TryInstRecursive()};
IR::Inst* const _7{_8->Arg(1).TryInstRecursive()};
if (!_6 || !_7) {
return false;
}
if (_6->GetOpcode() != IR::Opcode::BitFieldUExtract) {
return false;
}
if (_7->GetOpcode() != IR::Opcode::BitFieldUExtract) {
return false;
}
if (_6->Arg(1) != zero || _6->Arg(2) != sixteen) {
return false;
}
if (_7->Arg(1) != sixteen || _7->Arg(2) != sixteen) {
return false;
}
IR::Inst* const _26{_27->Arg(0).TryInstRecursive()};
IR::Inst* const _18{_27->Arg(1).TryInstRecursive()};
if (!_26 || !_18) {
return false;
}
if (_26->GetOpcode() != IR::Opcode::ShiftLeftLogical32 || _26->Arg(1) != sixteen) {
return false;
}
if (_26->Arg(0).InstRecursive() != _11) {
return false;
}
if (_18->GetOpcode() != IR::Opcode::IAdd32) {
return false;
}
IR::Inst* const _17{_18->Arg(0).TryInstRecursive()};
if (!_17 || _17->GetOpcode() != IR::Opcode::IMul32) {
return false;
}
IR::Inst* const _15{_17->Arg(0).TryInstRecursive()};
IR::Inst* const _16{_17->Arg(1).TryInstRecursive()};
if (!_15 || !_16) {
return false;
}
if (_15->GetOpcode() != IR::Opcode::BitFieldUExtract) {
return false;
}
if (_16->GetOpcode() != IR::Opcode::BitFieldUExtract) {
return false;
}
if (_15->Arg(1) != zero || _16->Arg(1) != zero || _10->Arg(1) != zero) {
return false;
}
if (_15->Arg(2) != sixteen || _16->Arg(2) != sixteen || _10->Arg(2) != sixteen) {
return false;
}
const std::array<IR::Value, 3> op_as{
_7->Arg(0).Resolve(),
_16->Arg(0).Resolve(),
_10->Arg(0).Resolve(),
};
const std::array<IR::Value, 3> op_bs{
_22->Arg(0).Resolve(),
_6->Arg(0).Resolve(),
_15->Arg(0).Resolve(),
};
const IR::U32 op_c{_18->Arg(1)};
if (!AreEqual(op_as) || !AreEqual(op_bs)) {
return false;
}
IR::IREmitter ir{block, IR::Block::InstructionList::s_iterator_to(inst)};
inst.ReplaceUsesWith(ir.IAdd(ir.IMul(IR::U32{op_as[0]}, IR::U32{op_bs[1]}), op_c));
return true;
}
/// Replaces the pattern generated by two XMAD multiplications
bool FoldXmadMultiply(IR::Block& block, IR::Inst& inst) {
/*
@ -179,6 +351,9 @@ void FoldAdd(IR::Block& block, IR::Inst& inst) {
if (FoldXmadMultiply(block, inst)) {
return;
}
if (FoldXmadMultiplyAdd(block, inst)) {
return;
}
}
}