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[AMDGPU][CodeGen] To improve CGEMM performance: combine LDS reads. 

hange explores the fact that LDS reads may be reordered even if access
the same location.

Prior the change, algorithm immediately stops as soon as any memory
access encountered between loads that are expected to be merged
together. Although, Read-After-Read conflict cannot affect execution
correctness.

Improves hcBLAS CGEMM manually loop-unrolled kernels performance by 44%.
Also improvement expected on any massive sequences of reads from LDS.

Differential Revision: https://reviews.llvm.org/D25944

llvm-svn: 285919
This commit is contained in:
Alexander Timofeev 2016-11-03 14:37:13 +00:00
parent 73aba6229f
commit f867a40bf6
2 changed files with 59 additions and 5 deletions
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24
llvm/lib/Target/AMDGPU/SILoadStoreOptimizer.cpp
View File

@ -141,6 +141,18 @@ static void addDefsToList(const MachineInstr &MI,
}
}
static bool memAccessesCanBeReordered(
MachineBasicBlock::iterator A,
MachineBasicBlock::iterator B,
const SIInstrInfo *TII,
llvm::AliasAnalysis * AA) {
return (TII->areMemAccessesTriviallyDisjoint(*A, *B, AA) ||
// RAW or WAR - cannot reorder
// WAW - cannot reorder
// RAR - safe to reorder
!(A->mayStore() || B->mayStore()));
}
// Add MI and its defs to the lists if MI reads one of the defs that are
// already in the list. Returns true in that case.
static bool
@ -173,8 +185,8 @@ canMoveInstsAcrossMemOp(MachineInstr &MemOp,
for (MachineInstr *InstToMove : InstsToMove) {
if (!InstToMove->mayLoadOrStore())
continue;
if (!TII->areMemAccessesTriviallyDisjoint(MemOp, *InstToMove, AA))
return false;
if (!memAccessesCanBeReordered(MemOp, *InstToMove, TII, AA))
return false;
}
return true;
}
@ -233,7 +245,7 @@ SILoadStoreOptimizer::findMatchingDSInst(MachineBasicBlock::iterator I,
return E;
if (MBBI->mayLoadOrStore() &&
!TII->areMemAccessesTriviallyDisjoint(*I, *MBBI, AA)) {
!memAccessesCanBeReordered(*I, *MBBI, TII, AA)) {
// We fail condition #1, but we may still be able to satisfy condition
// #2. Add this instruction to the move list and then we will check
// if condition #2 holds once we have selected the matching instruction.
@ -288,8 +300,10 @@ SILoadStoreOptimizer::findMatchingDSInst(MachineBasicBlock::iterator I,
// We could potentially keep looking, but we'd need to make sure that
// it was safe to move I and also all the instruction in InstsToMove
// down past this instruction.
// FIXME: This is too conservative.
break;
if (!memAccessesCanBeReordered(*I, *MBBI, TII, AA) || // check if we can move I across MBBI
!canMoveInstsAcrossMemOp(*MBBI, InstsToMove, TII, AA) // check if we can move all I's users
)
break;
}
return E;
}

40
llvm/test/CodeGen/AMDGPU/ds_read2.ll
View File

@ -493,6 +493,46 @@ define void @misaligned_read2_i64(i64 addrspace(1)* %out, i64 addrspace(3)* %in)
ret void
}
; SI-LABEL: ds_read_diff_base_interleaving
; SI-NOT: ds_read_b32
define amdgpu_kernel void @ds_read_diff_base_interleaving(
float addrspace(1)* nocapture %arg,
[4 x [4 x float]] addrspace(3)* %arg1,
[4 x [4 x float]] addrspace(3)* %arg2,
[4 x [4 x float]] addrspace(3)* %arg3,
[4 x [4 x float]] addrspace(3)* %arg4) #1 {
bb:
%tmp = getelementptr float, float addrspace(1)* %arg, i64 10
%tmp5 = tail call i32 @llvm.amdgcn.workitem.id.x() #2
%tmp6 = tail call i32 @llvm.amdgcn.workitem.id.y() #2
%tmp7 = getelementptr [4 x [4 x float]], [4 x [4 x float]] addrspace(3)* %arg1, i32 0, i32 %tmp6, i32 0
%tmp8 = getelementptr [4 x [4 x float]], [4 x [4 x float]] addrspace(3)* %arg2, i32 0, i32 0, i32 %tmp5
%tmp9 = getelementptr [4 x [4 x float]], [4 x [4 x float]] addrspace(3)* %arg3, i32 0, i32 %tmp6, i32 0
%tmp10 = getelementptr [4 x [4 x float]], [4 x [4 x float]] addrspace(3)* %arg4, i32 0, i32 0, i32 %tmp5
%tmp11 = getelementptr [4 x [4 x float]], [4 x [4 x float]] addrspace(3)* %arg1, i32 0, i32 %tmp6, i32 1
%tmp12 = getelementptr [4 x [4 x float]], [4 x [4 x float]] addrspace(3)* %arg2, i32 0, i32 1, i32 %tmp5
%tmp13 = getelementptr [4 x [4 x float]], [4 x [4 x float]] addrspace(3)* %arg3, i32 0, i32 %tmp6, i32 1
%tmp14 = getelementptr [4 x [4 x float]], [4 x [4 x float]] addrspace(3)* %arg4, i32 0, i32 1, i32 %tmp5
%tmp15 = load float, float addrspace(3)* %tmp7
%tmp16 = load float, float addrspace(3)* %tmp8
%tmp17 = fmul float %tmp15, %tmp16
%tmp18 = fadd float 2.000000e+00, %tmp17
%tmp19 = load float, float addrspace(3)* %tmp9
%tmp20 = load float, float addrspace(3)* %tmp10
%tmp21 = fmul float %tmp19, %tmp20
%tmp22 = fsub float %tmp18, %tmp21
%tmp23 = load float, float addrspace(3)* %tmp11
%tmp24 = load float, float addrspace(3)* %tmp12
%tmp25 = fmul float %tmp23, %tmp24
%tmp26 = fsub float %tmp22, %tmp25
%tmp27 = load float, float addrspace(3)* %tmp13
%tmp28 = load float, float addrspace(3)* %tmp14
%tmp29 = fmul float %tmp27, %tmp28
%tmp30 = fsub float %tmp26, %tmp29
store float %tmp30, float addrspace(1)* %tmp
ret void
}
; Function Attrs: nounwind readnone
declare i32 @llvm.amdgcn.workgroup.id.x() #1