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[AMDGPU] Fix no waitcnt produced between LDS DMA and ds_read on gfx10 #75245
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BUFFER_LOAD_DWORD_LDS was incorrectly touching vscnt instead of the vmcnt. This is VMEM load and DS store, so it shall use vmcnt.
@llvm/pr-subscribers-backend-amdgpu Author: Stanislav Mekhanoshin (rampitec) ChangesBUFFER_LOAD_DWORD_LDS was incorrectly touching vscnt instead of the vmcnt. This is VMEM load and DS store, so it shall use vmcnt. Full diff: https://github.com/llvm/llvm-project/pull/75245.diff 3 Files Affected:
diff --git a/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp b/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp
index ede4841b8a5fd..8967369cf21b6 100644
--- a/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp
+++ b/llvm/lib/Target/AMDGPU/SIInsertWaitcnts.cpp
@@ -452,7 +452,9 @@ class SIInsertWaitcnts : public MachineFunctionPass {
// FLAT instruction.
WaitEventType getVmemWaitEventType(const MachineInstr &Inst) const {
assert(SIInstrInfo::isVMEM(Inst) || SIInstrInfo::isFLAT(Inst));
- if (!ST->hasVscnt())
+ // LDS DMA loads are also stores, but on the LDS side. On the VMEM side
+ // these should use VM_CNT.
+ if (!ST->hasVscnt() || SIInstrInfo::mayWriteLDSThroughDMA(Inst))
return VMEM_ACCESS;
if (Inst.mayStore() && !SIInstrInfo::isAtomicRet(Inst)) {
// FLAT and SCRATCH instructions may access scratch. Other VMEM
@@ -544,14 +546,6 @@ void WaitcntBrackets::setExpScore(const MachineInstr *MI,
}
}
-// MUBUF and FLAT LDS DMA operations need a wait on vmcnt before LDS written
-// can be accessed. A load from LDS to VMEM does not need a wait.
-static bool mayWriteLDSThroughDMA(const MachineInstr &MI) {
- return SIInstrInfo::isVALU(MI) &&
- (SIInstrInfo::isMUBUF(MI) || SIInstrInfo::isFLAT(MI)) &&
- MI.getOpcode() != AMDGPU::BUFFER_STORE_LDS_DWORD;
-}
-
void WaitcntBrackets::updateByEvent(const SIInstrInfo *TII,
const SIRegisterInfo *TRI,
const MachineRegisterInfo *MRI,
@@ -703,7 +697,10 @@ void WaitcntBrackets::updateByEvent(const SIInstrInfo *TII,
setRegScore(RegNo, T, CurrScore);
}
}
- if (Inst.mayStore() && (TII->isDS(Inst) || mayWriteLDSThroughDMA(Inst))) {
+ if (Inst.mayStore() &&
+ (TII->isDS(Inst) || TII->mayWriteLDSThroughDMA(Inst))) {
+ // MUBUF and FLAT LDS DMA operations need a wait on vmcnt before LDS
+ // written can be accessed. A load from LDS to VMEM does not need a wait.
setRegScore(SQ_MAX_PGM_VGPRS + EXTRA_VGPR_LDS, T, CurrScore);
}
}
@@ -1178,7 +1175,7 @@ bool SIInsertWaitcnts::generateWaitcntInstBefore(MachineInstr &MI,
if (AS != AMDGPUAS::LOCAL_ADDRESS && AS != AMDGPUAS::FLAT_ADDRESS)
continue;
// No need to wait before load from VMEM to LDS.
- if (mayWriteLDSThroughDMA(MI))
+ if (TII->mayWriteLDSThroughDMA(MI))
continue;
unsigned RegNo = SQ_MAX_PGM_VGPRS + EXTRA_VGPR_LDS;
// VM_CNT is only relevant to vgpr or LDS.
diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.h b/llvm/lib/Target/AMDGPU/SIInstrInfo.h
index e794d8cf7cc22..32a81d67cc246 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrInfo.h
+++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.h
@@ -546,6 +546,14 @@ class SIInstrInfo final : public AMDGPUGenInstrInfo {
return get(Opcode).TSFlags & SIInstrFlags::DS;
}
+ static bool isLDSDMA(const MachineInstr &MI) {
+ return isVALU(MI) && (isMUBUF(MI) || isFLAT(MI));
+ }
+
+ bool isLDSDMA(uint16_t Opcode) {
+ return isVALU(Opcode) && (isMUBUF(Opcode) || isFLAT(Opcode));
+ }
+
static bool isGWS(const MachineInstr &MI) {
return MI.getDesc().TSFlags & SIInstrFlags::GWS;
}
@@ -667,6 +675,10 @@ class SIInstrInfo final : public AMDGPUGenInstrInfo {
SIInstrFlags::IsAtomicNoRet);
}
+ static bool mayWriteLDSThroughDMA(const MachineInstr &MI) {
+ return isLDSDMA(MI) && MI.getOpcode() != AMDGPU::BUFFER_STORE_LDS_DWORD;
+ }
+
static bool isWQM(const MachineInstr &MI) {
return MI.getDesc().TSFlags & SIInstrFlags::WQM;
}
diff --git a/llvm/test/CodeGen/AMDGPU/lds-dma-waits.ll b/llvm/test/CodeGen/AMDGPU/lds-dma-waits.ll
index 688f0314f7d8f..58c6406fac7aa 100644
--- a/llvm/test/CodeGen/AMDGPU/lds-dma-waits.ll
+++ b/llvm/test/CodeGen/AMDGPU/lds-dma-waits.ll
@@ -9,15 +9,10 @@ declare void @llvm.amdgcn.global.load.lds(ptr addrspace(1) nocapture %gptr, ptr
; FIXME: vmcnt(0) is too strong, it shall use vmcnt(2) before the first
; ds_read_b32 and vmcnt(0) before the second.
-; FIXME: GFX10 does not get a waitcount at all.
; GCN-LABEL: {{^}}buffer_load_lds_dword_2_arrays:
; GCN-COUNT-4: buffer_load_dword
-; GFX9: s_waitcnt vmcnt(0)
-
-; FIXME:
-; GFX10-NOT: s_waitcnt
-
+; GCN: s_waitcnt vmcnt(0)
; GCN: ds_read_b32
; FIXME:
@@ -49,9 +44,9 @@ main_body:
; GFX9: s_waitcnt vmcnt(0)
; GFX9-COUNT-2: ds_read_b32
-; FIXME:
-; GFX10-NOT: s_waitcnt
+; FIXME: can be vmcnt(2)
+; GFX10: s_waitcnt vmcnt(0)
; GFX10: ds_read_b32
; FIXME:
|
jayfoad
approved these changes
Dec 13, 2023
searlmc1
pushed a commit
to ROCm/llvm-project
that referenced
this pull request
Feb 6, 2024
…llvm#75245) BUFFER_LOAD_DWORD_LDS was incorrectly touching vscnt instead of the vmcnt. This is VMEM load and DS store, so it shall use vmcnt. Change-Id: I9956cd3478b8edc79ffafb3c8ef6e7319ed66219
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BUFFER_LOAD_DWORD_LDS was incorrectly touching vscnt instead of the vmcnt. This is VMEM load and DS store, so it shall use vmcnt.