[llvm-branch-commits] [llvm] AMDGPU: Add a subtarget feature for fine-grained remote memory support (PR #96442)

[Matt Arsenault via llvm-branch-commits]

https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/96442

Atomic access to fine-grained remote memory does not work on all
subtargets. Add a feature for targets where this is expected to work.

>From 2da0565165d97cded02896b18a9d7f8083474da9 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Sun, 23 Jun 2024 22:02:36 +0200
Subject: [PATCH] AMDGPU: Add a subtarget feature for fine-grained remote
 memory support

Atomic access to fine-grained remote memory does not work on all
subtargets. Add a feature for targets where this is expected to work.
---
 llvm/lib/Target/AMDGPU/AMDGPU.td      | 14 ++++++++++++--
 llvm/lib/Target/AMDGPU/GCNSubtarget.h |  8 ++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Target/AMDGPU/AMDGPU.td b/llvm/lib/Target/AMDGPU/AMDGPU.td
index 5bc0fe8bba608..7ff861f5b144d 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPU.td
+++ b/llvm/lib/Target/AMDGPU/AMDGPU.td
@@ -788,6 +788,14 @@ def FeatureFlatAtomicFaddF32Inst
   "Has flat_atomic_add_f32 instruction"
 >;
 
+def FeatureAgentScopeFineGrainedRemoteMemoryAtomics
+  : SubtargetFeature<"agent-scope-fine-grained-remote-memory-atomics",
+  "HasAgentScopeFineGrainedRemoteMemoryAtomics",
+  "true",
+  "Agent (device) scoped atomic operations not directly supported by "
+  "PCIe work for allocations in host or peer PCIe device memory"
+>;
+
 def FeatureDefaultComponentZero : SubtargetFeature<"default-component-zero",
   "HasDefaultComponentZero",
   "true",
@@ -1207,7 +1215,8 @@ def FeatureGFX12 : GCNSubtargetFeatureGeneration<"GFX12",
    FeatureUnalignedBufferAccess, FeatureUnalignedDSAccess,
    FeatureTrue16BitInsts, FeatureDefaultComponentBroadcast,
    FeatureMaxHardClauseLength32,
-   FeatureAtomicFMinFMaxF32GlobalInsts, FeatureAtomicFMinFMaxF32FlatInsts
+   FeatureAtomicFMinFMaxF32GlobalInsts, FeatureAtomicFMinFMaxF32FlatInsts,
+   FeatureAgentScopeFineGrainedRemoteMemoryAtomics
   ]
 >;
 
@@ -1415,7 +1424,8 @@ def FeatureISAVersion9_4_Common : FeatureSet<
    FeatureBackOffBarrier,
    FeatureKernargPreload,
    FeatureAtomicFMinFMaxF64GlobalInsts,
-   FeatureAtomicFMinFMaxF64FlatInsts
+   FeatureAtomicFMinFMaxF64FlatInsts,
+   FeatureAgentScopeFineGrainedRemoteMemoryAtomics
    ]>;
 
 def FeatureISAVersion9_4_0 : FeatureSet<
diff --git a/llvm/lib/Target/AMDGPU/GCNSubtarget.h b/llvm/lib/Target/AMDGPU/GCNSubtarget.h
index 966708db4f37c..c40efbdcf7f0b 100644
--- a/llvm/lib/Target/AMDGPU/GCNSubtarget.h
+++ b/llvm/lib/Target/AMDGPU/GCNSubtarget.h
@@ -174,6 +174,7 @@ class GCNSubtarget final : public AMDGPUGenSubtargetInfo,
   bool HasAtomicBufferPkAddBF16Inst = false;
   bool HasFlatAtomicFaddF32Inst = false;
   bool HasDefaultComponentZero = false;
+  bool HasAgentScopeFineGrainedRemoteMemoryAtomics = false;
   bool HasDefaultComponentBroadcast = false;
   /// The maximum number of instructions that may be placed within an S_CLAUSE,
   /// which is one greater than the maximum argument to S_CLAUSE. A value of 0
@@ -871,6 +872,13 @@ class GCNSubtarget final : public AMDGPUGenSubtargetInfo,
 
   bool hasFlatAtomicFaddF32Inst() const { return HasFlatAtomicFaddF32Inst; }
 
+  /// \return true if atomic operations targeting fine-grained memory work
+  /// correctly at device scope, in allocations in host or peer PCIe device
+  /// memory.
+  bool supportsAgentScopeFineGrainedRemoteMemoryAtomics() const {
+    return HasAgentScopeFineGrainedRemoteMemoryAtomics;
+  }
+
   bool hasDefaultComponentZero() const { return HasDefaultComponentZero; }
 
   bool hasDefaultComponentBroadcast() const {