[llvm] [WIP][SPARC] Weaken emitted barriers for atomic ops (PR #154950)
via llvm-commits
llvm-commits at lists.llvm.org
Fri Aug 22 06:45:49 PDT 2025
https://github.com/koachan created https://github.com/llvm/llvm-project/pull/154950
Weaken barriers for atomic ops to the form that's just enough to enforce memory model constraints.
In particular, we try to avoid emitting expensive #StoreLoad barriers whenever possible.
The barriers emitted conform to V9's RMO and V8's PSO memory model, and is compatible with GCC's lowering.
A quick test with `pgbench` shows some small (up to about 4%), but consistent speedup.
>From 928bf41991324bcf225bb433afb1eff4e4dc173e Mon Sep 17 00:00:00 2001
From: Koakuma <koachan at protonmail.com>
Date: Sun, 17 Aug 2025 10:47:08 +0700
Subject: [PATCH 1/3] [WIP][SPARC] Weaken emitted barriers for atomic ops
Weaken barriers for atomic ops just to the form that's enough to enforce
the constraints, but no stronger. In particular, we try to avoid emitting
expensive #StoreLoad barriers whenever possible.
The barriers emitted still conform to V9's RMO and V8's PSO memory model,
and is compatible with GCC's lowering.
---
llvm/lib/Target/Sparc/SparcISelLowering.cpp | 25 ++
llvm/lib/Target/Sparc/SparcISelLowering.h | 5 +
llvm/lib/Target/Sparc/SparcInstrInfo.td | 26 +-
llvm/test/CodeGen/SPARC/atomics-ordering.ll | 289 ++++++++++++++++++++
4 files changed, 342 insertions(+), 3 deletions(-)
create mode 100644 llvm/test/CodeGen/SPARC/atomics-ordering.ll
diff --git a/llvm/lib/Target/Sparc/SparcISelLowering.cpp b/llvm/lib/Target/Sparc/SparcISelLowering.cpp
index dd221327dbdc6..e59b05817a3b0 100644
--- a/llvm/lib/Target/Sparc/SparcISelLowering.cpp
+++ b/llvm/lib/Target/Sparc/SparcISelLowering.cpp
@@ -33,7 +33,10 @@
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/Function.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
+#include "llvm/Support/AtomicOrdering.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/KnownBits.h"
using namespace llvm;
@@ -3562,3 +3565,25 @@ void SparcTargetLowering::AdjustInstrPostInstrSelection(MachineInstr &MI,
if (!Node->hasAnyUseOfValue(0))
MI.getOperand(0).setReg(SP::G0);
}
+
+Instruction *SparcTargetLowering::emitLeadingFence(IRBuilderBase &Builder,
+ Instruction *Inst,
+ AtomicOrdering Ord) const {
+ bool HasStoreSemantics = isa<AtomicRMWInst>(Inst) || isa<StoreInst>(Inst);
+ if (HasStoreSemantics && isReleaseOrStronger(Ord))
+ return Builder.CreateFence(AtomicOrdering::Release);
+ return nullptr;
+}
+
+Instruction *SparcTargetLowering::emitTrailingFence(IRBuilderBase &Builder,
+ Instruction *Inst,
+ AtomicOrdering Ord) const {
+ bool HasLoadSemantics = isa<AtomicRMWInst>(Inst) || isa<LoadInst>(Inst);
+ if (HasLoadSemantics && isAcquireOrStronger(Ord))
+ return Builder.CreateFence(AtomicOrdering::Acquire);
+
+ // SC plain stores would need a trailing full barrier.
+ if (isa<StoreInst>(Inst) && Ord == AtomicOrdering::SequentiallyConsistent)
+ return Builder.CreateFence(Ord);
+ return nullptr;
+}
diff --git a/llvm/lib/Target/Sparc/SparcISelLowering.h b/llvm/lib/Target/Sparc/SparcISelLowering.h
index 4017beb88ff31..73bd8ff6b24a4 100644
--- a/llvm/lib/Target/Sparc/SparcISelLowering.h
+++ b/llvm/lib/Target/Sparc/SparcISelLowering.h
@@ -182,6 +182,11 @@ namespace llvm {
bool isFMAFasterThanFMulAndFAdd(const MachineFunction &MF,
EVT VT) const override;
+ Instruction *emitLeadingFence(IRBuilderBase &Builder, Instruction *Inst,
+ AtomicOrdering Ord) const override;
+ Instruction *emitTrailingFence(IRBuilderBase &Builder, Instruction *Inst,
+ AtomicOrdering Ord) const override;
+
bool shouldInsertFencesForAtomic(const Instruction *I) const override {
// FIXME: We insert fences for each atomics and generate
// sub-optimal code for PSO/TSO. (Approximately nobody uses any
diff --git a/llvm/lib/Target/Sparc/SparcInstrInfo.td b/llvm/lib/Target/Sparc/SparcInstrInfo.td
index 1a32eafb0e83d..ff5af4bcd03cc 100644
--- a/llvm/lib/Target/Sparc/SparcInstrInfo.td
+++ b/llvm/lib/Target/Sparc/SparcInstrInfo.td
@@ -1957,12 +1957,32 @@ def : Pat<(i32 (zextloadi1 ADDRri:$src)), (LDUBri ADDRri:$src)>;
def : Pat<(store (i32 0), ADDRrr:$dst), (STrr ADDRrr:$dst, (i32 G0))>;
def : Pat<(store (i32 0), ADDRri:$dst), (STri ADDRri:$dst, (i32 G0))>;
-// store bar for all atomic_fence in V8.
-let Predicates = [HasNoV9] in
+// All load-type operations in V8 comes with implicit acquire semantics.
+let Predicates = [HasNoV9] in {
+ // Acquire -> nothing
+ // FIXME how to prevent this from actually emitting anything?
+ def : Pat<(atomic_fence (i32 4), timm), (NOP)>;
+ // Release / AcqRel -> stbar
+ def : Pat<(atomic_fence (i32 5), timm), (STBAR)>;
+ // AcqRel and stronger -> stbar; ldstub [%sp-1], %g0
+ // FIXME how to actually emit the ldstub?
def : Pat<(atomic_fence timm, timm), (STBAR)>;
+}
-let Predicates = [HasV9] in
+// We have to handle both 32 and 64-bit cases.
+let Predicates = [HasV9] in {
+ // Acquire -> membar #LoadLoad | #LoadStore
+ def : Pat<(atomic_fence (i32 4), timm), (MEMBARi 0x5)>;
+ def : Pat<(atomic_fence (i64 4), timm), (MEMBARi 0x5)>;
+ // Release -> membar #LoadStore | #StoreStore
+ def : Pat<(atomic_fence (i32 5), timm), (MEMBARi 0xc)>;
+ def : Pat<(atomic_fence (i64 5), timm), (MEMBARi 0xc)>;
+ // AcqRel -> membar #LoadLoad | #LoadStore | #StoreStore
+ def : Pat<(atomic_fence (i32 6), timm), (MEMBARi 0xd)>;
+ def : Pat<(atomic_fence (i64 6), timm), (MEMBARi 0xd)>;
+ // SeqCst -> membar #StoreLoad | #LoadLoad | #LoadStore | #StoreStore
def : Pat<(atomic_fence timm, timm), (MEMBARi 0xf)>;
+}
// atomic_load addr -> load addr
def : Pat<(i32 (atomic_load_azext_8 ADDRrr:$src)), (LDUBrr ADDRrr:$src)>;
diff --git a/llvm/test/CodeGen/SPARC/atomics-ordering.ll b/llvm/test/CodeGen/SPARC/atomics-ordering.ll
new file mode 100644
index 0000000000000..e3decd56ee613
--- /dev/null
+++ b/llvm/test/CodeGen/SPARC/atomics-ordering.ll
@@ -0,0 +1,289 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc < %s -mtriple=sparc -verify-machineinstrs | FileCheck %s --check-prefixes=SPARC32
+; RUN: llc < %s -mtriple=sparc -mcpu=leon4 -verify-machineinstrs | FileCheck %s --check-prefixes=SPARC32-LEON4
+; RUN: llc < %s -mtriple=sparc -mcpu=v9 -verify-machineinstrs | FileCheck %s --check-prefixes=SPARC32-V9
+; RUN: llc < %s -mtriple=sparcv9 -verify-machineinstrs | FileCheck %s --check-prefixes=SPARC64
+
+define i32 @load_acq(ptr %0) nounwind {
+; SPARC32-LABEL: load_acq:
+; SPARC32: ! %bb.0:
+; SPARC32-NEXT: save %sp, -96, %sp
+; SPARC32-NEXT: mov %i0, %o0
+; SPARC32-NEXT: call __atomic_load_4
+; SPARC32-NEXT: mov 2, %o1
+; SPARC32-NEXT: ret
+; SPARC32-NEXT: restore %g0, %o0, %o0
+;
+; SPARC32-LEON4-LABEL: load_acq:
+; SPARC32-LEON4: ! %bb.0:
+; SPARC32-LEON4-NEXT: ld [%o0], %o0
+; SPARC32-LEON4-NEXT: nop
+; SPARC32-LEON4-NEXT: retl
+; SPARC32-LEON4-NEXT: nop
+;
+; SPARC32-V9-LABEL: load_acq:
+; SPARC32-V9: ! %bb.0:
+; SPARC32-V9-NEXT: ld [%o0], %o0
+; SPARC32-V9-NEXT: membar #LoadLoad | #LoadStore
+; SPARC32-V9-NEXT: retl
+; SPARC32-V9-NEXT: nop
+;
+; SPARC64-LABEL: load_acq:
+; SPARC64: ! %bb.0:
+; SPARC64-NEXT: ld [%o0], %o0
+; SPARC64-NEXT: membar #LoadLoad | #LoadStore
+; SPARC64-NEXT: retl
+; SPARC64-NEXT: nop
+ %2 = load atomic i32, ptr %0 acquire, align 4
+ ret i32 %2
+}
+
+define i32 @load_sc(ptr %0) nounwind {
+; SPARC32-LABEL: load_sc:
+; SPARC32: ! %bb.0:
+; SPARC32-NEXT: save %sp, -96, %sp
+; SPARC32-NEXT: mov %i0, %o0
+; SPARC32-NEXT: call __atomic_load_4
+; SPARC32-NEXT: mov 5, %o1
+; SPARC32-NEXT: ret
+; SPARC32-NEXT: restore %g0, %o0, %o0
+;
+; SPARC32-LEON4-LABEL: load_sc:
+; SPARC32-LEON4: ! %bb.0:
+; SPARC32-LEON4-NEXT: ld [%o0], %o0
+; SPARC32-LEON4-NEXT: nop
+; SPARC32-LEON4-NEXT: retl
+; SPARC32-LEON4-NEXT: nop
+;
+; SPARC32-V9-LABEL: load_sc:
+; SPARC32-V9: ! %bb.0:
+; SPARC32-V9-NEXT: ld [%o0], %o0
+; SPARC32-V9-NEXT: membar #LoadLoad | #LoadStore
+; SPARC32-V9-NEXT: retl
+; SPARC32-V9-NEXT: nop
+;
+; SPARC64-LABEL: load_sc:
+; SPARC64: ! %bb.0:
+; SPARC64-NEXT: ld [%o0], %o0
+; SPARC64-NEXT: membar #LoadLoad | #LoadStore
+; SPARC64-NEXT: retl
+; SPARC64-NEXT: nop
+ %2 = load atomic i32, ptr %0 seq_cst, align 4
+ ret i32 %2
+}
+
+define void @store_rel(ptr %0, i32 %1) nounwind {
+; SPARC32-LABEL: store_rel:
+; SPARC32: ! %bb.0:
+; SPARC32-NEXT: save %sp, -96, %sp
+; SPARC32-NEXT: mov %i1, %o1
+; SPARC32-NEXT: mov %i0, %o0
+; SPARC32-NEXT: call __atomic_store_4
+; SPARC32-NEXT: mov 3, %o2
+; SPARC32-NEXT: ret
+; SPARC32-NEXT: restore
+;
+; SPARC32-LEON4-LABEL: store_rel:
+; SPARC32-LEON4: ! %bb.0:
+; SPARC32-LEON4-NEXT: stbar
+; SPARC32-LEON4-NEXT: retl
+; SPARC32-LEON4-NEXT: st %o1, [%o0]
+;
+; SPARC32-V9-LABEL: store_rel:
+; SPARC32-V9: ! %bb.0:
+; SPARC32-V9-NEXT: membar #LoadStore | #StoreStore
+; SPARC32-V9-NEXT: retl
+; SPARC32-V9-NEXT: st %o1, [%o0]
+;
+; SPARC64-LABEL: store_rel:
+; SPARC64: ! %bb.0:
+; SPARC64-NEXT: membar #LoadStore | #StoreStore
+; SPARC64-NEXT: retl
+; SPARC64-NEXT: st %o1, [%o0]
+ store atomic i32 %1, ptr %0 release, align 4
+ ret void
+}
+
+define void @store_sc(ptr %0, i32 %1) nounwind {
+; SPARC32-LABEL: store_sc:
+; SPARC32: ! %bb.0:
+; SPARC32-NEXT: save %sp, -96, %sp
+; SPARC32-NEXT: mov %i1, %o1
+; SPARC32-NEXT: mov %i0, %o0
+; SPARC32-NEXT: call __atomic_store_4
+; SPARC32-NEXT: mov 5, %o2
+; SPARC32-NEXT: ret
+; SPARC32-NEXT: restore
+;
+; SPARC32-LEON4-LABEL: store_sc:
+; SPARC32-LEON4: ! %bb.0:
+; SPARC32-LEON4-NEXT: stbar
+; SPARC32-LEON4-NEXT: st %o1, [%o0]
+; SPARC32-LEON4-NEXT: stbar
+; SPARC32-LEON4-NEXT: retl
+; SPARC32-LEON4-NEXT: nop
+;
+; SPARC32-V9-LABEL: store_sc:
+; SPARC32-V9: ! %bb.0:
+; SPARC32-V9-NEXT: membar #LoadStore | #StoreStore
+; SPARC32-V9-NEXT: st %o1, [%o0]
+; SPARC32-V9-NEXT: membar #LoadLoad | #StoreLoad | #LoadStore | #StoreStore
+; SPARC32-V9-NEXT: retl
+; SPARC32-V9-NEXT: nop
+;
+; SPARC64-LABEL: store_sc:
+; SPARC64: ! %bb.0:
+; SPARC64-NEXT: membar #LoadStore | #StoreStore
+; SPARC64-NEXT: st %o1, [%o0]
+; SPARC64-NEXT: membar #LoadLoad | #StoreLoad | #LoadStore | #StoreStore
+; SPARC64-NEXT: retl
+; SPARC64-NEXT: nop
+ store atomic i32 %1, ptr %0 seq_cst, align 4
+ ret void
+}
+
+define i32 @rmw_acq(ptr %0, i32 %1) nounwind {
+; SPARC32-LABEL: rmw_acq:
+; SPARC32: ! %bb.0:
+; SPARC32-NEXT: save %sp, -96, %sp
+; SPARC32-NEXT: mov %i1, %o1
+; SPARC32-NEXT: mov %i0, %o0
+; SPARC32-NEXT: call __atomic_exchange_4
+; SPARC32-NEXT: mov 2, %o2
+; SPARC32-NEXT: ret
+; SPARC32-NEXT: restore %g0, %o0, %o0
+;
+; SPARC32-LEON4-LABEL: rmw_acq:
+; SPARC32-LEON4: ! %bb.0:
+; SPARC32-LEON4-NEXT: swap [%o0], %o1
+; SPARC32-LEON4-NEXT: nop
+; SPARC32-LEON4-NEXT: retl
+; SPARC32-LEON4-NEXT: mov %o1, %o0
+;
+; SPARC32-V9-LABEL: rmw_acq:
+; SPARC32-V9: ! %bb.0:
+; SPARC32-V9-NEXT: swap [%o0], %o1
+; SPARC32-V9-NEXT: membar #LoadLoad | #LoadStore
+; SPARC32-V9-NEXT: retl
+; SPARC32-V9-NEXT: mov %o1, %o0
+;
+; SPARC64-LABEL: rmw_acq:
+; SPARC64: ! %bb.0:
+; SPARC64-NEXT: swap [%o0], %o1
+; SPARC64-NEXT: membar #LoadLoad | #LoadStore
+; SPARC64-NEXT: retl
+; SPARC64-NEXT: mov %o1, %o0
+ %3 = atomicrmw xchg ptr %0, i32 %1 acquire, align 4
+ ret i32 %3
+}
+
+define i32 @rmw_rel(ptr %0, i32 %1) nounwind {
+; SPARC32-LABEL: rmw_rel:
+; SPARC32: ! %bb.0:
+; SPARC32-NEXT: save %sp, -96, %sp
+; SPARC32-NEXT: mov %i1, %o1
+; SPARC32-NEXT: mov %i0, %o0
+; SPARC32-NEXT: call __atomic_exchange_4
+; SPARC32-NEXT: mov 3, %o2
+; SPARC32-NEXT: ret
+; SPARC32-NEXT: restore %g0, %o0, %o0
+;
+; SPARC32-LEON4-LABEL: rmw_rel:
+; SPARC32-LEON4: ! %bb.0:
+; SPARC32-LEON4-NEXT: stbar
+; SPARC32-LEON4-NEXT: swap [%o0], %o1
+; SPARC32-LEON4-NEXT: retl
+; SPARC32-LEON4-NEXT: mov %o1, %o0
+;
+; SPARC32-V9-LABEL: rmw_rel:
+; SPARC32-V9: ! %bb.0:
+; SPARC32-V9-NEXT: membar #LoadStore | #StoreStore
+; SPARC32-V9-NEXT: swap [%o0], %o1
+; SPARC32-V9-NEXT: retl
+; SPARC32-V9-NEXT: mov %o1, %o0
+;
+; SPARC64-LABEL: rmw_rel:
+; SPARC64: ! %bb.0:
+; SPARC64-NEXT: membar #LoadStore | #StoreStore
+; SPARC64-NEXT: swap [%o0], %o1
+; SPARC64-NEXT: retl
+; SPARC64-NEXT: mov %o1, %o0
+ %3 = atomicrmw xchg ptr %0, i32 %1 release, align 4
+ ret i32 %3
+}
+
+define i32 @rmw_acq_rel(ptr %0, i32 %1) nounwind {
+; SPARC32-LABEL: rmw_acq_rel:
+; SPARC32: ! %bb.0:
+; SPARC32-NEXT: save %sp, -96, %sp
+; SPARC32-NEXT: mov %i1, %o1
+; SPARC32-NEXT: mov %i0, %o0
+; SPARC32-NEXT: call __atomic_exchange_4
+; SPARC32-NEXT: mov 4, %o2
+; SPARC32-NEXT: ret
+; SPARC32-NEXT: restore %g0, %o0, %o0
+;
+; SPARC32-LEON4-LABEL: rmw_acq_rel:
+; SPARC32-LEON4: ! %bb.0:
+; SPARC32-LEON4-NEXT: stbar
+; SPARC32-LEON4-NEXT: swap [%o0], %o1
+; SPARC32-LEON4-NEXT: nop
+; SPARC32-LEON4-NEXT: retl
+; SPARC32-LEON4-NEXT: mov %o1, %o0
+;
+; SPARC32-V9-LABEL: rmw_acq_rel:
+; SPARC32-V9: ! %bb.0:
+; SPARC32-V9-NEXT: membar #LoadStore | #StoreStore
+; SPARC32-V9-NEXT: swap [%o0], %o1
+; SPARC32-V9-NEXT: membar #LoadLoad | #LoadStore
+; SPARC32-V9-NEXT: retl
+; SPARC32-V9-NEXT: mov %o1, %o0
+;
+; SPARC64-LABEL: rmw_acq_rel:
+; SPARC64: ! %bb.0:
+; SPARC64-NEXT: membar #LoadStore | #StoreStore
+; SPARC64-NEXT: swap [%o0], %o1
+; SPARC64-NEXT: membar #LoadLoad | #LoadStore
+; SPARC64-NEXT: retl
+; SPARC64-NEXT: mov %o1, %o0
+ %3 = atomicrmw xchg ptr %0, i32 %1 acq_rel, align 4
+ ret i32 %3
+}
+
+define i32 @rmw_sc(ptr %0, i32 %1) nounwind {
+; SPARC32-LABEL: rmw_sc:
+; SPARC32: ! %bb.0:
+; SPARC32-NEXT: save %sp, -96, %sp
+; SPARC32-NEXT: mov %i1, %o1
+; SPARC32-NEXT: mov %i0, %o0
+; SPARC32-NEXT: call __atomic_exchange_4
+; SPARC32-NEXT: mov 5, %o2
+; SPARC32-NEXT: ret
+; SPARC32-NEXT: restore %g0, %o0, %o0
+;
+; SPARC32-LEON4-LABEL: rmw_sc:
+; SPARC32-LEON4: ! %bb.0:
+; SPARC32-LEON4-NEXT: stbar
+; SPARC32-LEON4-NEXT: swap [%o0], %o1
+; SPARC32-LEON4-NEXT: nop
+; SPARC32-LEON4-NEXT: retl
+; SPARC32-LEON4-NEXT: mov %o1, %o0
+;
+; SPARC32-V9-LABEL: rmw_sc:
+; SPARC32-V9: ! %bb.0:
+; SPARC32-V9-NEXT: membar #LoadStore | #StoreStore
+; SPARC32-V9-NEXT: swap [%o0], %o1
+; SPARC32-V9-NEXT: membar #LoadLoad | #LoadStore
+; SPARC32-V9-NEXT: retl
+; SPARC32-V9-NEXT: mov %o1, %o0
+;
+; SPARC64-LABEL: rmw_sc:
+; SPARC64: ! %bb.0:
+; SPARC64-NEXT: membar #LoadStore | #StoreStore
+; SPARC64-NEXT: swap [%o0], %o1
+; SPARC64-NEXT: membar #LoadLoad | #LoadStore
+; SPARC64-NEXT: retl
+; SPARC64-NEXT: mov %o1, %o0
+ %3 = atomicrmw xchg ptr %0, i32 %1 seq_cst, align 4
+ ret i32 %3
+}
>From b21acd74c4883ce6f350ae37c6ab561dae197dc3 Mon Sep 17 00:00:00 2001
From: Koakuma <koachan at protonmail.com>
Date: Thu, 21 Aug 2025 23:43:58 +0700
Subject: [PATCH 2/3] Update tests
---
.../CodeGen/SPARC/atomicrmw-uinc-udec-wrap.ll | 24 +++++++++----------
1 file changed, 12 insertions(+), 12 deletions(-)
diff --git a/llvm/test/CodeGen/SPARC/atomicrmw-uinc-udec-wrap.ll b/llvm/test/CodeGen/SPARC/atomicrmw-uinc-udec-wrap.ll
index 380a4a0a6b870..d1f1c46d9b8b1 100644
--- a/llvm/test/CodeGen/SPARC/atomicrmw-uinc-udec-wrap.ll
+++ b/llvm/test/CodeGen/SPARC/atomicrmw-uinc-udec-wrap.ll
@@ -5,7 +5,7 @@ define i8 @atomicrmw_uinc_wrap_i8(ptr %ptr, i8 %val) {
; CHECK-LABEL: atomicrmw_uinc_wrap_i8:
; CHECK: .cfi_startproc
; CHECK-NEXT: ! %bb.0:
-; CHECK-NEXT: membar #LoadLoad | #StoreLoad | #LoadStore | #StoreStore
+; CHECK-NEXT: membar #LoadStore | #StoreStore
; CHECK-NEXT: and %o0, -4, %o2
; CHECK-NEXT: mov 3, %o3
; CHECK-NEXT: andn %o3, %o0, %o0
@@ -36,7 +36,7 @@ define i8 @atomicrmw_uinc_wrap_i8(ptr %ptr, i8 %val) {
; CHECK-NEXT: nop
; CHECK-NEXT: ! %bb.2: ! %atomicrmw.end
; CHECK-NEXT: srl %o4, %o0, %o0
-; CHECK-NEXT: membar #LoadLoad | #StoreLoad | #LoadStore | #StoreStore
+; CHECK-NEXT: membar #LoadLoad | #LoadStore
; CHECK-NEXT: retl
; CHECK-NEXT: nop
%result = atomicrmw uinc_wrap ptr %ptr, i8 %val seq_cst
@@ -47,7 +47,7 @@ define i16 @atomicrmw_uinc_wrap_i16(ptr %ptr, i16 %val) {
; CHECK-LABEL: atomicrmw_uinc_wrap_i16:
; CHECK: .cfi_startproc
; CHECK-NEXT: ! %bb.0:
-; CHECK-NEXT: membar #LoadLoad | #StoreLoad | #LoadStore | #StoreStore
+; CHECK-NEXT: membar #LoadStore | #StoreStore
; CHECK-NEXT: and %o0, -4, %o2
; CHECK-NEXT: and %o0, 3, %o0
; CHECK-NEXT: xor %o0, 2, %o0
@@ -79,7 +79,7 @@ define i16 @atomicrmw_uinc_wrap_i16(ptr %ptr, i16 %val) {
; CHECK-NEXT: nop
; CHECK-NEXT: ! %bb.2: ! %atomicrmw.end
; CHECK-NEXT: srl %o5, %o0, %o0
-; CHECK-NEXT: membar #LoadLoad | #StoreLoad | #LoadStore | #StoreStore
+; CHECK-NEXT: membar #LoadLoad | #LoadStore
; CHECK-NEXT: retl
; CHECK-NEXT: nop
%result = atomicrmw uinc_wrap ptr %ptr, i16 %val seq_cst
@@ -90,7 +90,7 @@ define i32 @atomicrmw_uinc_wrap_i32(ptr %ptr, i32 %val) {
; CHECK-LABEL: atomicrmw_uinc_wrap_i32:
; CHECK: .cfi_startproc
; CHECK-NEXT: ! %bb.0:
-; CHECK-NEXT: membar #LoadLoad | #StoreLoad | #LoadStore | #StoreStore
+; CHECK-NEXT: membar #LoadStore | #StoreStore
; CHECK-NEXT: ld [%o0], %o2
; CHECK-NEXT: .LBB2_1: ! %atomicrmw.start
; CHECK-NEXT: ! =>This Inner Loop Header: Depth=1
@@ -106,7 +106,7 @@ define i32 @atomicrmw_uinc_wrap_i32(ptr %ptr, i32 %val) {
; CHECK-NEXT: bne %icc, .LBB2_1
; CHECK-NEXT: nop
; CHECK-NEXT: ! %bb.2: ! %atomicrmw.end
-; CHECK-NEXT: membar #LoadLoad | #StoreLoad | #LoadStore | #StoreStore
+; CHECK-NEXT: membar #LoadLoad | #LoadStore
; CHECK-NEXT: retl
; CHECK-NEXT: mov %o2, %o0
%result = atomicrmw uinc_wrap ptr %ptr, i32 %val seq_cst
@@ -160,7 +160,7 @@ define i8 @atomicrmw_udec_wrap_i8(ptr %ptr, i8 %val) {
; CHECK-LABEL: atomicrmw_udec_wrap_i8:
; CHECK: .cfi_startproc
; CHECK-NEXT: ! %bb.0:
-; CHECK-NEXT: membar #LoadLoad | #StoreLoad | #LoadStore | #StoreStore
+; CHECK-NEXT: membar #LoadStore | #StoreStore
; CHECK-NEXT: and %o0, -4, %o2
; CHECK-NEXT: mov 3, %o3
; CHECK-NEXT: andn %o3, %o0, %o0
@@ -193,7 +193,7 @@ define i8 @atomicrmw_udec_wrap_i8(ptr %ptr, i8 %val) {
; CHECK-NEXT: nop
; CHECK-NEXT: ! %bb.2: ! %atomicrmw.end
; CHECK-NEXT: srl %o5, %o0, %o0
-; CHECK-NEXT: membar #LoadLoad | #StoreLoad | #LoadStore | #StoreStore
+; CHECK-NEXT: membar #LoadLoad | #LoadStore
; CHECK-NEXT: retl
; CHECK-NEXT: nop
%result = atomicrmw udec_wrap ptr %ptr, i8 %val seq_cst
@@ -204,7 +204,7 @@ define i16 @atomicrmw_udec_wrap_i16(ptr %ptr, i16 %val) {
; CHECK-LABEL: atomicrmw_udec_wrap_i16:
; CHECK: .cfi_startproc
; CHECK-NEXT: ! %bb.0:
-; CHECK-NEXT: membar #LoadLoad | #StoreLoad | #LoadStore | #StoreStore
+; CHECK-NEXT: membar #LoadStore | #StoreStore
; CHECK-NEXT: and %o0, -4, %o2
; CHECK-NEXT: and %o0, 3, %o0
; CHECK-NEXT: xor %o0, 2, %o0
@@ -238,7 +238,7 @@ define i16 @atomicrmw_udec_wrap_i16(ptr %ptr, i16 %val) {
; CHECK-NEXT: nop
; CHECK-NEXT: ! %bb.2: ! %atomicrmw.end
; CHECK-NEXT: srl %g2, %o0, %o0
-; CHECK-NEXT: membar #LoadLoad | #StoreLoad | #LoadStore | #StoreStore
+; CHECK-NEXT: membar #LoadLoad | #LoadStore
; CHECK-NEXT: retl
; CHECK-NEXT: nop
%result = atomicrmw udec_wrap ptr %ptr, i16 %val seq_cst
@@ -249,7 +249,7 @@ define i32 @atomicrmw_udec_wrap_i32(ptr %ptr, i32 %val) {
; CHECK-LABEL: atomicrmw_udec_wrap_i32:
; CHECK: .cfi_startproc
; CHECK-NEXT: ! %bb.0:
-; CHECK-NEXT: membar #LoadLoad | #StoreLoad | #LoadStore | #StoreStore
+; CHECK-NEXT: membar #LoadStore | #StoreStore
; CHECK-NEXT: ld [%o0], %o2
; CHECK-NEXT: .LBB6_1: ! %atomicrmw.start
; CHECK-NEXT: ! =>This Inner Loop Header: Depth=1
@@ -267,7 +267,7 @@ define i32 @atomicrmw_udec_wrap_i32(ptr %ptr, i32 %val) {
; CHECK-NEXT: bne %icc, .LBB6_1
; CHECK-NEXT: nop
; CHECK-NEXT: ! %bb.2: ! %atomicrmw.end
-; CHECK-NEXT: membar #LoadLoad | #StoreLoad | #LoadStore | #StoreStore
+; CHECK-NEXT: membar #LoadLoad | #LoadStore
; CHECK-NEXT: retl
; CHECK-NEXT: mov %o2, %o0
%result = atomicrmw udec_wrap ptr %ptr, i32 %val seq_cst
>From d78147f08bb047ee6cae49a360bbf5e4de644d09 Mon Sep 17 00:00:00 2001
From: Koakuma <koachan at protonmail.com>
Date: Fri, 22 Aug 2025 20:34:58 +0700
Subject: [PATCH 3/3] Don't emit acq barriers on V8
---
llvm/lib/Target/Sparc/SparcISelLowering.cpp | 4 +++-
llvm/lib/Target/Sparc/SparcInstrInfo.td | 3 +--
llvm/test/CodeGen/SPARC/atomics-ordering.ll | 11 ++---------
3 files changed, 6 insertions(+), 12 deletions(-)
diff --git a/llvm/lib/Target/Sparc/SparcISelLowering.cpp b/llvm/lib/Target/Sparc/SparcISelLowering.cpp
index e59b05817a3b0..a926fe56a61ef 100644
--- a/llvm/lib/Target/Sparc/SparcISelLowering.cpp
+++ b/llvm/lib/Target/Sparc/SparcISelLowering.cpp
@@ -3578,8 +3578,10 @@ Instruction *SparcTargetLowering::emitLeadingFence(IRBuilderBase &Builder,
Instruction *SparcTargetLowering::emitTrailingFence(IRBuilderBase &Builder,
Instruction *Inst,
AtomicOrdering Ord) const {
+ // V8 loads already come with implicit acquire barrier so there's no need to
+ // emit it again.
bool HasLoadSemantics = isa<AtomicRMWInst>(Inst) || isa<LoadInst>(Inst);
- if (HasLoadSemantics && isAcquireOrStronger(Ord))
+ if (Subtarget->isV9() && HasLoadSemantics && isAcquireOrStronger(Ord))
return Builder.CreateFence(AtomicOrdering::Acquire);
// SC plain stores would need a trailing full barrier.
diff --git a/llvm/lib/Target/Sparc/SparcInstrInfo.td b/llvm/lib/Target/Sparc/SparcInstrInfo.td
index ff5af4bcd03cc..f427f6bfba63b 100644
--- a/llvm/lib/Target/Sparc/SparcInstrInfo.td
+++ b/llvm/lib/Target/Sparc/SparcInstrInfo.td
@@ -1959,8 +1959,7 @@ def : Pat<(store (i32 0), ADDRri:$dst), (STri ADDRri:$dst, (i32 G0))>;
// All load-type operations in V8 comes with implicit acquire semantics.
let Predicates = [HasNoV9] in {
- // Acquire -> nothing
- // FIXME how to prevent this from actually emitting anything?
+ // Acquire -> nop
def : Pat<(atomic_fence (i32 4), timm), (NOP)>;
// Release / AcqRel -> stbar
def : Pat<(atomic_fence (i32 5), timm), (STBAR)>;
diff --git a/llvm/test/CodeGen/SPARC/atomics-ordering.ll b/llvm/test/CodeGen/SPARC/atomics-ordering.ll
index e3decd56ee613..25a370b325302 100644
--- a/llvm/test/CodeGen/SPARC/atomics-ordering.ll
+++ b/llvm/test/CodeGen/SPARC/atomics-ordering.ll
@@ -16,10 +16,8 @@ define i32 @load_acq(ptr %0) nounwind {
;
; SPARC32-LEON4-LABEL: load_acq:
; SPARC32-LEON4: ! %bb.0:
-; SPARC32-LEON4-NEXT: ld [%o0], %o0
-; SPARC32-LEON4-NEXT: nop
; SPARC32-LEON4-NEXT: retl
-; SPARC32-LEON4-NEXT: nop
+; SPARC32-LEON4-NEXT: ld [%o0], %o0
;
; SPARC32-V9-LABEL: load_acq:
; SPARC32-V9: ! %bb.0:
@@ -50,10 +48,8 @@ define i32 @load_sc(ptr %0) nounwind {
;
; SPARC32-LEON4-LABEL: load_sc:
; SPARC32-LEON4: ! %bb.0:
-; SPARC32-LEON4-NEXT: ld [%o0], %o0
-; SPARC32-LEON4-NEXT: nop
; SPARC32-LEON4-NEXT: retl
-; SPARC32-LEON4-NEXT: nop
+; SPARC32-LEON4-NEXT: ld [%o0], %o0
;
; SPARC32-V9-LABEL: load_sc:
; SPARC32-V9: ! %bb.0:
@@ -156,7 +152,6 @@ define i32 @rmw_acq(ptr %0, i32 %1) nounwind {
; SPARC32-LEON4-LABEL: rmw_acq:
; SPARC32-LEON4: ! %bb.0:
; SPARC32-LEON4-NEXT: swap [%o0], %o1
-; SPARC32-LEON4-NEXT: nop
; SPARC32-LEON4-NEXT: retl
; SPARC32-LEON4-NEXT: mov %o1, %o0
;
@@ -227,7 +222,6 @@ define i32 @rmw_acq_rel(ptr %0, i32 %1) nounwind {
; SPARC32-LEON4: ! %bb.0:
; SPARC32-LEON4-NEXT: stbar
; SPARC32-LEON4-NEXT: swap [%o0], %o1
-; SPARC32-LEON4-NEXT: nop
; SPARC32-LEON4-NEXT: retl
; SPARC32-LEON4-NEXT: mov %o1, %o0
;
@@ -265,7 +259,6 @@ define i32 @rmw_sc(ptr %0, i32 %1) nounwind {
; SPARC32-LEON4: ! %bb.0:
; SPARC32-LEON4-NEXT: stbar
; SPARC32-LEON4-NEXT: swap [%o0], %o1
-; SPARC32-LEON4-NEXT: nop
; SPARC32-LEON4-NEXT: retl
; SPARC32-LEON4-NEXT: mov %o1, %o0
;
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