[llvm] r370272 - [WebAssembly] Add atomic.fence instruction
Heejin Ahn via llvm-commits
llvm-commits at lists.llvm.org
Wed Aug 28 16:13:43 PDT 2019
Author: aheejin
Date: Wed Aug 28 16:13:43 2019
New Revision: 370272
URL: http://llvm.org/viewvc/llvm-project?rev=370272&view=rev
Log:
[WebAssembly] Add atomic.fence instruction
Summary:
This adds `atomic.fence` instruction:
https://github.com/WebAssembly/threads/blob/master/proposals/threads/Overview.md#fence-operator
And we now emit the new `atomic.fence` instruction for multithread
fences, rather than the prevous `atomic.rmw` hack.
Reviewers: dschuff
Subscribers: sbc100, jgravelle-google, hiraditya, sunfish, jfb, tlively, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D66794
Added:
llvm/trunk/test/CodeGen/WebAssembly/atomic-fence.mir
Modified:
llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp
llvm/trunk/lib/Target/WebAssembly/WebAssemblyInstrAtomics.td
llvm/trunk/test/CodeGen/WebAssembly/atomic-fence.ll
llvm/trunk/test/MC/WebAssembly/atomics-encodings.s
Modified: llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp?rev=370272&r1=370271&r2=370272&view=diff
==============================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp (original)
+++ llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp Wed Aug 28 16:13:43 2019
@@ -88,88 +88,36 @@ void WebAssemblyDAGToDAGISel::Select(SDN
uint64_t SyncScopeID =
cast<ConstantSDNode>(Node->getOperand(2).getNode())->getZExtValue();
+ MachineSDNode *Fence = nullptr;
switch (SyncScopeID) {
- case SyncScope::SingleThread: {
+ case SyncScope::SingleThread:
// We lower a single-thread fence to a pseudo compiler barrier instruction
// preventing instruction reordering. This will not be emitted in final
// binary.
- MachineSDNode *Fence =
- CurDAG->getMachineNode(WebAssembly::COMPILER_FENCE,
- DL, // debug loc
- MVT::Other, // outchain type
- Node->getOperand(0) // inchain
- );
- ReplaceNode(Node, Fence);
- CurDAG->RemoveDeadNode(Node);
- return;
- }
-
- case SyncScope::System: {
- // For non-emscripten systems, we have not decided on what we should
- // traslate fences to yet.
- if (!Subtarget->getTargetTriple().isOSEmscripten())
- report_fatal_error(
- "ATOMIC_FENCE is not yet supported in non-emscripten OSes");
-
- // Wasm does not have a fence instruction, but because all atomic
- // instructions in wasm are sequentially consistent, we translate a
- // fence to an idempotent atomic RMW instruction to a linear memory
- // address. All atomic instructions in wasm are sequentially consistent,
- // but this is to ensure a fence also prevents reordering of non-atomic
- // instructions in the VM. Even though LLVM IR's fence instruction does
- // not say anything about its relationship with non-atomic instructions,
- // we think this is more user-friendly.
- //
- // While any address can work, here we use a value stored in
- // __stack_pointer wasm global because there's high chance that area is
- // in cache.
- //
- // So the selected instructions will be in the form of:
- // %addr = get_global $__stack_pointer
- // %0 = i32.const 0
- // i32.atomic.rmw.or %addr, %0
- SDValue StackPtrSym = CurDAG->getTargetExternalSymbol(
- "__stack_pointer", TLI->getPointerTy(CurDAG->getDataLayout()));
- MachineSDNode *GetGlobal =
- CurDAG->getMachineNode(WebAssembly::GLOBAL_GET_I32, // opcode
- DL, // debug loc
- MVT::i32, // result type
- StackPtrSym // __stack_pointer symbol
- );
-
- SDValue Zero = CurDAG->getTargetConstant(0, DL, MVT::i32);
- auto *MMO = MF.getMachineMemOperand(
- MachinePointerInfo::getUnknownStack(MF),
- // FIXME Volatile isn't really correct, but currently all LLVM
- // atomic instructions are treated as volatiles in the backend, so
- // we should be consistent.
- MachineMemOperand::MOVolatile | MachineMemOperand::MOLoad |
- MachineMemOperand::MOStore,
- 4, 4, AAMDNodes(), nullptr, SyncScope::System,
- AtomicOrdering::SequentiallyConsistent);
- MachineSDNode *Const0 =
- CurDAG->getMachineNode(WebAssembly::CONST_I32, DL, MVT::i32, Zero);
- MachineSDNode *AtomicRMW = CurDAG->getMachineNode(
- WebAssembly::ATOMIC_RMW_OR_I32, // opcode
- DL, // debug loc
- MVT::i32, // result type
- MVT::Other, // outchain type
- {
- Zero, // alignment
- Zero, // offset
- SDValue(GetGlobal, 0), // __stack_pointer
- SDValue(Const0, 0), // OR with 0 to make it idempotent
- Node->getOperand(0) // inchain
- });
-
- CurDAG->setNodeMemRefs(AtomicRMW, {MMO});
- ReplaceUses(SDValue(Node, 0), SDValue(AtomicRMW, 1));
- CurDAG->RemoveDeadNode(Node);
- return;
- }
+ Fence = CurDAG->getMachineNode(WebAssembly::COMPILER_FENCE,
+ DL, // debug loc
+ MVT::Other, // outchain type
+ Node->getOperand(0) // inchain
+ );
+ break;
+ case SyncScope::System:
+ // Currently wasm only supports sequentially consistent atomics, so we
+ // always set the order to 0 (sequentially consistent).
+ Fence = CurDAG->getMachineNode(
+ WebAssembly::ATOMIC_FENCE,
+ DL, // debug loc
+ MVT::Other, // outchain type
+ CurDAG->getTargetConstant(0, DL, MVT::i32), // order
+ Node->getOperand(0) // inchain
+ );
+ break;
default:
llvm_unreachable("Unknown scope!");
}
+
+ ReplaceNode(Node, Fence);
+ CurDAG->RemoveDeadNode(Node);
+ return;
}
case ISD::GlobalTLSAddress: {
Modified: llvm/trunk/lib/Target/WebAssembly/WebAssemblyInstrAtomics.td
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/WebAssembly/WebAssemblyInstrAtomics.td?rev=370272&r1=370271&r2=370272&view=diff
==============================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssemblyInstrAtomics.td (original)
+++ llvm/trunk/lib/Target/WebAssembly/WebAssemblyInstrAtomics.td Wed Aug 28 16:13:43 2019
@@ -127,6 +127,19 @@ def : WaitPatGlobalAddrOffOnly<i64, int_
} // Predicates = [HasAtomics]
//===----------------------------------------------------------------------===//
+// Atomic fences
+//===----------------------------------------------------------------------===//
+
+// A compiler fence instruction that prevents reordering of instructions.
+let Defs = [ARGUMENTS] in {
+let isPseudo = 1, hasSideEffects = 1 in
+defm COMPILER_FENCE : ATOMIC_NRI<(outs), (ins), [], "compiler_fence">;
+let hasSideEffects = 1 in
+defm ATOMIC_FENCE : ATOMIC_NRI<(outs), (ins i8imm:$flags), [], "atomic.fence",
+ 0x03>;
+} // Defs = [ARGUMENTS]
+
+//===----------------------------------------------------------------------===//
// Atomic loads
//===----------------------------------------------------------------------===//
@@ -887,13 +900,3 @@ defm : TerRMWTruncExtPattern<
ATOMIC_RMW8_U_CMPXCHG_I32, ATOMIC_RMW16_U_CMPXCHG_I32,
ATOMIC_RMW8_U_CMPXCHG_I64, ATOMIC_RMW16_U_CMPXCHG_I64,
ATOMIC_RMW32_U_CMPXCHG_I64>;
-
-//===----------------------------------------------------------------------===//
-// Atomic fences
-//===----------------------------------------------------------------------===//
-
-// A compiler fence instruction that prevents reordering of instructions.
-let Defs = [ARGUMENTS] in {
-let isPseudo = 1, hasSideEffects = 1 in
-defm COMPILER_FENCE : ATOMIC_NRI<(outs), (ins), [], "compiler_fence">;
-} // Defs = [ARGUMENTS]
Modified: llvm/trunk/test/CodeGen/WebAssembly/atomic-fence.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/WebAssembly/atomic-fence.ll?rev=370272&r1=370271&r2=370272&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/WebAssembly/atomic-fence.ll (original)
+++ llvm/trunk/test/CodeGen/WebAssembly/atomic-fence.ll Wed Aug 28 16:13:43 2019
@@ -1,19 +1,12 @@
; RUN: llc < %s | FileCheck %s --check-prefix NOATOMIC
-; RUN: not llc < %s -mtriple=wasm32-unknown-unknown -mattr=+atomics,+sign-ext 2>&1 | FileCheck %s --check-prefixes NOEMSCRIPTEN
-; RUN: not llc < %s -mtriple=wasm32-unknown-wasi -mattr=+atomics,+sign-ext 2>&1 | FileCheck %s --check-prefixes NOEMSCRIPTEN
-; RUN: llc < %s -mtriple=wasm32-unknown-emscripten -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -mattr=+atomics,+sign-ext | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -wasm-disable-explicit-locals -wasm-keep-registers -mattr=+atomics | FileCheck %s
target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
target triple = "wasm32-unknown-unknown"
-; NOEMSCRIPTEN: LLVM ERROR: ATOMIC_FENCE is not yet supported in non-emscripten OSes
-
-; A multithread fence turns into 'global.get $__stack_pointer' followed by an
-; idempotent atomicrmw instruction.
+; A multithread fence is lowered to an atomic.fence instruction.
; CHECK-LABEL: multithread_fence:
-; CHECK: global.get $push[[SP:[0-9]+]]=, __stack_pointer
-; CHECK-NEXT: i32.const $push[[ZERO:[0-9]+]]=, 0
-; CHECK-NEXT: i32.atomic.rmw.or $drop=, 0($pop[[SP]]), $pop[[ZERO]]
+; CHECK: atomic.fence
; NOATOMIC-NOT: i32.atomic.rmw.or
define void @multithread_fence() {
fence seq_cst
@@ -23,10 +16,9 @@ define void @multithread_fence() {
; Fences with weaker memory orderings than seq_cst should be treated the same
; because atomic memory access in wasm are sequentially consistent.
; CHECK-LABEL: multithread_weak_fence:
-; CHECK: global.get $push{{.+}}=, __stack_pointer
-; CHECK: i32.atomic.rmw.or
-; CHECK: i32.atomic.rmw.or
-; CHECK: i32.atomic.rmw.or
+; CHECK: atomic.fence
+; CHECK-NEXT: atomic.fence
+; CHECK-NEXT: atomic.fence
define void @multithread_weak_fence() {
fence acquire
fence release
@@ -37,7 +29,8 @@ define void @multithread_weak_fence() {
; A singlethread fence becomes compiler_fence instruction, a pseudo instruction
; that acts as a compiler barrier. The barrier should not be emitted to .s file.
; CHECK-LABEL: singlethread_fence:
-; CHECK-NOT: compiler_fence
+; CHECK-NOT: compiler_fence
+; CHECK-NOT: atomic_fence
define void @singlethread_fence() {
fence syncscope("singlethread") seq_cst
fence syncscope("singlethread") acquire
Added: llvm/trunk/test/CodeGen/WebAssembly/atomic-fence.mir
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/WebAssembly/atomic-fence.mir?rev=370272&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/WebAssembly/atomic-fence.mir (added)
+++ llvm/trunk/test/CodeGen/WebAssembly/atomic-fence.mir Wed Aug 28 16:13:43 2019
@@ -0,0 +1,68 @@
+# RUN: llc -mtriple=wasm32-unknown-unknown -run-pass wasm-reg-stackify -run-pass wasm-explicit-locals %s -o - | FileCheck %s
+
+# In the two tests below, without compiler_fence or atomic.fence in between,
+# atomic.notify and i32.add will be reordered by register stackify pass to meet
+# 'call @foo''s requirements. But because we have fences between atomic.notify
+# and i32.add, they cannot be reordered, and local.set and local.get are
+# inserted to save and load atomic.notify's return value.
+
+--- |
+ target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+ target triple = "wasm32-unknown-unknown"
+
+ declare void @foo(i32, i32)
+ define void @compiler_fence_test(i32) {
+ ret void
+ }
+ define void @atomic_fence_test(i32) {
+ ret void
+ }
+...
+---
+# CHECK-LABEL: name: compiler_fence_test
+name: compiler_fence_test
+liveins:
+ - { reg: '$arguments' }
+tracksRegLiveness: true
+body: |
+ bb.0:
+ ; CHECK: %[[REG:[0-9]+]]:i32 = ATOMIC_NOTIFY
+ ; CHECK: LOCAL_SET_I32 [[LOCAL:[0-9]+]], %[[REG]]
+ ; CHECK: COMPILER_FENCE
+ ; CHECK: ADD_I32
+ ; CHECK: LOCAL_GET_I32 [[LOCAL]]
+ ; CHECK: CALL_VOID @foo
+
+ liveins: $arguments
+ %0:i32 = CONST_I32 0, implicit-def $arguments
+ %1:i32 = ATOMIC_NOTIFY 2, 0, %0:i32, %0:i32, implicit-def $arguments
+ COMPILER_FENCE implicit-def $arguments
+ %2:i32 = ADD_I32 %0:i32, %0:i32, implicit-def $arguments
+ CALL_VOID @foo, %2:i32, %1:i32, implicit-def $arguments
+ RETURN_VOID implicit-def $arguments
+...
+
+---
+# CHECK-LABEL: name: atomic_fence_test
+name: atomic_fence_test
+liveins:
+ - { reg: '$arguments' }
+tracksRegLiveness: true
+body: |
+ bb.0:
+ ; CHECK: %[[REG:[0-9]+]]:i32 = ATOMIC_NOTIFY
+ ; CHECK: LOCAL_SET_I32 [[LOCAL:[0-9]+]], %[[REG]]
+ ; CHECK: ATOMIC_FENCE
+ ; CHECK: ADD_I32
+ ; CHECK: LOCAL_GET_I32 [[LOCAL]]
+ ; CHECK: CALL_VOID @foo
+
+ liveins: $arguments
+ %0:i32 = CONST_I32 0, implicit-def $arguments
+ %1:i32 = ATOMIC_NOTIFY 2, 0, %0:i32, %0:i32, implicit-def $arguments
+ ATOMIC_FENCE 0, implicit-def $arguments
+ %2:i32 = ADD_I32 %0:i32, %0:i32, implicit-def $arguments
+ CALL_VOID @foo, %2:i32, %1:i32, implicit-def $arguments
+ RETURN_VOID implicit-def $arguments
+...
+
Modified: llvm/trunk/test/MC/WebAssembly/atomics-encodings.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/WebAssembly/atomics-encodings.s?rev=370272&r1=370271&r2=370272&view=diff
==============================================================================
--- llvm/trunk/test/MC/WebAssembly/atomics-encodings.s (original)
+++ llvm/trunk/test/MC/WebAssembly/atomics-encodings.s Wed Aug 28 16:13:43 2019
@@ -10,6 +10,9 @@ main:
# CHECK: i64.atomic.wait 0 # encoding: [0xfe,0x02,0x03,0x00]
i64.atomic.wait 0
+ # CHECK: atomic.fence # encoding: [0xfe,0x03,0x00]
+ atomic.fence
+
# CHECK: i32.atomic.load 0 # encoding: [0xfe,0x10,0x02,0x00]
i32.atomic.load 0
# CHECK: i64.atomic.load 4 # encoding: [0xfe,0x11,0x03,0x04]
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