Bug 1559965 - Wasm: Implement new atomic.fence instruction. r=bbouvier

This commit implements the 'atomic.fence' Wasm instruction.

Issue: WebAssembly/threads#140
Overview: WebAssembly/threads#141

The instruction is encoded as, 0xFE 0x03, with a reserved byte trailing for a future
memory order immediate. The instruction is implemented by emitting a memoryBarrier
through the macro assembler.

Differential Revision: https://phabricator.services.mozilla.com/D39264

UltraBlame original commit: d32c27f13f21b0927cbfb7ce6f8509c0dea6bf09

js/src/jit-test/tests/wasm/binary.js

@@ -3565,7 +3565,7 @@ for
 let
 i
 =
-3
+0x4
 ;
 i
 <

js/src/jit-test/tests/wasm/fence.js

@@ -0,0 +1,70 @@
+wasmFullPass
+(
+(
+module
+(
+func
+atomic
+.
+fence
+)
+(
+export
+"
+run
+"
+0
+)
+)
+)
+;
+wasmFullPass
+(
+(
+module
+(
+memory
+1
+)
+(
+func
+atomic
+.
+fence
+)
+(
+export
+"
+run
+"
+0
+)
+)
+)
+;
+wasmFullPass
+(
+(
+module
+(
+memory
+1
+1
+shared
+)
+(
+func
+atomic
+.
+fence
+)
+(
+export
+"
+run
+"
+0
+)
+)
+)
+;

js/src/jit/CodeGenerator.cpp

@@ -88089,6 +88089,35 @@ types
 )
 ;
 }
+void
+CodeGenerator
+:
+:
+visitWasmFence
+(
+LWasmFence
+*
+lir
+)
+{
+MOZ_ASSERT
+(
+gen
+-
+>
+compilingWasm
+(
+)
+)
+;
+masm
+.
+memoryBarrier
+(
+MembarFull
+)
+;
+}
 static_assert
 (
 !

js/src/jit/Lowering.cpp

@@ -36364,6 +36364,30 @@ TrueExprIndex
 )
 ;
 }
+void
+LIRGenerator
+:
+:
+visitWasmFence
+(
+MWasmFence
+*
+ins
+)
+{
+add
+(
+new
+(
+alloc
+(
+)
+)
+LWasmFence
+ins
+)
+;
+}
 static_assert
 (
 !

js/src/jit/MIR.h

@@ -55460,6 +55460,57 @@ WasmHeap
 }
 ;
 class
+MWasmFence
+:
+public
+MNullaryInstruction
+{
+protected
+:
+MWasmFence
+(
+)
+:
+MNullaryInstruction
+(
+classOpcode
+)
+{
+setGuard
+(
+)
+;
+}
+public
+:
+INSTRUCTION_HEADER
+(
+WasmFence
+)
+TRIVIAL_NEW_WRAPPERS
+AliasSet
+getAliasSet
+(
+)
+const
+override
+{
+return
+AliasSet
+:
+:
+None
+(
+)
+;
+}
+ALLOW_CLONE
+(
+MWasmFence
+)
+}
+;
+class
 MWasmCompareExchangeHeap
 :
 public

js/src/jit/shared/LIR-shared.h

@@ -34386,6 +34386,37 @@ toWasmCompareExchangeHeap
 }
 ;
 class
+LWasmFence
+:
+public
+LInstructionHelper
+<
+0
+0
+0
+>
+{
+public
+:
+LIR_HEADER
+(
+WasmFence
+)
+;
+explicit
+LWasmFence
+(
+)
+:
+LInstructionHelper
+(
+classOpcode
+)
+{
+}
+}
+;
+class
 LWasmAtomicExchangeHeap
 :
 public

js/src/wasm/WasmAST.h

@@ -2281,6 +2281,7 @@ UnaryOperator
 Unreachable
 Wait
 Wake
+Fence
 }
 ;
 class
@@ -4418,6 +4419,40 @@ count_
 }
 }
 ;
+struct
+AstFence
+:
+AstExpr
+{
+static
+const
+AstExprKind
+Kind
+=
+AstExprKind
+:
+:
+Fence
+;
+AstFence
+(
+)
+:
+AstExpr
+(
+AstExprKind
+:
+:
+Fence
+ExprType
+:
+:
+Void
+)
+{
+}
+}
+;
 class
 AstMemOrTableCopy
 :

js/src/wasm/WasmBaselineCompile.cpp

@@ -32990,6 +32990,12 @@ emitWake
 ;
 MOZ_MUST_USE
 bool
+emitFence
+(
+)
+;
+MOZ_MUST_USE
+bool
 emitAtomicXchg
 (
 ValType
@@ -48962,6 +48968,48 @@ bool
 BaseCompiler
 :
 :
+emitFence
+(
+)
+{
+if
+(
+!
+iter_
+.
+readFence
+(
+)
+)
+{
+return
+false
+;
+}
+if
+(
+deadCode_
+)
+{
+return
+true
+;
+}
+masm
+.
+memoryBarrier
+(
+MembarFull
+)
+;
+return
+true
+;
+}
+bool
+BaseCompiler
+:
+:
 bulkmemOpsEnabled
 (
 )
@@ -57329,6 +57377,22 @@ uint32_t
 ThreadOp
 :
 :
+Fence
+)
+:
+CHECK_NEXT
+(
+emitFence
+(
+)
+)
+;
+case
+uint32_t
+(
+ThreadOp
+:
+:
 I32AtomicLoad
 )
 :

js/src/wasm/WasmConstants.h

@@ -905,6 +905,9 @@ I32Wait
 I64Wait
 =
 0x02
+Fence
+=
+0x03
 I32AtomicLoad
 =
 0x10