Index: lib/Target/X86/AsmParser/X86AsmParser.cpp =================================================================== --- lib/Target/X86/AsmParser/X86AsmParser.cpp +++ lib/Target/X86/AsmParser/X86AsmParser.cpp @@ -2457,11 +2457,21 @@ Operands.push_back(X86Operand::CreateToken(PatchedName, NameLoc)); // Determine whether this is an instruction prefix. - bool isPrefix = - Name == "lock" || Name == "rep" || - Name == "repe" || Name == "repz" || - Name == "repne" || Name == "repnz" || - Name == "rex64" || Name == "data16" || Name == "data32"; + // FIXME: + // Enhance prefixes integrity robustness. for example, following forms + // are currently tolerated: + // repz repnz ; GAS errors for the use of two similar prefixes + // lock addq %rax, %rbx ; Destination operand must be of memory type + // xacquire ; xacquire must be accompanied by 'lock' + bool isPrefix = StringSwitch(Name) + .Cases("data32", "lock", + "rep", "repe", + "repz", "repne", + "repnz", "rex64", + "data16", true) + .Cases("xacquire", "xrelease", true) + .Cases("acquire", "release", isParsingIntelSyntax()) + .Default(false); bool CurlyAsEndOfStatement = false; // This does the actual operand parsing. Don't parse any more if we have a Index: lib/Target/X86/X86InstrInfo.td =================================================================== --- lib/Target/X86/X86InstrInfo.td +++ lib/Target/X86/X86InstrInfo.td @@ -2848,6 +2848,10 @@ def : MnemonicAlias<"ud2a", "ud2", "att">; def : MnemonicAlias<"verrw", "verr", "att">; +// MS recognizes 'xacquire'/'xrelease' as 'acquire'/'release' +def : MnemonicAlias<"acquire", "xacquire", "intel">; +def : MnemonicAlias<"release", "xrelease", "intel">; + // System instruction aliases. def : MnemonicAlias<"iret", "iretw", "att">, Requires<[In16BitMode]>; def : MnemonicAlias<"iret", "iretl", "att">, Requires<[Not16BitMode]>; Index: test/MC/X86/x86-64.s =================================================================== --- test/MC/X86/x86-64.s +++ test/MC/X86/x86-64.s @@ -930,6 +930,21 @@ // CHECK: xorq %rsi, (%rdi) // CHECK: encoding: [0x48,0x31,0x37] +xacquire lock addq %rax, (%rax) +// CHECK: xacquire +// CHECK: encoding: [0xf2] +// CHECK: lock +// CHECK: encoding: [0xf0] +// CHECK: addq %rax, (%rax) +// CHECK: encoding: [0x48,0x01,0x00] + +xrelease lock addq %rax, (%rax) +// CHECK: xrelease +// CHECK: encoding: [0xf3] +// CHECK: lock +// CHECK: encoding: [0xf0] +// CHECK: addq %rax, (%rax) +// CHECK: encoding: [0x48,0x01,0x00] // rdar://8033482 rep movsl