[X86] Allow usage of prefixes as a separate instr

[avt77]

Summary

After r315899 we removed a possibility to use prefixes as separate x86 intsrs but there are code pieces using such a possibility. This patch returns this thing: if some coder uses end-of-statement after a prefix (semicolon, comment, etc.) then we treat this prefix as a standalone intruction.

[dim]

LGTM, works for all my test cases.

lib/Target/X86/AsmParser/X86AsmParser.cpp

bool X86AsmParser::ParseInstruction(ParseInstructionInfo &Info, StringRef Name,
   while (isLockRepeatPrefix(Name.lower())) {
     unsigned Prefix =
         StringSwitch<unsigned>(Name)
             .Cases("lock", "lock", X86::IP_HAS_LOCK)
             .Cases("rep", "repe", "repz", X86::IP_HAS_REPEAT)
             .Cases("repne", "repnz", X86::IP_HAS_REPEAT_NE)
             .Default(X86::IP_NO_PREFIX); // Invalid prefix (impossible)
     Flags |= Prefix;
+    if (getLexer().is(AsmToken::EndOfStatement)) {
+      // We don't have real instr with the given prefix
+      //  let's use the prefix as the instr.
+      // TODO: there could be several prefixes one after another
+      Flags = X86::IP_NO_PREFIX;
+      break;
+    }
     Name = Parser.getTok().getString();
     Parser.Lex(); // eat the prefix
     // Hack: we could have something like "rep # some comment" or
     //    "lock; cmpxchg16b $1" or "lock\0A\09incl" or "lock/incl"
     while (Name.startswith(";") || Name.startswith("\n") ||
            Name.startswith("#") || Name.startswith("\t") ||
            Name.startswith("/")) {
       Name = Parser.getTok().getString();

test/CodeGen/X86/inline-asm-A-constraint.ll

entry:
   %2 = tail call i128 asm sideeffect "lock; cmpxchg16b $1", "=A,=*m,{cx},{bx},0,*m,~{dirflag},~{fpsr},~{flags}"(i8* %ptr, i64 %conv, i64 %conv1, i128 %1, i8* %ptr) #1, !srcloc !5
   %retval.sroa.0.0.extract.trunc = trunc i128 %2 to i64
   %retval.sroa.2.0.extract.shift = lshr i128 %2, 64
   %retval.sroa.2.0.extract.trunc = trunc i128 %retval.sroa.2.0.extract.shift to i64
   %.fca.0.insert = insertvalue { i64, i64 } undef, i64 %retval.sroa.0.0.extract.trunc, 0
   %.fca.1.insert = insertvalue { i64, i64 } %.fca.0.insert, i64 %retval.sroa.2.0.extract.trunc, 1
   ret { i64, i64 } %.fca.1.insert
 }
-; CHECK: lock cmpxchg16b
+; CHECK: lock
+; CHECK-NEXT: cmpxchg16b
 
 attributes #0 = { nounwind uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
 attributes #1 = { nounwind }
 
 !llvm.ident = !{!0}
 
 !0 = !{!"clang version 5.0.0 (trunk 300088)"}
 !1 = !{!2, !2, i64 0}
 !2 = !{!"__int128", !3, i64 0}
 !3 = !{!"omnipotent char", !4, i64 0}
 !4 = !{!"Simple C/C++ TBAA"}
 !5 = !{i32 269}

test/MC/X86/x86-64.s

// CHECK: shldl %cl, %eax, %ebx
         shldl %cl, %eax, %ebx
 
 // CHECK: shll $2, %eax
         shll $2, %eax
 
 // CHECK: shll $2, %eax
         sall $2, %eax
 
-// CHECK: rep movsb
+// CHECK: rep
+// CHECK-NEXT: movsb
 rep     # comment
 movsb
 
 // CHECK: rep
 // CHECK: insb
         rep;insb
 
 // CHECK: rep

 
 // CHECK: ptwriteq 3735928559(%rbx,%rcx,8)
 // CHECK:  encoding: [0xf3,0x48,0x0f,0xae,0xa4,0xcb,0xef,0xbe,0xad,0xde]
 ptwriteq 0xdeadbeef(%rbx,%rcx,8)
 
 // CHECK: ptwriteq %rax
 // CHECK:  encoding: [0xf3,0x48,0x0f,0xae,0xe0]
 ptwriteq %rax
+
+//  __asm __volatile(
+//    "pushf        \n\t"
+//    "popf       \n\t"
+//    "rep        \n\t"
+//    ".byte  0x0f, 0xa7, 0xd0"
+//  );
+// CHECK: pushfq
+// CHECK-NEXT: popfq
+// CHECK-NEXT: rep
+// CHECK-NEXT: .byte 15
+// CHECK-NEXT: .byte 167
+// CHECK-NEXT: .byte 208
+pushfq
+popfq
+rep
+.byte 15
+.byte 167
+.byte 208
+
+// CHECK: lock
+// CHECK: cmpxchgl
+        cmp $0, %edx
+        je 1f
+        lock
+1:      cmpxchgl %ecx,(%rdi)
+
+// CHECK: rep
+// CHECK-NEXT: byte
+rep
+.byte 0xa4      # movsb
+
+// CHECK: lock
+// This line has to be the last one in the file
+lock