Reland "[AsmParser] make .ascii support spaces as separators"

This relands commit e0963ae, which was
reverted on commit 82c4153 due to a
test failure, which turned out to be a false positive.

Author: jcai19

llvm/lib/MC/MCParser/AsmParser.cpp

@@ -3008,13 +3008,20 @@ bool AsmParser::parseAngleBracketString(std::string &Data) {
 }
 
 /// parseDirectiveAscii:
-///   ::= ( .ascii | .asciz | .string ) [ "string" ( , "string" )* ]
+//    ::= .ascii [ "string"+ ( , "string"+ )* ]
+///   ::= ( .asciz | .string ) [ "string" ( , "string" )* ]
 bool AsmParser::parseDirectiveAscii(StringRef IDVal, bool ZeroTerminated) {
   auto parseOp = [&]() -> bool {
     std::string Data;
-    if (checkForValidSection() || parseEscapedString(Data))
+    if (checkForValidSection())
       return true;
-    getStreamer().emitBytes(Data);
+    // Only support spaces as separators for .ascii directive for now. See the
+    // discusssion at https://reviews.llvm.org/D91460 for more details.
+    do {
+      if (parseEscapedString(Data))
+        return true;
+      getStreamer().emitBytes(Data);
+    } while (!ZeroTerminated && getTok().is(AsmToken::String));
     if (ZeroTerminated)
       getStreamer().emitBytes(StringRef("\0", 1));
     return false;

llvm/test/MC/AsmParser/directive_ascii.s

@@ -48,3 +48,11 @@ TEST6:
 TEST7:
         .ascii "\x64\Xa6B"
         .ascii "\xface\x0Fe"
+
+# CHECK-LABEL: TEST8:
+# CHECK-NEXT: .byte 65
+# CHECK-NEXT: .byte 66
+# CHECK-NEXT: .byte 67
+# CHECK-NEXT: .byte 68
+TEST8:
+        .ascii "A", "B" "C", "D"