[X86] Add support for vex, vex2, vex3, and evex for MASM

For MASM syntax, the prefixes are not enclosed in braces.
The assembly code should like:
  "evex vcvtps2pd xmm0, xmm1"

Differential Revision: https://reviews.llvm.org/D90441

clang/lib/AST/Stmt.cpp

@@ -791,7 +791,27 @@ std::string GCCAsmStmt::generateAsmString(const ASTContext &C) const {
 /// Assemble final IR asm string (MS-style).
 std::string MSAsmStmt::generateAsmString(const ASTContext &C) const {
   // FIXME: This needs to be translated into the IR string representation.
-  return std::string(AsmStr);
+  SmallVector<StringRef, 8> Pieces;
+  AsmStr.split(Pieces, "\n\t");
+  std::string MSAsmString;
+  for (size_t I = 0, E = Pieces.size(); I < E; ++I) {
+    StringRef Instruction = Pieces[I];
+    // For vex/vex2/vex3/evex masm style prefix, convert it to att style
+    // since we don't support masm style prefix in backend.
+    if (Instruction.startswith("vex "))
+      MSAsmString += '{' + Instruction.substr(0, 3).str() + '}' +
+                     Instruction.substr(3).str();
+    else if (Instruction.startswith("vex2 ") ||
+             Instruction.startswith("vex3 ") || Instruction.startswith("evex "))
+      MSAsmString += '{' + Instruction.substr(0, 4).str() + '}' +
+                     Instruction.substr(4).str();
+    else
+      MSAsmString += Instruction.str();
+    // If this is not the last instruction, adding back the '\n\t'.
+    if (I < E - 1)
+      MSAsmString += "\n\t";
+  }
+  return MSAsmString;
 }
 
 Expr *MSAsmStmt::getOutputExpr(unsigned i) {

clang/test/CodeGen/X86/ms-inline-asm-prefix.c

@@ -0,0 +1,14 @@
+// REQUIRES: x86-registered-target
+// RUN:%clang_cc1 %s -ferror-limit 0 -triple=x86_64-pc-windows-msvc -target-feature +avx512f -target-feature +avx2 -target-feature +avx512vl -fasm-blocks -mllvm -x86-asm-syntax=intel -S -emit-llvm -o -  | FileCheck %s -check-prefix=INTEL
+// RUN:%clang_cc1 %s -ferror-limit 0 -triple=x86_64-pc-windows-msvc -target-feature +avx512f -target-feature +avx2 -target-feature +avx512vl -fasm-blocks -mllvm -x86-asm-syntax=att -S -emit-llvm -o -  | FileCheck %s -check-prefix=ATT
+
+void check_inline_prefix(void) {
+  __asm {
+    // INTEL: call void asm sideeffect inteldialect "{vex} vcvtps2pd xmm0, xmm1\0A\09{vex2} vcvtps2pd xmm0, xmm1\0A\09{vex3} vcvtps2pd xmm0, xmm1\0A\09{evex} vcvtps2pd xmm0, xmm1", "~{xmm0},~{dirflag},~{fpsr},~{flags}"()
+    // ATT: call void asm sideeffect inteldialect "{vex} vcvtps2pd xmm0, xmm1\0A\09{vex2} vcvtps2pd xmm0, xmm1\0A\09{vex3} vcvtps2pd xmm0, xmm1\0A\09{evex} vcvtps2pd xmm0, xmm1", "~{xmm0},~{dirflag},~{fpsr},~{flags}"()
+    vex vcvtps2pd xmm0, xmm1
+    vex2 vcvtps2pd xmm0, xmm1
+    vex3 vcvtps2pd xmm0, xmm1
+    evex vcvtps2pd xmm0, xmm1
+  }
+}

llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp

@@ -3064,7 +3064,26 @@ bool X86AsmParser::ParseInstruction(ParseInstructionInfo &Info, StringRef Name,
       }
       continue;
     }
+    // Parse MASM style pseudo prefixes.
+    if (isParsingMSInlineAsm()) {
+      if (Name.equals_lower("vex"))
+        ForcedVEXEncoding = VEXEncoding_VEX;
+      else if (Name.equals_lower("vex2"))
+        ForcedVEXEncoding = VEXEncoding_VEX2;
+      else if (Name.equals_lower("vex3"))
+        ForcedVEXEncoding = VEXEncoding_VEX3;
+      else if (Name.equals_lower("evex"))
+        ForcedVEXEncoding = VEXEncoding_EVEX;
 
+      if (ForcedVEXEncoding != VEXEncoding_Default) {
+        if (getLexer().isNot(AsmToken::Identifier))
+          return Error(Parser.getTok().getLoc(), "Expected identifier");
+        // FIXME: The mnemonic won't match correctly if its not in lower case.
+        Name = Parser.getTok().getString();
+        NameLoc = Parser.getTok().getLoc();
+        Parser.Lex();
+      }
+    }
     break;
   }
 
@@ -4370,10 +4389,16 @@ bool X86AsmParser::MatchAndEmitIntelInstruction(SMLoc IDLoc, unsigned &Opcode,
 
   MCInst Inst;
 
-  // If VEX3 encoding is forced, we need to pass the USE_VEX3 flag to the
-  // encoder.
-  if (ForcedVEXEncoding == VEXEncoding_VEX3)
+  // If VEX/EVEX encoding is forced, we need to pass the USE_* flag to the
+  // encoder and printer.
+  if (ForcedVEXEncoding == VEXEncoding_VEX)
+    Prefixes |= X86::IP_USE_VEX;
+  else if (ForcedVEXEncoding == VEXEncoding_VEX2)
+    Prefixes |= X86::IP_USE_VEX2;
+  else if (ForcedVEXEncoding == VEXEncoding_VEX3)
     Prefixes |= X86::IP_USE_VEX3;
+  else if (ForcedVEXEncoding == VEXEncoding_EVEX)
+    Prefixes |= X86::IP_USE_EVEX;
 
   // Set encoded flags for {disp8} and {disp32}.
   if (ForcedDispEncoding == DispEncoding_Disp8)