[RISCV] Support .variant_cc directive for the assembler.

The patch is split from D103435. The patch supported a new directive .variant_cc
that annotates function with STO_RISCV_VARIANT_CC. Symbols marked with
STO_RISCV_VARIANT_CC do not use standard calling conversion or use parameter not
passed in GPR/FPR.

Related: riscv-non-isa/riscv-elf-psabi-doc#190

Initial authored by: HsiangKai

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D138352

Author: Yeting Kuo

llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp

@@ -180,6 +180,7 @@ class RISCVAsmParser : public MCTargetAsmParser {
   bool parseDirectiveOption();
   bool parseDirectiveAttribute();
   bool parseDirectiveInsn(SMLoc L);
+  bool parseDirectiveVariantCC();
 
   void setFeatureBits(uint64_t Feature, StringRef FeatureString) {
     if (!(getSTI().getFeatureBits()[Feature])) {
@@ -2035,6 +2036,8 @@ bool RISCVAsmParser::ParseDirective(AsmToken DirectiveID) {
     return parseDirectiveAttribute();
   if (IDVal == ".insn")
     return parseDirectiveInsn(DirectiveID.getLoc());
+  if (IDVal == ".variant_cc")
+    return parseDirectiveVariantCC();
 
   return true;
 }
@@ -2297,6 +2300,19 @@ bool RISCVAsmParser::parseDirectiveInsn(SMLoc L) {
                                  /*MatchingInlineAsm=*/false);
 }
 
+/// parseDirectiveVariantCC
+///  ::= .variant_cc symbol
+bool RISCVAsmParser::parseDirectiveVariantCC() {
+  StringRef Name;
+  if (getParser().parseIdentifier(Name))
+    return TokError("expected symbol name");
+  if (parseEOL())
+    return false;
+  getTargetStreamer().emitDirectiveVariantCC(
+      *getContext().getOrCreateSymbol(Name));
+  return false;
+}
+
 void RISCVAsmParser::emitToStreamer(MCStreamer &S, const MCInst &Inst) {
   MCInst CInst;
   bool Res = compressInst(CInst, Inst, getSTI(), S.getContext());

llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.cpp

@@ -187,6 +187,11 @@ void RISCVTargetELFStreamer::reset() {
   Contents.clear();
 }
 
+void RISCVTargetELFStreamer::emitDirectiveVariantCC(MCSymbol &Symbol) {
+  getStreamer().getAssembler().registerSymbol(Symbol);
+  cast<MCSymbolELF>(Symbol).setOther(ELF::STO_RISCV_VARIANT_CC);
+}
+
 namespace {
 class RISCVELFStreamer : public MCELFStreamer {
   static std::pair<unsigned, unsigned> getRelocPairForSize(unsigned Size) {

llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.h

@@ -106,6 +106,7 @@ class RISCVTargetELFStreamer : public RISCVTargetStreamer {
   void emitDirectiveOptionNoRVC() override;
   void emitDirectiveOptionRelax() override;
   void emitDirectiveOptionNoRelax() override;
+  void emitDirectiveVariantCC(MCSymbol &Symbol) override;
 
   void finish() override;
 };

llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp

@@ -32,6 +32,7 @@ void RISCVTargetStreamer::emitDirectiveOptionRVC() {}
 void RISCVTargetStreamer::emitDirectiveOptionNoRVC() {}
 void RISCVTargetStreamer::emitDirectiveOptionRelax() {}
 void RISCVTargetStreamer::emitDirectiveOptionNoRelax() {}
+void RISCVTargetStreamer::emitDirectiveVariantCC(MCSymbol &Symbol) {}
 void RISCVTargetStreamer::emitAttribute(unsigned Attribute, unsigned Value) {}
 void RISCVTargetStreamer::finishAttributeSection() {}
 void RISCVTargetStreamer::emitTextAttribute(unsigned Attribute,

llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.h

@@ -33,6 +33,7 @@ class RISCVTargetStreamer : public MCTargetStreamer {
   virtual void emitDirectiveOptionNoRVC();
   virtual void emitDirectiveOptionRelax();
   virtual void emitDirectiveOptionNoRelax();
+  virtual void emitDirectiveVariantCC(MCSymbol &Symbol);
   virtual void emitAttribute(unsigned Attribute, unsigned Value);
   virtual void finishAttributeSection();
   virtual void emitTextAttribute(unsigned Attribute, StringRef String);

llvm/test/MC/RISCV/directive-variant_cc.s

@@ -0,0 +1,42 @@
+// RUN: llvm-mc -triple riscv64 -filetype obj -o - %s | llvm-readobj --symbols - | FileCheck %s
+// RUN: llvm-mc -triple riscv64 -filetype obj -defsym=OBJ=1 -o - %s | llvm-readelf -s - | FileCheck %s --check-prefix=OBJ
+// RUN: not llvm-mc -triple riscv64 -filetype asm -defsym=ERR=1 -o - %s 2>&1 | FileCheck %s --check-prefix=ERR
+
+.text
+.variant_cc local
+local:
+
+// CHECK: Name: local
+// CHECK: Other [ (0x80)
+
+.ifdef OBJ
+/// Binding directive before .variant_cc.
+.global def1
+.variant_cc def1
+def1:
+
+/// Binding directive after .variant_cc.
+.variant_cc def2
+.weak def2
+def2:
+
+.globl alias_def1
+.set alias_def1, def1
+
+.variant_cc undef
+
+// OBJ:      NOTYPE LOCAL  DEFAULT [VARIANT_CC] [[#]] local
+// OBJ-NEXT: NOTYPE GLOBAL DEFAULT [VARIANT_CC] [[#]] def1
+// OBJ-NEXT: NOTYPE WEAK   DEFAULT [VARIANT_CC] [[#]] def2
+// OBJ-NEXT: NOTYPE GLOBAL DEFAULT              [[#]] alias_def1
+// OBJ-NEXT: NOTYPE GLOBAL DEFAULT [VARIANT_CC] UND   undef
+.endif
+
+.ifdef ERR
+.variant_cc
+// ERR: [[#@LINE-1]]:12: error: expected symbol name
+
+.global fox
+.variant_cc fox bar
+// ERR: [[#@LINE-1]]:17: error: expected newline
+.endif