[RISCV] Add support for custom CSRs for Sifive S76.

Support for below CSRs is addeed -
1. Branch Prediction Mode CSR
2. Feature Disable CSR
3. Power Dial CSR
4. RNMI CSRs

spec:https://sifive.cdn.prismic.io/sifive/767804da-53b2-4893-97d5-b7c030ae0a94_s76mc_core_complex_manual_21G3.pdf

This patch removes AltName field from SysReg class because we are now using
separate class for custom vendor CSRs. Also, all use of AltName have been changed
to DeprecatedName because both were interchangeably used for old names which are
not in use in latest RISCV spec.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D153499

Author: quic-garvgupt

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

@@ -1803,18 +1803,57 @@ ParseStatus RISCVAsmParser::parseCSRSystemRegister(OperandVector &Operands) {
     if (getParser().parseIdentifier(Identifier))
       return ParseStatus::Failure;
 
+    // Check for CSR names conflicts.
+    // Custom CSR names might conflict with CSR names in privileged spec.
+    // E.g. - SiFive mnscratch(0x350) and privileged spec mnscratch(0x740).
+    auto CheckCSRNameConflict = [&]() {
+      if (!(RISCVSysReg::lookupSysRegByName(Identifier))) {
+        Error(S, "system register use requires an option to be enabled");
+        return true;
+      }
+      return false;
+    };
+
+    // First check for vendor specific CSRs.
+    auto SiFiveReg = RISCVSysReg::lookupSiFiveRegByName(Identifier);
+    if (SiFiveReg) {
+      if (SiFiveReg->haveVendorRequiredFeatures(getSTI().getFeatureBits())) {
+        Operands.push_back(
+            RISCVOperand::createSysReg(Identifier, S, SiFiveReg->Encoding));
+        return ParseStatus::Success;
+      }
+      if (CheckCSRNameConflict())
+        return ParseStatus::Failure;
+    }
+
     auto SysReg = RISCVSysReg::lookupSysRegByName(Identifier);
-    if (!SysReg)
-      SysReg = RISCVSysReg::lookupSysRegByAltName(Identifier);
     if (!SysReg)
       if ((SysReg = RISCVSysReg::lookupSysRegByDeprecatedName(Identifier)))
         Warning(S, "'" + Identifier + "' is a deprecated alias for '" +
                        SysReg->Name + "'");
 
-    // Accept a named Sys Reg if the required features are present.
+    // Check for CSR encoding conflicts.
+    // Custom CSR encoding might conflict with CSR encoding in privileged spec.
+    // E.g. - SiFive mnscratch(0x350) and privileged spec miselect(0x350).
+    auto CheckCSREncodingConflict = [&]() {
+      auto Reg = RISCVSysReg::lookupSiFiveRegByEncoding(SysReg->Encoding);
+      if (Reg && Reg->haveVendorRequiredFeatures(getSTI().getFeatureBits())) {
+        Warning(S, "'" + Identifier + "' CSR is not available on the current " +
+                       "subtarget. Instead '" + Reg->Name +
+                       "' CSR will be used.");
+        Operands.push_back(
+            RISCVOperand::createSysReg(Reg->Name, S, Reg->Encoding));
+        return true;
+      }
+      return false;
+    };
+
+    // Accept a named SysReg if the required features are present.
     if (SysReg) {
       if (!SysReg->haveRequiredFeatures(getSTI().getFeatureBits()))
         return Error(S, "system register use requires an option to be enabled");
+      if (CheckCSREncodingConflict())
+        return ParseStatus::Success;
       Operands.push_back(
           RISCVOperand::createSysReg(Identifier, S, SysReg->Encoding));
       return ParseStatus::Success;

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

@@ -27,6 +27,7 @@ extern const SubtargetFeatureKV RISCVFeatureKV[RISCV::NumSubtargetFeatures];
 
 namespace RISCVSysReg {
 #define GET_SysRegsList_IMPL
+#define GET_SiFiveRegsList_IMPL
 #include "RISCVGenSearchableTables.inc"
 } // namespace RISCVSysReg
 

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

@@ -363,7 +363,6 @@ int getLoadFPImm(APFloat FPImm);
 namespace RISCVSysReg {
 struct SysReg {
   const char *Name;
-  const char *AltName;
   const char *DeprecatedName;
   unsigned Encoding;
   // FIXME: add these additional fields when needed.
@@ -387,9 +386,22 @@ struct SysReg {
       return true;
     return (FeaturesRequired & ActiveFeatures) == FeaturesRequired;
   }
+
+  bool haveVendorRequiredFeatures(const FeatureBitset &ActiveFeatures) const {
+    // Not in 32-bit mode.
+    if (isRV32Only && ActiveFeatures[RISCV::Feature64Bit])
+      return false;
+    // No required feature associated with the system register.
+    if (FeaturesRequired.none())
+      return false;
+    return (FeaturesRequired & ActiveFeatures) == FeaturesRequired;
+  }
 };
 
+struct SiFiveReg : SysReg {};
+
 #define GET_SysRegsList_DECL
+#define GET_SiFiveRegsList_DECL
 #include "RISCVGenSearchableTables.inc"
 } // end namespace RISCVSysReg
 

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

@@ -120,8 +120,11 @@ void RISCVInstPrinter::printCSRSystemRegister(const MCInst *MI, unsigned OpNo,
                                               const MCSubtargetInfo &STI,
                                               raw_ostream &O) {
   unsigned Imm = MI->getOperand(OpNo).getImm();
+  auto SiFiveReg = RISCVSysReg::lookupSiFiveRegByEncoding(Imm);
   auto SysReg = RISCVSysReg::lookupSysRegByEncoding(Imm);
-  if (SysReg && SysReg->haveRequiredFeatures(STI.getFeatureBits()))
+  if (SiFiveReg && SiFiveReg->haveVendorRequiredFeatures(STI.getFeatureBits()))
+    O << SiFiveReg->Name;
+  else if (SysReg && SysReg->haveRequiredFeatures(STI.getFeatureBits()))
     O << SysReg->Name;
   else
     O << Imm;

llvm/lib/Target/RISCV/RISCVSystemOperands.td

@@ -19,11 +19,9 @@ include "llvm/TableGen/SearchableTable.td"
 
 class SysReg<string name, bits<12> op> {
   string Name = name;
-  // A maximum of one alias is supported right now.
-  string AltName = name;
-  // A maximum of one deprecated name is supported right now.  Unlike the
-  // `AltName` alias, a `DeprecatedName` generates a diagnostic when the name is
-  // used to encourage software to migrate away from the name.
+  // A maximum of one deprecated name is supported right now. It generates a
+  // diagnostic when the name is used to encourage software to migrate away from
+  // the name.
   string DeprecatedName = "";
   bits<12> Encoding = op;
   // FIXME: add these additional fields when needed.
@@ -43,7 +41,7 @@ def SysRegsList : GenericTable {
   let FilterClass = "SysReg";
   // FIXME: add "ReadWrite", "Mode", "Extra", "Number" fields when needed.
   let Fields = [
-    "Name", "AltName", "DeprecatedName", "Encoding", "FeaturesRequired",
+    "Name", "DeprecatedName", "Encoding", "FeaturesRequired",
     "isRV32Only",
   ];
 
@@ -56,13 +54,32 @@ def lookupSysRegByName : SearchIndex {
   let Key = [ "Name" ];
 }
 
-def lookupSysRegByAltName : SearchIndex {
+def lookupSysRegByDeprecatedName : SearchIndex {
   let Table = SysRegsList;
-  let Key = [ "AltName" ];
+  let Key = [ "DeprecatedName" ];
 }
 
-def lookupSysRegByDeprecatedName : SearchIndex {
-  let Table = SysRegsList;
+class SiFiveReg<string name, bits<12> op> : SysReg<name, op>;
+
+def SiFiveRegsList : GenericTable {
+  let FilterClass = "SiFiveReg";
+  // FIXME: add "ReadWrite", "Mode", "Extra", "Number" fields when needed.
+  let Fields = [
+    "Name", "DeprecatedName", "Encoding", "FeaturesRequired",
+    "isRV32Only",
+  ];
+
+  let PrimaryKey = [ "Encoding" ];
+  let PrimaryKeyName = "lookupSiFiveRegByEncoding";
+}
+
+def lookupSiFiveRegByName : SearchIndex {
+  let Table = SiFiveRegsList;
+  let Key = [ "Name" ];
+}
+
+def lookupSiFiveRegByDeprecatedName : SearchIndex {
+  let Table = SiFiveRegsList;
   let Key = [ "DeprecatedName" ];
 }
 
@@ -292,7 +309,7 @@ foreach i = 3...31 in
 //===----------------------------------------------------------------------===//
 // Machine Counter Setup
 //===----------------------------------------------------------------------===//
-let AltName = "mucounteren" in // Privileged spec v1.9.1 Name
+let DeprecatedName = "mucounteren" in // Privileged spec v1.9.1 Name
 def : SysReg<"mcountinhibit", 0x320>;
 
 // mhpmevent3-mhpmevent31 at 0x323-0x33F.
@@ -305,6 +322,20 @@ foreach i = 3...31 in {
   def : SysReg<"mhpmevent"#i#"h", !add(0x723, !sub(i, 3))>;
 }
 
+//===----------------------------------------------------------------------===//
+// SiFive Custom Machine Mode Registers
+//===----------------------------------------------------------------------===//
+
+let FeaturesRequired = [{ {RISCV::FeatureVendorXSfcie} }] in {
+def : SiFiveReg<"mnscratch", 0x350>;
+def : SiFiveReg<"mnepc", 0x351>;
+def : SiFiveReg<"mncause", 0x352>;
+def : SiFiveReg<"mnstatus", 0x353>;
+def : SiFiveReg<"mbpm", 0x7C0>;
+def : SiFiveReg<"mfd", 0x7C1>;
+def : SiFiveReg<"mpd", 0x7C8>;
+}
+
 //===----------------------------------------------------------------------===//
 // Debug/ Trace Registers (shared with Debug Mode)
 //===----------------------------------------------------------------------===//
@@ -322,7 +353,7 @@ def : SysReg<"dpc", 0x7B1>;
 
 // "dscratch" is an alternative name for "dscratch0" which appeared in earlier
 // drafts of the RISC-V debug spec
-let AltName = "dscratch" in
+let DeprecatedName = "dscratch" in
 def : SysReg<"dscratch0", 0x7B2>;
 def : SysReg<"dscratch1", 0x7B3>;
 

llvm/test/MC/RISCV/machine-csr-names.s

@@ -9,6 +9,9 @@
 # RUN: llvm-mc -filetype=obj -triple riscv64 < %s \
 # RUN:     | llvm-objdump -d - \
 # RUN:     | FileCheck -check-prefix=CHECK-INST-ALIAS %s
+#
+# RUN: llvm-mc -triple riscv32 %s 2>&1 | FileCheck -check-prefix CHECK-WARN %s
+# RUN: llvm-mc -triple riscv64 %s 2>&1 | FileCheck -check-prefix CHECK-WARN %s
 
 ##################################
 # Machine Information Registers
@@ -1492,6 +1495,8 @@ csrrs t1, dscratch, zero
 # uimm12
 csrrs t2, 0x7B2, zero
 
+# CHECK-WARN: warning: 'dscratch' is a deprecated alias for 'dscratch0'
+
 # dscratch1
 # name
 # CHECK-INST: csrrs t1, dscratch1, zero
@@ -1944,6 +1949,8 @@ csrrs t1, mucounteren, zero
 # uimm12
 csrrs t2, 0x320, zero
 
+# CHECK-WARN: warning: 'mucounteren' is a deprecated alias for 'mcountinhibit'
+
 # mhpmevent3
 # name
 # CHECK-INST: csrrs t1, mhpmevent3, zero

llvm/test/MC/RISCV/xsfcie-invalid.s

@@ -23,3 +23,17 @@ cease x1 # CHECK: :[[@LINE]]:7: error: invalid operand for instruction
 cease 0x10 # CHECK: :[[@LINE]]:7: error: invalid operand for instruction
 
 cease # CHECK: :[[@LINE]]:1: error: instruction requires the following: 'XSfcie' (SiFive Custom Instruction Extension SCIE.)
+
+csrr t1, mbpm # CHECK: :[[@LINE]]:10: error: system register use requires an option to be enabled
+
+csrr t1, mfd # CHECK: :[[@LINE]]:10: error: system register use requires an option to be enabled
+
+csrr t1, mpd # CHECK: :[[@LINE]]:10: error: system register use requires an option to be enabled
+
+csrr t1, mnscratch # CHECK: :[[@LINE]]:10: error: system register use requires an option to be enabled
+
+csrr t1, mnepc # CHECK: :[[@LINE]]:10: error: system register use requires an option to be enabled
+
+csrr t1, mncause # CHECK: :[[@LINE]]:10: error: system register use requires an option to be enabled
+
+csrr t1, mnstatus # CHECK: :[[@LINE]]:10: error: system register use requires an option to be enabled

llvm/test/MC/RISCV/xsfcie-valid.s

@@ -3,6 +3,10 @@
 # RUN:     | FileCheck -check-prefixes=CHECK-ENC,CHECK-INST %s
 # RUN: llvm-mc %s -triple=riscv64 -mattr=+xsfcie -riscv-no-aliases -show-encoding \
 # RUN:     | FileCheck -check-prefixes=CHECK-ENC,CHECK-INST %s
+# RUN: llvm-mc %s -triple=riscv32 -mattr=+xsfcie -riscv-no-aliases -show-encoding 2>&1 \
+# RUN:     | FileCheck -check-prefixes=CHECK-WARN %s
+# RUN: llvm-mc %s -triple=riscv64 -mattr=+xsfcie -riscv-no-aliases -show-encoding 2>&1 \
+# RUN:     | FileCheck -check-prefixes=CHECK-WARN %s
 # RUN: llvm-mc -filetype=obj -triple riscv32 -mattr=+xsfcie < %s \
 # RUN:     | llvm-objdump --mattr=+xsfcie -M no-aliases -d - \
 # RUN:     | FileCheck -check-prefix=CHECK-INST %s
@@ -11,6 +15,8 @@
 # RUN:     | FileCheck -check-prefix=CHECK-INST %s
 # RUN: llvm-mc %s -triple=riscv64 -mcpu=sifive-s76 -riscv-no-aliases -show-encoding \
 # RUN:     | FileCheck -check-prefixes=CHECK-ENC,CHECK-INST %s
+# RUN: llvm-mc %s -triple=riscv64 -mcpu=sifive-s76 -riscv-no-aliases -show-encoding 2>&1 \
+# RUN:     | FileCheck -check-prefixes=CHECK-WARN %s
 # RUN: llvm-mc -filetype=obj -triple riscv64 -mcpu=sifive-s76 < %s \
 # RUN:     | llvm-objdump --mcpu=sifive-s76 -M no-aliases -d - \
 # RUN:     | FileCheck -check-prefix=CHECK-INST %s
@@ -40,3 +46,91 @@ cdiscard.d.l1 x7
 # CHECK-INST: cease
 # CHECK-ENC: encoding: [0x73,0x00,0x50,0x30]
 cease
+
+# mbpm
+# name
+# CHECK-INST: csrrs t2, mbpm, zero
+# CHECK-ENC: encoding: [0xf3,0x23,0x00,0x7c]
+# uimm12
+# CHECK-INST: csrrs t2, mbpm, zero
+# CHECK-ENC: encoding: [0xf3,0x23,0x00,0x7c]
+# name
+csrrs t2, mbpm, zero
+# uimm12
+csrrs t2, 0x7C0, zero
+
+# mfd
+# name
+# CHECK-INST: csrrs t2, mfd, zero
+# CHECK-ENC: encoding: [0xf3,0x23,0x10,0x7c]
+# uimm12
+# CHECK-INST: csrrs t2, mfd, zero
+# CHECK-ENC: encoding: [0xf3,0x23,0x10,0x7c]
+# name
+csrrs t2, mfd, zero
+# uimm12
+csrrs t2, 0x7C1, zero
+
+# mpd
+# name
+# CHECK-INST: csrrs t2, mpd, zero
+# CHECK-ENC: encoding: [0xf3,0x23,0x80,0x7c]
+# uimm12
+# CHECK-INST: csrrs t2, mpd, zero
+# CHECK-ENC: encoding: [0xf3,0x23,0x80,0x7c]
+# name
+csrrs t2, mpd, zero
+# uimm12
+csrrs t2, 0x7C8, zero
+
+# mnscratch
+# name
+# CHECK-INST: csrrs t1, mnscratch, zero
+# CHECK-ENC: encoding: [0x73,0x23,0x00,0x35]
+# CHECK-WARN: warning: 'miselect' CSR is not available on the current subtarget. Instead 'mnscratch' CSR will be used.
+# uimm12
+# CHECK-INST: csrrs t2, mnscratch, zero
+# CHECK-ENC: encoding: [0xf3,0x23,0x00,0x35]
+# name
+csrrs t1, mnscratch, zero
+csrrs t1, miselect, zero
+# uimm12
+csrrs t2, 0x350, zero
+
+# mnepc
+# name
+# CHECK-INST: csrrs t1, mnepc, zero
+# CHECK-ENC: encoding: [0x73,0x23,0x10,0x35]
+# CHECK-WARN: warning: 'mireg' CSR is not available on the current subtarget. Instead 'mnepc' CSR will be used.
+# uimm12
+# CHECK-INST: csrrs t2, mnepc, zero
+# CHECK-ENC: encoding: [0xf3,0x23,0x10,0x35]
+# name
+csrrs t1, mnepc, zero
+csrrs t1, mireg, zero
+# uimm12
+csrrs t2, 0x351, zero
+
+# mncause
+# name
+# CHECK-INST: csrrs t1, mncause, zero
+# CHECK-ENC: encoding: [0x73,0x23,0x20,0x35]
+# uimm12
+# CHECK-INST: csrrs t2, mncause, zero
+# CHECK-ENC: encoding: [0xf3,0x23,0x20,0x35]
+# name
+csrrs t1, mncause, zero
+# uimm12
+csrrs t2, 0x352, zero
+
+# mnstatus
+# name
+# CHECK-INST: csrrs t1, mnstatus, zero
+# CHECK-ENC: encoding: [0x73,0x23,0x30,0x35]
+# uimm12
+# CHECK-INST: csrrs t2, mnstatus, zero
+# CHECK-ENC: encoding: [0xf3,0x23,0x30,0x35]
+# name
+csrrs t1, mnstatus, zero
+# uimm12
+csrrs t2, 0x353, zero