[RISCV] Add symbol support for the Xqcibi branch immediate instructions

This patch adds support for parsing symbols in the Xqcibi branch immediate
instructions.

Vendor relocation support will be added in a later patch.

Author: svs-quic

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

@@ -92,6 +92,7 @@ RISCVAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
       {"fixup_riscv_tlsdesc_load_lo12", 20, 12, 0},
       {"fixup_riscv_tlsdesc_add_lo12", 20, 12, 0},
       {"fixup_riscv_tlsdesc_call", 0, 0, 0},
+      {"fixup_riscv_qc_e_branch", 0, 48, MCFixupKindInfo::FKF_IsPCRel},
   };
   static_assert((std::size(Infos)) == RISCV::NumTargetFixupKinds,
                 "Not all fixup kinds added to Infos array");
@@ -165,6 +166,7 @@ bool RISCVAsmBackend::fixupNeedsRelaxationAdvanced(
     // in the range [-2048, 2046].
     return Offset > 2046 || Offset < -2048;
   case RISCV::fixup_riscv_branch:
+  case RISCV::fixup_riscv_qc_e_branch:
     // For conditional branch instructions the immediate must be
     // in the range [-4096, 4095].
     return !isInt<13>(Offset);
@@ -464,6 +466,7 @@ static uint64_t adjustFixupValue(const MCFixup &Fixup, uint64_t Value,
     Value = (Sbit << 19) | (Lo10 << 9) | (Mid1 << 8) | Hi8;
     return Value;
   }
+  case RISCV::fixup_riscv_qc_e_branch:
   case RISCV::fixup_riscv_branch: {
     if (!isInt<13>(Value))
       Ctx.reportError(Fixup.getLoc(), "fixup value out of range");

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

@@ -120,6 +120,8 @@ unsigned RISCVELFObjectWriter::getRelocType(MCContext &Ctx,
       return ELF::R_RISCV_CALL_PLT;
     case RISCV::fixup_riscv_call_plt:
       return ELF::R_RISCV_CALL_PLT;
+    case RISCV::fixup_riscv_qc_e_branch:
+      return ELF::R_RISCV_QC_E_BRANCH;
     }
   }
 

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

@@ -77,6 +77,9 @@ enum Fixups {
   fixup_riscv_tlsdesc_load_lo12,
   fixup_riscv_tlsdesc_add_lo12,
   fixup_riscv_tlsdesc_call,
+  // 12-bit fixup for symbol references in the 48-bit Xqcibi branch immediate
+  // instructions
+  fixup_riscv_qc_e_branch,
 
   // Used as a sentinel, must be the last
   fixup_riscv_invalid,

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

@@ -569,6 +569,8 @@ uint64_t RISCVMCCodeEmitter::getImmOpValue(const MCInst &MI, unsigned OpNo,
       FixupKind = RISCV::fixup_riscv_rvc_branch;
     } else if (MIFrm == RISCVII::InstFormatI) {
       FixupKind = RISCV::fixup_riscv_12_i;
+    } else if (MIFrm == RISCVII::InstFormatQC_EB) {
+      FixupKind = RISCV::fixup_riscv_qc_e_branch;
     }
   }
 

llvm/lib/Target/RISCV/RISCVInstrInfoXqci.td

@@ -550,7 +550,7 @@ class QCIBranchInst_rii<bits<3> funct3, DAGOperand InTyImm5, string opcodestr>
 class QCIBranchInst48_rii<bits<5> funct5, DAGOperand InTyImm16, string opcodestr>
     : RVInst48<(outs),
                (ins GPRNoX0:$rs1, InTyImm16:$imm16, bare_simm13_lsb0:$imm12),
-               opcodestr, "$rs1, $imm16, $imm12", [], InstFormatOther> {
+               opcodestr, "$rs1, $imm16, $imm12", [], InstFormatQC_EB> {
   bits<5> rs1;
   bits<16> imm16;
   bits<12> imm12;

llvm/test/MC/RISCV/xqcibi-relocations.s

@@ -0,0 +1,44 @@
+# RUN: llvm-mc -triple riscv32 -mattr=+experimental-xqcibi %s -show-encoding \
+# RUN:     | FileCheck -check-prefix=INSTR -check-prefix=FIXUP %s
+# RUN: llvm-mc -filetype=obj -triple riscv32 -mattr=+experimental-xqcibi %s -o %t.o
+# RUN: llvm-readobj -r %t.o | FileCheck -check-prefix=RELOC %s
+
+# Check prefixes:
+# RELOC - Check the relocation in the object.
+# FIXUP - Check the fixup on the instruction.
+# INSTR - Check the instruction is handled properly by the ASMPrinter.
+
+.text
+
+# Check that branch to an undefined symbol is handled
+# FIXME: This should be relaxed to an inverse  branch and jump
+qc.bnei x6, 10, foo
+# RELOC: R_RISCV_BRANCH foo 0x0
+# INSTR: qc.bnei t1, 10, foo
+# FIXUP: fixup A - offset: 0, value: foo, kind: fixup_riscv_branch
+
+# FIXME: This should be relaxed to an inverse  branch and jump
+qc.e.bgeui x8, 12, foo
+# RELOC: R_RISCV_CUSTOM193 foo 0x0
+# INSTR: qc.e.bgeui s0, 12, foo
+# FIXUP: fixup A - offset: 0, value: foo, kind: fixup_riscv_qc_e_branch
+
+# Check that a label in a different section is handled similar to an undefined symbol
+# FIXME: This should be relaxed to an inverse  branch and jump
+qc.e.bltui x4, 9, .bar
+# RELOC: R_RISCV_CUSTOM193 .bar 0x0
+# INSTR: qc.e.bltui tp, 9, .bar
+# FIXUP: fixup A - offset: 0, value: .bar, kind: fixup_riscv_qc_e_branch
+
+# Check that branches to a defined symbol are handled correctly
+qc.e.beqi x7, 8, .L1
+# INSTR: qc.e.beqi t2, 8, .L1
+# FIXUP: fixup A - offset: 0, value: .L1, kind: fixup_riscv_qc_e_branch
+
+.L1:
+  ret
+
+.section .t2
+
+.bar:
+  ret