[3/4][RISCV][MC] Teach MCInstrAnalysis::evaluateBranch to determine the target of an auipc+jalr

[asb]

Summary

Now that MCInstrAnalysis takes a previousInst argument, it can be used
to determine the target of a pair of auipc+jalr instructions.

[asb]

Rebase.

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

if (Inst.getOpcode() == RISCV::C_JAL || Inst.getOpcode() == RISCV::C_J) {
       return true;
     }
 
     if (Inst.getOpcode() == RISCV::JAL) {
       Target = Addr + Inst.getOperand(1).getImm();
       return true;
     }
 
+    if (Inst.getOpcode() == RISCV::JALR && PreviousInst.hasValue() &&
+        PreviousInst->getOpcode() == RISCV::AUIPC &&
+        PreviousInst->getOperand(0).getReg() == Inst.getOperand(1).getReg()) {
+      Target = Addr + Inst.getOperand(2).getImm() +
+               PreviousInst->getOperand(1).getImm() - 4;
+      return true;
+    }
+
     return false;
   }
 };
 
 } // end anonymous namespace
 
 static MCInstrAnalysis *createRISCVInstrAnalysis(const MCInstrInfo *Info) {
   return new RISCVMCInstrAnalysis(Info);

llvm/test/tools/llvm-objdump/ELF/RISCV/branches.s

 jal t0, bar
 # CHECK: 44: c.jal 0x60 <bar>
 c.jal bar
 
 # CHECK: 46: c.j 0x60 <bar>
 c.j bar
 
 # CHECK: 48: auipc ra, 0
-# CHECK: 4c: jalr ra, 16(ra)
+# CHECK: 4c: jalr ra, 16(ra) <foo+0x58>
 call .Llocal
 
 # CHECK: 50: auipc ra, 0
-# CHECK: 54: jalr ra, 16(ra)
+# CHECK: 54: jalr ra, 16(ra) <bar>
 call bar
 
 .Llocal:
 # CHECK: 58: c.nop
 # CHECK: 5a: c.nop
 # CHECK: 5c: c.nop
 # CHECK: 5e: c.nop
 nop
 nop
 nop
 nop
 
 # CHECK: 00000060 <bar>:
 bar:
 # CHECK: 60: c.nop
 nop