[RISCV] Indirect branch generation in position independent code

This fixes the "Unable to insert indirect branch" fatal error sometimes
seen when generating position-independent code.

Patch by msizanoen1

Reviewed By: jrtc27

Differential Revision: https://reviews.llvm.org/D84833

(cherry picked from commit 5f9ecc5)

Author: lenary

llvm/lib/Target/RISCV/RISCVInstrInfo.cpp

@@ -279,7 +279,7 @@ bool RISCVInstrInfo::analyzeBranch(MachineBasicBlock &MBB,
 
   // Handle a single unconditional branch.
   if (NumTerminators == 1 && I->getDesc().isUnconditionalBranch()) {
-    TBB = I->getOperand(0).getMBB();
+    TBB = getBranchDestBlock(*I);
     return false;
   }
 
@@ -293,7 +293,7 @@ bool RISCVInstrInfo::analyzeBranch(MachineBasicBlock &MBB,
   if (NumTerminators == 2 && std::prev(I)->getDesc().isConditionalBranch() &&
       I->getDesc().isUnconditionalBranch()) {
     parseCondBranch(*std::prev(I), TBB, Cond);
-    FBB = I->getOperand(0).getMBB();
+    FBB = getBranchDestBlock(*I);
     return false;
   }
 
@@ -384,10 +384,6 @@ unsigned RISCVInstrInfo::insertIndirectBranch(MachineBasicBlock &MBB,
 
   MachineFunction *MF = MBB.getParent();
   MachineRegisterInfo &MRI = MF->getRegInfo();
-  const auto &TM = static_cast<const RISCVTargetMachine &>(MF->getTarget());
-
-  if (TM.isPositionIndependent())
-    report_fatal_error("Unable to insert indirect branch");
 
   if (!isInt<32>(BrOffset))
     report_fatal_error(
@@ -399,15 +395,13 @@ unsigned RISCVInstrInfo::insertIndirectBranch(MachineBasicBlock &MBB,
   Register ScratchReg = MRI.createVirtualRegister(&RISCV::GPRRegClass);
   auto II = MBB.end();
 
-  MachineInstr &LuiMI = *BuildMI(MBB, II, DL, get(RISCV::LUI), ScratchReg)
-                             .addMBB(&DestBB, RISCVII::MO_HI);
-  BuildMI(MBB, II, DL, get(RISCV::PseudoBRIND))
-      .addReg(ScratchReg, RegState::Kill)
-      .addMBB(&DestBB, RISCVII::MO_LO);
+  MachineInstr &MI = *BuildMI(MBB, II, DL, get(RISCV::PseudoJump))
+                          .addReg(ScratchReg, RegState::Define | RegState::Dead)
+                          .addMBB(&DestBB, RISCVII::MO_CALL);
 
   RS->enterBasicBlockEnd(MBB);
   unsigned Scav = RS->scavengeRegisterBackwards(RISCV::GPRRegClass,
-                                                LuiMI.getIterator(), false, 0);
+                                                MI.getIterator(), false, 0);
   MRI.replaceRegWith(ScratchReg, Scav);
   MRI.clearVirtRegs();
   RS->setRegUsed(Scav);
@@ -431,6 +425,7 @@ RISCVInstrInfo::getBranchDestBlock(const MachineInstr &MI) const {
 
 bool RISCVInstrInfo::isBranchOffsetInRange(unsigned BranchOp,
                                            int64_t BrOffset) const {
+  unsigned XLen = STI.getXLen();
   // Ideally we could determine the supported branch offset from the
   // RISCVII::FormMask, but this can't be used for Pseudo instructions like
   // PseudoBR.
@@ -447,6 +442,8 @@ bool RISCVInstrInfo::isBranchOffsetInRange(unsigned BranchOp,
   case RISCV::JAL:
   case RISCV::PseudoBR:
     return isIntN(21, BrOffset);
+  case RISCV::PseudoJump:
+    return isIntN(32, SignExtend64(BrOffset + 0x800, XLen));
   }
 }
 

llvm/lib/Target/RISCV/RISCVInstrInfo.td

@@ -1012,8 +1012,8 @@ def : Pat<(riscv_tail (iPTR tglobaladdr:$dst)),
 def : Pat<(riscv_tail (iPTR texternalsym:$dst)),
           (PseudoTAIL texternalsym:$dst)>;
 
-let isCall = 0, isBarrier = 0, isCodeGenOnly = 0, hasSideEffects = 0,
-    mayStore = 0, mayLoad = 0 in
+let isCall = 0, isBarrier = 1, isBranch = 1, isTerminator = 1,
+    isCodeGenOnly = 0, hasSideEffects = 0, mayStore = 0, mayLoad = 0 in
 def PseudoJump : Pseudo<(outs GPR:$rd), (ins pseudo_jump_symbol:$target), []> {
   let AsmString = "jump\t$target, $rd";
 }

llvm/test/CodeGen/RISCV/branch-relaxation.ll

@@ -1,7 +1,11 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
 ; RUN: llc -mtriple=riscv32 -verify-machineinstrs -filetype=obj < %s \
 ; RUN:   -o /dev/null 2>&1
+; RUN: llc -mtriple=riscv32 -relocation-model=pic -verify-machineinstrs \
+; RUN:   -filetype=obj < %s -o /dev/null 2>&1
 ; RUN: llc -mtriple=riscv32 -verify-machineinstrs < %s | FileCheck %s
+; RUN: llc -mtriple=riscv32 -relocation-model=pic -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s
 
 define void @relax_bcc(i1 %a) nounwind {
 ; CHECK-LABEL: relax_bcc:
@@ -25,15 +29,13 @@ tail:
   ret void
 }
 
-; TODO: Extend simm12's MCOperandPredicate so the jalr zero is printed as a jr.
 define i32 @relax_jal(i1 %a) nounwind {
 ; CHECK-LABEL: relax_jal:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    andi a0, a0, 1
 ; CHECK-NEXT:    bnez a0, .LBB1_1
 ; CHECK-NEXT:  # %bb.3:
-; CHECK-NEXT:    lui a0, %hi(.LBB1_2)
-; CHECK-NEXT:    jalr zero, %lo(.LBB1_2)(a0)
+; CHECK-NEXT:    jump .LBB1_2, a0
 ; CHECK-NEXT:  .LBB1_1: # %iftrue
 ; CHECK-NEXT:    #APP
 ; CHECK-NEXT:    #NO_APP