[AVR] Insert JMP for long branches

Previously, on long branches (relative jumps of >4 kB), an assertion
failure was hit, as AVRInstrInfo::insertIndirectBranch was not
implemented. Despite its name, it is called by the branch relaxator
for *all* unconditional jumps.

Patch by Thomas Backman.

llvm-svn: 314891

lib/Target/AVR/AVRInstrInfo.cpp

@@ -537,8 +537,7 @@ bool AVRInstrInfo::isBranchOffsetInRange(unsigned BranchOp,
     llvm_unreachable("unexpected opcode!");
   case AVR::JMPk:
   case AVR::CALLk:
-    assert(BrOffset >= 0 && "offset must be absolute address");
-    return isUIntN(16, BrOffset);
+    return true;
   case AVR::RCALLk:
   case AVR::RJMPk:
     return isIntN(13, BrOffset);
@@ -556,5 +555,20 @@ bool AVRInstrInfo::isBranchOffsetInRange(unsigned BranchOp,
   }
 }
 
+unsigned AVRInstrInfo::insertIndirectBranch(MachineBasicBlock &MBB,
+                                            MachineBasicBlock &NewDestBB,
+                                            const DebugLoc &DL,
+                                            int64_t BrOffset,
+                                            RegScavenger *RS) const {
+    // This method inserts a *direct* branch (JMP), despite its name.
+    // LLVM calls this method to fixup unconditional branches; it never calls
+    // insertBranch or some hypothetical "insertDirectBranch".
+    // See lib/CodeGen/RegisterRelaxation.cpp for details.
+    // We end up here when a jump is too long for a RJMP instruction.
+    auto &MI = *BuildMI(&MBB, DL, get(AVR::JMPk)).addMBB(&NewDestBB);
+
+    return getInstSizeInBytes(MI);
+}
+
 } // end of namespace llvm
 

lib/Target/AVR/AVRInstrInfo.h

@@ -107,6 +107,12 @@ public:
 
   bool isBranchOffsetInRange(unsigned BranchOpc,
                              int64_t BrOffset) const override;
+
+  unsigned insertIndirectBranch(MachineBasicBlock &MBB,
+                                MachineBasicBlock &NewDestBB,
+                                const DebugLoc &DL,
+                                int64_t BrOffset,
+                                RegScavenger *RS) const override;
 private:
   const AVRRegisterInfo RI;
 };