[LLVM][AVR] Support for R_AVR_6 fixup

Summary: Handle the emission of `R_AVR_6` ELF relocation type.

Reviewers: dylanmckay

Reviewed By: dylanmckay

Subscribers: hiraditya, Jim, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78721

Patch by @LemonBoy https://reviews.llvm.org/p/LemonBoy/

Author: dylanmckay

llvm/lib/Target/AVR/MCTargetDesc/AVRAsmBackend.cpp

@@ -139,6 +139,18 @@ void fixup_13_pcrel(unsigned Size, const MCFixup &Fixup, uint64_t &Value,
   Value &= 0xfff;
 }
 
+/// 6-bit fixup for the immediate operand of the STD/LDD family of
+/// instructions.
+///
+/// Resolves to:
+/// 10q0 qq10 0000 1qqq
+static void fixup_6(const MCFixup &Fixup, uint64_t &Value,
+                    MCContext *Ctx = nullptr) {
+  unsigned_width(6, Value, std::string("immediate"), Fixup, Ctx);
+
+  Value = ((Value & 0x20) << 8) | ((Value & 0x18) << 7) | (Value & 0x07);
+}
+
 /// 6-bit fixup for the immediate operand of the ADIW family of
 /// instructions.
 ///
@@ -336,6 +348,9 @@ void AVRAsmBackend::adjustFixupValue(const MCFixup &Fixup,
     Value &= 0xffff;
     break;
 
+  case AVR::fixup_6:
+    adjust::fixup_6(Fixup, Value, Ctx);
+    break;
   case AVR::fixup_6_adiw:
     adjust::fixup_6_adiw(Fixup, Value, Ctx);
     break;

llvm/test/MC/AVR/relocations.s

@@ -9,6 +9,9 @@ bar:
 ; CHECK: R_AVR_LDI SYMBOL+0x3
 ldi r21, SYMBOL+3
 
+; CHECK: R_AVR_6 SYMBOL+0x4
+ldd r8, Y+SYMBOL+4
+
 ; CHECK-NEXT: R_AVR_6_ADIW FOO
 adiw r24, FOO