[AVR] Fix inaccurate offsets in PC relative branch instructions

[benshi001]

Summary

In avr-gcc, the destination of rjmp label + offset is address
label + offset, while destination of rjmp . + offset is
address_of_rjmp + offset + 2.

Clang is in accordance with avr-gcc for rjmp label + offset, but
emits incorrect destination of rjmp . + offset to address_of_rjmp + offset,
in which the expected offset 2 is missing.

This patch fixes the above issue.

Fixes https://github.com/llvm/llvm-project/issues/60019

[jacquesguan]

LGTM.

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

bool AVRAsmBackend::shouldForceRelocation(const MCAssembler &Asm,
                                           const MCFixup &Fixup,
                                           const MCValue &Target) {
   switch ((unsigned)Fixup.getKind()) {
   default:
     return Fixup.getKind() >= FirstLiteralRelocationKind;
   // Fixups which should always be recorded as relocations.
   case AVR::fixup_7_pcrel:
   case AVR::fixup_13_pcrel:
+    // Do not force relocation for PC relative branch like 'rjmp .',
+    // 'rcall . - off' and 'breq . + off'.
+    if (const auto *SymA = Target.getSymA())
+      if (SymA->getSymbol().getName().size() == 0)
+        return false;
+    [[fallthrough]];
   case AVR::fixup_call:
     return true;
   }
 }
 
 MCAsmBackend *createAVRAsmBackend(const Target &T, const MCSubtargetInfo &STI,
                                   const MCRegisterInfo &MRI,
                                   const llvm::MCTargetOptions &TO) {
   return new AVRAsmBackend(STI.getTargetTriple().getOS());
 }
 
 } // end of namespace llvm

llvm/test/MC/AVR/inst-brbc.s

foo:
   .short 0xf74c
   .short 0xf4c7
 
 ; CHECK: brvc .Ltmp0+8              ; encoding: [0bAAAAA011,0b111101AA]
 ; CHECK:                            ; fixup A - offset: 0, value: .Ltmp0+8, kind: fixup_7_pcrel
 ; CHECK: brcc .Ltmp1-16             ; encoding: [0bAAAAA000,0b111101AA]
 ; CHECK:                            ; fixup A - offset: 0, value: .Ltmp1-16, kind: fixup_7_pcrel
 
-; INST: brvc .+0
-; INST: brsh .+0
-; INST: brne .-42
-; INST: brpl .-44
-; INST: brge .-46
-; INST: brid .+48
+; INST: 23 f4   brvc .+8
+; INST: c0 f7   brsh .-16
+; INST: 59 f7   brne .-42
+; INST: 52 f7   brpl .-44
+; INST: 4c f7   brge .-46
+; INST: c7 f4   brid .+48

llvm/test/MC/AVR/inst-brbs.s

foo:
   .short 0xf34c
   .short 0xf077
 
 ; CHECK: brvs .Ltmp0+8              ; encoding: [0bAAAAA011,0b111100AA]
 ; CHECK:                            ; fixup A - offset: 0, value: .Ltmp0+8, kind: fixup_7_pcrel
 ; CHECK: brcs .Ltmp1-12             ; encoding: [0bAAAAA000,0b111100AA]
 ; CHECK:                            ; fixup A - offset: 0, value: .Ltmp1-12, kind: fixup_7_pcrel
 
-; INST: brvs .+0
-; INST: brlo .+0
-; INST: breq .-42
-; INST  brmi .-44
-; INST  brlt .-46
-; InST: brie .+28
+; INST: 23 f0   brvs .+8
+; INST: d0 f3   brlo .-12
+; INST: 59 f3   breq .-42
+; INST: 52 f3   brmi .-44
+; INST: 4c f3   brlt .-46
+; INST: 77 f0   brie .+28

llvm/test/MC/AVR/inst-family-cond-branch.s

 ; CHECK: breq    .Ltmp1-12               ; encoding: [0bAAAAA001,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp1-12, kind: fixup_7_pcrel
 ; CHECK: brbs    1, .Ltmp2-18            ; encoding: [0bAAAAA001,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp2-18, kind: fixup_7_pcrel
 ; CHECK: brbs    1, baz                  ; encoding: [0bAAAAA001,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: baz, kind: fixup_7_pcrel
 
 ; INST-LABEL: <foo>:
-; INST: breq .+0
-; INST: breq .+0
-; INST: breq .+0
+; INST: breq .-18
+; INST: breq .-12
+; INST: breq .-18
 ; INST: breq .+0
 
   ; BRNE
   brne .+10
   brne .+2
   brbc 1, .+10
   brbc 1, bar
 
 ; CHECK: brne    .Ltmp3+10               ; encoding: [0bAAAAA001,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp3+10, kind: fixup_7_pcrel
 ; CHECK: brne    .Ltmp4+2                ; encoding: [0bAAAAA001,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp4+2, kind: fixup_7_pcrel
 ; CHECK: brbc    1, .Ltmp5+10            ; encoding: [0bAAAAA001,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp5+10, kind: fixup_7_pcrel
 ; CHECK: brbc    1, bar                  ; encoding: [0bAAAAA001,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: bar, kind: fixup_7_pcrel
 
-; INST: brne .+0
-; INST: brne .+0
-; INST: brne .+0
+; INST: brne .+10
+; INST: brne .+2
+; INST: brne .+10
 ; INST: brne .+0
 
 bar:
   ; BRCS
   brcs .+8
   brcs .+4
   brbs 0, .+8
   brbs 0, end
 
 ; CHECK: brcs    .Ltmp6+8                ; encoding: [0bAAAAA000,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp6+8, kind: fixup_7_pcrel
 ; CHECK: brcs    .Ltmp7+4                ; encoding: [0bAAAAA000,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp7+4, kind: fixup_7_pcrel
 ; CHECK: brcs    .Ltmp8+8                ; encoding: [0bAAAAA000,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp8+8, kind: fixup_7_pcrel
 ; CHECK: brcs    end                     ; encoding: [0bAAAAA000,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: end, kind: fixup_7_pcrel
 
 ; INST-LABEL: <bar>:
-; INST: brlo .+0
-; INST: brlo .+0
-; INST: brlo .+0
+; INST: brlo .+8
+; INST: brlo .+4
+; INST: brlo .+8
 ; INST: brlo .+0
 
   ; BRCC
   brcc .+66
   brcc .-22
   brbc 0, .+66
   brbc 0, baz
 
 ; CHECK: brcc    .Ltmp9+66               ; encoding: [0bAAAAA000,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp9+66, kind: fixup_7_pcrel
 ; CHECK: brcc    .Ltmp10-22              ; encoding: [0bAAAAA000,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp10-22, kind: fixup_7_pcrel
 ; CHECK: brcc    .Ltmp11+66              ; encoding: [0bAAAAA000,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp11+66, kind: fixup_7_pcrel
 ; CHECK: brcc    baz                     ; encoding: [0bAAAAA000,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: baz, kind: fixup_7_pcrel
 
-; INST: brsh .+0
-; INST: brsh .+0
-; INST: brsh .+0
+; INST: brsh .+66
+; INST: brsh .-22
+; INST: brsh .+66
 ; INST: brsh .+0
 
 ; BRSH
   brsh .+32
   brsh .+70
   brsh car
 
 ; CHECK: brsh    .Ltmp12+32              ; encoding: [0bAAAAA000,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp12+32, kind: fixup_7_pcrel
 ; CHECK: brsh    .Ltmp13+70              ; encoding: [0bAAAAA000,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp13+70, kind: fixup_7_pcrel
 ; CHECK: brsh    car                     ; encoding: [0bAAAAA000,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: car, kind: fixup_7_pcrel
 
-; INST: brsh .+0
-; INST: brsh .+0
+; INST: brsh .+32
+; INST: brsh .+70
 ; INST: brsh .+0
 
 baz:
 
   ; BRLO
   brlo .+12
   brlo .+28
   brlo car
 
 ; CHECK: brlo    .Ltmp14+12              ; encoding: [0bAAAAA000,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp14+12, kind: fixup_7_pcrel
 ; CHECK: brlo    .Ltmp15+28              ; encoding: [0bAAAAA000,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp15+28, kind: fixup_7_pcrel
 ; CHECK: brlo    car                     ; encoding: [0bAAAAA000,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: car, kind: fixup_7_pcrel
 
 ; INST-LABEL: <baz>:
-; INST: brlo .+0
-; INST: brlo .+0
+; INST: brlo .+12
+; INST: brlo .+28
 ; INST: brlo .+0
 
   ; BRMI
   brmi .+66
   brmi .+58
   brmi car
 
 ; CHECK: brmi    .Ltmp16+66              ; encoding: [0bAAAAA010,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp16+66, kind: fixup_7_pcrel
 ; CHECK: brmi    .Ltmp17+58              ; encoding: [0bAAAAA010,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp17+58, kind: fixup_7_pcrel
 ; CHECK: brmi    car                     ; encoding: [0bAAAAA010,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: car, kind: fixup_7_pcrel
 
-; INST: brmi .+0
-; INST: brmi .+0
+; INST: brmi .+66
+; INST: brmi .+58
 ; INST: brmi .+0
 
   ; BRPL
   brpl .-12
   brpl .+18
   brpl car
 
 ; CHECK: brpl    .Ltmp18-12              ; encoding: [0bAAAAA010,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp18-12, kind: fixup_7_pcrel
 ; CHECK: brpl    .Ltmp19+18              ; encoding: [0bAAAAA010,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp19+18, kind: fixup_7_pcrel
 ; CHECK: brpl    car                     ; encoding: [0bAAAAA010,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: car, kind: fixup_7_pcrel
 
-; INST: brpl .+0
-; INST: brpl .+0
+; INST: brpl .-12
+; INST: brpl .+18
 ; INST: brpl .+0
 
 ; BRGE
   brge .+50
   brge .+42
   brge car
 
 ; CHECK: brge    .Ltmp20+50              ; encoding: [0bAAAAA100,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp20+50, kind: fixup_7_pcrel
 ; CHECK: brge    .Ltmp21+42              ; encoding: [0bAAAAA100,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp21+42, kind: fixup_7_pcrel
 ; CHECK: brge    car                     ; encoding: [0bAAAAA100,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: car, kind: fixup_7_pcrel
 
-; INST: brge .+0
-; INST: brge .+0
+; INST: brge .+50
+; INST: brge .+42
 ; INST: brge .+0
 
 car:
   ; BRLT
   brlt .+16
   brlt .+2
   brlt end
 
 ; CHECK: brlt    .Ltmp22+16              ; encoding: [0bAAAAA100,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp22+16, kind: fixup_7_pcrel
 ; CHECK: brlt    .Ltmp23+2               ; encoding: [0bAAAAA100,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp23+2, kind: fixup_7_pcrel
 ; CHECK: brlt    end                     ; encoding: [0bAAAAA100,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: end, kind: fixup_7_pcrel
 
 ; INST-LABEL: <car>:
-; INST: brlt  .+0
-; INST: brlt  .+0
+; INST: brlt  .+16
+; INST: brlt  .+2
 ; INST: brlt  .+0
 
   ; BRHS
   brhs .-66
   brhs .+14
   brhs just_another_label
 
 ; CHECK: brhs    .Ltmp24-66              ; encoding: [0bAAAAA101,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp24-66, kind: fixup_7_pcrel
 ; CHECK: brhs    .Ltmp25+14              ; encoding: [0bAAAAA101,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp25+14, kind: fixup_7_pcrel
 ; CHECK: brhs    just_another_label      ; encoding: [0bAAAAA101,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: just_another_label, kind: fixup_7_pcrel
 
-; INST: brhs  .+0
-; INST: brhs  .+0
+; INST: brhs  .-66
+; INST: brhs  .+14
 ; INST: brhs  .+0
 
   ; BRHC
   brhc .+12
   brhc .+14
   brhc just_another_label
 
 ; CHECK: brhc    .Ltmp26+12              ; encoding: [0bAAAAA101,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp26+12, kind: fixup_7_pcrel
 ; CHECK: brhc    .Ltmp27+14              ; encoding: [0bAAAAA101,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp27+14, kind: fixup_7_pcrel
 ; CHECK: brhc    just_another_label      ; encoding: [0bAAAAA101,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: just_another_label, kind: fixup_7_pcrel
 
-; INST: brhc  .+0
-; INST: brhc  .+0
+; INST: brhc  .+12
+; INST: brhc  .+14
 ; INST: brhc  .+0
 
   ; BRTS
   brts .+18
   brts .+22
   brts just_another_label
 
 ; CHECK: brts    .Ltmp28+18              ; encoding: [0bAAAAA110,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp28+18, kind: fixup_7_pcrel
 ; CHECK: brts    .Ltmp29+22              ; encoding: [0bAAAAA110,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp29+22, kind: fixup_7_pcrel
 ; CHECK: brts    just_another_label      ; encoding: [0bAAAAA110,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: just_another_label, kind: fixup_7_pcrel
 
-; INST: brts  .+0
-; INST: brts  .+0
+; INST: brts  .+18
+; INST: brts  .+22
 ; INST: brts  .+0
 
 just_another_label:
   ; BRTC
   brtc .+52
   brtc .+50
   brtc end
 
 ; CHECK: brtc    .Ltmp30+52              ; encoding: [0bAAAAA110,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp30+52, kind: fixup_7_pcrel
 ; CHECK: brtc    .Ltmp31+50              ; encoding: [0bAAAAA110,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp31+50, kind: fixup_7_pcrel
 ; CHECK: brtc    end                     ; encoding: [0bAAAAA110,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: end, kind: fixup_7_pcrel
 
 ; INST-LABEL: <just_another_label>:
-; INST: brtc  .+0
-; INST: brtc  .+0
+; INST: brtc  .+52
+; INST: brtc  .+50
 ; INST: brtc  .+0
 
   ; BRVS
   brvs .+18
   brvs .+32
   brvs end
 
 ; CHECK: brvs    .Ltmp32+18              ; encoding: [0bAAAAA011,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp32+18, kind: fixup_7_pcrel
 ; CHECK: brvs    .Ltmp33+32              ; encoding: [0bAAAAA011,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp33+32, kind: fixup_7_pcrel
 ; CHECK: brvs    end                     ; encoding: [0bAAAAA011,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: end, kind: fixup_7_pcrel
 
-; INST: brvs  .+0
-; INST: brvs  .+0
+; INST: brvs  .+18
+; INST: brvs  .+32
 ; INST: brvs  .+0
 
   ; BRVC
   brvc .-28
   brvc .-62
   brvc end
 
 ; CHECK: brvc    .Ltmp34-28              ; encoding: [0bAAAAA011,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp34-28, kind: fixup_7_pcrel
 ; CHECK: brvc    .Ltmp35-62              ; encoding: [0bAAAAA011,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp35-62, kind: fixup_7_pcrel
 ; CHECK: brvc    end                     ; encoding: [0bAAAAA011,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: end, kind: fixup_7_pcrel
 
-; INST: brvc  .+0
-; INST: brvc  .+0
+; INST: brvc  .-28
+; INST: brvc  .-62
 ; INST: brvc  .+0
 
   ; BRIE
   brie .+20
   brie .+40
   brie end
 
 ; CHECK: brie    .Ltmp36+20              ; encoding: [0bAAAAA111,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp36+20, kind: fixup_7_pcrel
 ; CHECK: brie    .Ltmp37+40              ; encoding: [0bAAAAA111,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp37+40, kind: fixup_7_pcrel
 ; CHECK: brie    end                     ; encoding: [0bAAAAA111,0b111100AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: end, kind: fixup_7_pcrel
 
-; INST: brie  .+0
-; INST: brie  .+0
+; INST: brie  .+20
+; INST: brie  .+40
 ; INST: brie  .+0
 
   ; BRID
   brid .+42
   brid .+62
   brid end
 
 ; CHECK: brid    .Ltmp38+42              ; encoding: [0bAAAAA111,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp38+42, kind: fixup_7_pcrel
 ; CHECK: brid    .Ltmp39+62              ; encoding: [0bAAAAA111,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp39+62, kind: fixup_7_pcrel
 ; CHECK: brid    end                     ; encoding: [0bAAAAA111,0b111101AA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: end, kind: fixup_7_pcrel
 
-; INST: brid  .+0
-; INST: brid  .+0
+; INST: brid  .+42
+; INST: brid  .+62
 ; INST: brid  .+0
 
 end:

llvm/test/MC/AVR/inst-rcall.s

 ; CHECK:                             ;   fixup A - offset: 0, value: .Ltmp0+0, kind: fixup_13_pcrel
 ; CHECK: rcall  .Ltmp1-8             ; encoding: [A,0b1101AAAA]
 ; CHECK:                             ;   fixup A - offset: 0, value: .Ltmp1-8, kind: fixup_13_pcrel
 ; CHECK: rcall  .Ltmp2+12            ; encoding: [A,0b1101AAAA]
 ; CHECK:                             ;   fixup A - offset: 0, value: .Ltmp2+12, kind: fixup_13_pcrel
 ; CHECK: rcall  .Ltmp3+46            ; encoding: [A,0b1101AAAA]
 ; CHECK:                             ;   fixup A - offset: 0, value: .Ltmp3+46, kind: fixup_13_pcrel
 
-; INST: rcall   .+0
-; INST: rcall   .+0
-; INST: rcall   .+0
-; INST: rcall   .+0
-; INST: rcall   .-44
+; INST: 00 d0    rcall .+0
+; INST: fc df    rcall .-8
+; INST: 06 d0    rcall .+12
+; INST: 17 d0    rcall .+46
+; INST: ea df    rcall .-44

llvm/test/MC/AVR/inst-rjmp.s

 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp3+0, kind: fixup_13_pcrel
 ; CHECK: rjmp    .Ltmp4-4                ; encoding: [A,0b1100AAAA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp4-4, kind: fixup_13_pcrel
 ; CHECK: rjmp    .Ltmp5-6                ; encoding: [A,0b1100AAAA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: .Ltmp5-6, kind: fixup_13_pcrel
 ; CHECK: rjmp    x                       ; encoding: [A,0b1100AAAA]
 ; CHECK:                                 ;   fixup A - offset: 0, value: x, kind: fixup_13_pcrel
 
-; INST: rjmp  .+0
-; INST: rjmp  .+0
-; INST: rjmp  .+0
-; INST: rjmp  .+0
-; INST: rjmp  .+0
-; INST: rjmp  .+0
-; INST: rjmp  .+0
-; INST: rjmp  .+0
-; INST: rjmp  .+0
-; INST: rjmp  .+30
+; INST: 01 c0      rjmp  .+2
+; INST: ff cf      rjmp  .-2
+; INST: 00 c0      rjmp  .+0
+; INST: 04 c0      rjmp  .+8
+; INST: 00 c0      rjmp  .+0
+; INST: 00 c0      rjmp  .+0
+; INST: fe cf      rjmp  .-4
+; INST: fd cf      rjmp  .-6
+; INST: 00 c0      rjmp  .+0
+; INST: 0f c0      rjmp  .+30