[ARM][MC][Thumb] Revert relocation for some pc-relative fixups.

Summary:
This commit reverts https://reviews.llvm.org/D75039. Concensus appears to
be in favour of assembly-time resolution of these ADR and LDR relocations,
in line with GNU.

Reviewers: psmith

Subscribers: kristof.beyls, hiraditya, danielkiss, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78301

llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp

@@ -71,8 +71,7 @@ const MCFixupKindInfo &ARMAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
       // Name                      Offset (bits) Size (bits)     Flags
       {"fixup_arm_ldst_pcrel_12", 0, 32, IsPCRelConstant},
       {"fixup_t2_ldst_pcrel_12", 0, 32,
-       MCFixupKindInfo::FKF_IsPCRel |
-           MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
+       IsPCRelConstant | MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
       {"fixup_arm_pcrel_10_unscaled", 0, 32, IsPCRelConstant},
       {"fixup_arm_pcrel_10", 0, 32, IsPCRelConstant},
       {"fixup_t2_pcrel_10", 0, 32,
@@ -82,12 +81,10 @@ const MCFixupKindInfo &ARMAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
       {"fixup_t2_pcrel_9", 0, 32,
        IsPCRelConstant | MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
       {"fixup_thumb_adr_pcrel_10", 0, 8,
-       MCFixupKindInfo::FKF_IsPCRel |
-           MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
+       IsPCRelConstant | MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
       {"fixup_arm_adr_pcrel_12", 0, 32, IsPCRelConstant},
       {"fixup_t2_adr_pcrel_12", 0, 32,
-       MCFixupKindInfo::FKF_IsPCRel |
-           MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
+       IsPCRelConstant | MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
       {"fixup_arm_condbranch", 0, 24, MCFixupKindInfo::FKF_IsPCRel},
       {"fixup_arm_uncondbranch", 0, 24, MCFixupKindInfo::FKF_IsPCRel},
       {"fixup_t2_condbranch", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
@@ -119,7 +116,8 @@ const MCFixupKindInfo &ARMAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
       {"fixup_bfc_target", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
       {"fixup_bfcsel_else_target", 0, 32, 0},
       {"fixup_wls", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
-      {"fixup_le", 0, 32, MCFixupKindInfo::FKF_IsPCRel}};
+      {"fixup_le", 0, 32, MCFixupKindInfo::FKF_IsPCRel}
+  };
   const static MCFixupKindInfo InfosBE[ARM::NumTargetFixupKinds] = {
       // This table *must* be in the order that the fixup_* kinds are defined in
       // ARMFixupKinds.h.

llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp

@@ -147,13 +147,6 @@ unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
       default:
         return ELF::R_ARM_THM_CALL;
       }
-    case ARM::fixup_thumb_adr_pcrel_10:
-    case ARM::fixup_arm_thumb_cp:
-      return ELF::R_ARM_THM_PC8;
-    case ARM::fixup_t2_adr_pcrel_12:
-      return ELF::R_ARM_THM_ALU_PREL_11_0;
-    case ARM::fixup_t2_ldst_pcrel_12:
-      return ELF::R_ARM_THM_PC12;
     case ARM::fixup_bf_target:
       return ELF::R_ARM_THM_BF16;
     case ARM::fixup_bfc_target:

llvm/test/MC/ARM/pcrel-global.s

@@ -11,3 +11,11 @@ vldr d0, foo     @ arm_pcrel_10
 adr r2, foo      @ arm_adr_pcrel_12
 ldr r0, foo      @ arm_ldst_pcrel_12
 
+.thumb
+.thumb_func
+
+.globl bar
+bar:
+adr r0, bar      @ thumb_adr_pcrel_10
+adr.w r0, bar    @ t2_adr_pcrel_12
+ldr.w pc, bar    @ t2_ldst_pcrel_12

llvm/test/MC/ARM/thumb1-relax-adr.s

@@ -1,11 +1,8 @@
 @ RUN: not llvm-mc -triple thumbv6m-none-macho -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
 @ RUN: not llvm-mc -triple thumbv7m-none-macho -filetype=obj -o /dev/null %s 2>&1  | FileCheck --check-prefix=CHECK-ERROR %s
-@ RUN: llvm-mc -triple thumbv6m-none-eabi -filetype=obj %s -o - | llvm-readobj --relocs | FileCheck --check-prefix=CHECK-ELF-T1 %s
-@ RUN: llvm-mc -triple thumbv7m-none-eabi -filetype=obj %s -o - | llvm-readobj --relocs | FileCheck --check-prefix=CHECK-ELF-T2 %s
+@ RUN: not llvm-mc -triple thumbv7m-none-eabi -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
 
         .global func1
 _func1:
         adr r0, _func2
 @ CHECK-ERROR: unsupported relocation on symbol
-@ CHECK-ELF-T1: 0x0 R_ARM_THM_PC8 _func2 0x0
-@ CHECK-ELF-T2: 0x0 R_ARM_THM_ALU_PREL_11_0 _func2 0x0

llvm/test/MC/ARM/thumb1-relax-ldrlit.s

@@ -1,11 +1,8 @@
 @ RUN: not llvm-mc -triple thumbv6m-none-macho -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
 @ RUN: not llvm-mc -triple thumbv7m-none-macho -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
-@ RUN: llvm-mc -triple thumbv6m-none-eabi -filetype=obj %s -o - | llvm-readobj --relocs | FileCheck --check-prefix=CHECK-ELF-T1 %s
-@ RUN: llvm-mc -triple thumbv7m-none-eabi -filetype=obj %s -o - | llvm-readobj --relocs | FileCheck --check-prefix=CHECK-ELF-T2 %s
+@ RUN: not llvm-mc -triple thumbv7m-none-eabi -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
 
         .global func1
 _func1:
         ldr r0, _func2
 @ CHECK-ERROR: unsupported relocation on symbol
-@ CHECK-ELF-T1: 0x0 R_ARM_THM_PC8 _func2 0x0
-@ CHECK-ELF-T2: 0x0 R_ARM_THM_PC12 _func2 0x0