[ELF] Add TargetInfo::adjustGotPcExpr for `R_GOT_PC` relaxations. NFC

[MaskRay]

Summary

With this change, TargetInfo::adjustRelaxExpr is only related to TLS
relaxations and a subsequent clean-up can delete the data parameter.

lld/ELF/Arch/PPC64.cpp

public:
   void writeGotHeader(uint8_t *buf) const override;
   bool needsThunk(RelExpr expr, RelType type, const InputFile *file,
                   uint64_t branchAddr, const Symbol &s,
                   int64_t a) const override;
   uint32_t getThunkSectionSpacing() const override;
   bool inBranchRange(RelType type, uint64_t src, uint64_t dst) const override;
   RelExpr adjustRelaxExpr(RelType type, const uint8_t *data,
                           RelExpr expr) const override;
+  RelExpr adjustGotPcExpr(RelType type, int64_t addend,
+                          const uint8_t *loc) const override;
   void relaxGot(uint8_t *loc, const Relocation &rel,
                 uint64_t val) const override;
   void relaxTlsGdToIe(uint8_t *loc, const Relocation &rel,
                       uint64_t val) const override;
   void relaxTlsGdToLe(uint8_t *loc, const Relocation &rel,
                       uint64_t val) const override;
   void relaxTlsLdToLe(uint8_t *loc, const Relocation &rel,
                       uint64_t val) const override;
if (type == R_PPC64_REL14)
     return isInt<16>(offset);
   if (type == R_PPC64_REL24 || type == R_PPC64_REL24_NOTOC)
     return isInt<26>(offset);
   llvm_unreachable("unsupported relocation type used in branch");
 }
 
 RelExpr PPC64::adjustRelaxExpr(RelType type, const uint8_t *data,
                                RelExpr expr) const {
+  if (type != R_PPC64_GOT_TLSGD_PCREL34 && expr == R_RELAX_TLS_GD_TO_IE)
+    return R_RELAX_TLS_GD_TO_IE_GOT_OFF;
+  if (expr == R_RELAX_TLS_LD_TO_LE)
+    return R_RELAX_TLS_LD_TO_LE_ABS;
+  return expr;
+}
+
+RelExpr PPC64::adjustGotPcExpr(RelType type, int64_t addend,
+                               const uint8_t *loc) const {
   if ((type == R_PPC64_GOT_PCREL34 || type == R_PPC64_PCREL_OPT) &&
       config->pcRelOptimize) {
     // It only makes sense to optimize pld since paddi means that the address
     // of the object in the GOT is required rather than the object itself.
-    assert(data && "Expecting an instruction encoding here");
-    if ((readPrefixedInstruction(data) & 0xfc000000) == 0xe4000000)
+    if ((readPrefixedInstruction(loc) & 0xfc000000) == 0xe4000000)
       return R_PPC64_RELAX_GOT_PC;
   }
-
-  if (type != R_PPC64_GOT_TLSGD_PCREL34 && expr == R_RELAX_TLS_GD_TO_IE)
-    return R_RELAX_TLS_GD_TO_IE_GOT_OFF;
-  if (expr == R_RELAX_TLS_LD_TO_LE)
-    return R_RELAX_TLS_LD_TO_LE_ABS;
-  return expr;
+  return R_GOT_PC;
 }
 
 // Reference: 3.7.4.1 of the 64-bit ELF V2 abi supplement.
 // The general dynamic code sequence for a global `x` uses 4 instructions.
 // Instruction                    Relocation                Symbol
 // addis r3, r2, x@got@tlsgd@ha   R_PPC64_GOT_TLSGD16_HA      x
 // addi  r3, r3, x@got@tlsgd@l    R_PPC64_GOT_TLSGD16_LO      x
 // bl __tls_get_addr(x@tlsgd)     R_PPC64_TLSGD               x

lld/ELF/Arch/X86_64.cpp

public:
   void writePltHeader(uint8_t *buf) const override;
   void writePlt(uint8_t *buf, const Symbol &sym,
                 uint64_t pltEntryAddr) const override;
   void relocate(uint8_t *loc, const Relocation &rel,
                 uint64_t val) const override;
   void applyJumpInstrMod(uint8_t *loc, JumpModType type,
                          unsigned size) const override;
 
-  RelExpr adjustRelaxExpr(RelType type, const uint8_t *data,
-                          RelExpr expr) const override;
+  RelExpr adjustGotPcExpr(RelType type, int64_t addend,
+                          const uint8_t *loc) const override;
   void relaxGot(uint8_t *loc, const Relocation &rel,
                 uint64_t val) const override;
   void relaxTlsGdToIe(uint8_t *loc, const Relocation &rel,
                       uint64_t val) const override;
   void relaxTlsGdToLe(uint8_t *loc, const Relocation &rel,
                       uint64_t val) const override;
   void relaxTlsIeToLe(uint8_t *loc, const Relocation &rel,
                       uint64_t val) const override;
void X86_64::relocate(uint8_t *loc, const Relocation &rel, uint64_t val) const {
   case R_X86_64_GOTPC64:
     write64le(loc, val);
     break;
   default:
     llvm_unreachable("unknown relocation");
   }
 }
 
-RelExpr X86_64::adjustRelaxExpr(RelType type, const uint8_t *data,
-                                RelExpr relExpr) const {
+RelExpr X86_64::adjustGotPcExpr(RelType type, int64_t addend,
+                                const uint8_t *loc) const {
   if (type != R_X86_64_GOTPCRELX && type != R_X86_64_REX_GOTPCRELX)
-    return relExpr;
-  const uint8_t op = data[-2];
-  const uint8_t modRm = data[-1];
+    return R_GOT_PC;
+  const uint8_t op = loc[-2];
+  const uint8_t modRm = loc[-1];
 
   // FIXME: When PIC is disabled and foo is defined locally in the
   // lower 32 bit address space, memory operand in mov can be converted into
   // immediate operand. Otherwise, mov must be changed to lea. We support only
   // latter relaxation at this moment.
   if (op == 0x8b)
     return R_RELAX_GOT_PC;
 
   // Relax call and jmp.
   if (op == 0xff && (modRm == 0x15 || modRm == 0x25))
     return R_RELAX_GOT_PC;
 
   // We don't support test/binop instructions without a REX prefix.
   if (type == R_X86_64_GOTPCRELX)
-    return relExpr;
+    return R_GOT_PC;
 
   // Relaxation of test, adc, add, and, cmp, or, sbb, sub, xor.
   // If PIC then no relaxation is available.
-  return config->isPic ? relExpr : R_RELAX_GOT_PC_NOPIC;
+  return config->isPic ? R_GOT_PC : R_RELAX_GOT_PC_NOPIC;
 }
 
 // A subset of relaxations can only be applied for no-PIC. This method
 // handles such relaxations. Instructions encoding information was taken from:
 // "Intel 64 and IA-32 Architectures Software Developer's Manual V2"
 // (http://www.intel.com/content/dam/www/public/us/en/documents/manuals/
 //    64-ia-32-architectures-software-developer-instruction-set-reference-manual-325383.pdf)
 static void relaxGotNoPic(uint8_t *loc, uint64_t val, uint8_t op,

lld/ELF/Relocations.cpp

static void scanReloc(InputSectionBase &sec, OffsetGetter &getOffset, RelTy *&i,
   //
   // If we know that a PLT entry will be resolved within the same ELF module, we
   // can skip PLT access and directly jump to the destination function. For
   // example, if we are linking a main executable, all dynamic symbols that can
   // be resolved within the executable will actually be resolved that way at
   // runtime, because the main executable is always at the beginning of a search
   // list. We can leverage that fact.
   if (!sym.isPreemptible && (!sym.isGnuIFunc() || config->zIfuncNoplt)) {
-    if (expr == R_GOT_PC && !isAbsoluteValue(sym)) {
-      expr = target->adjustRelaxExpr(type, relocatedAddr, expr);
-    } else {
+    if (expr != R_GOT_PC) {
       // The 0x8000 bit of r_addend of R_PPC_PLTREL24 is used to choose call
       // stub type. It should be ignored if optimized to R_PC.
       if (config->emachine == EM_PPC && expr == R_PPC32_PLTREL)
         addend &= ~0x8000;
       // R_HEX_GD_PLT_B22_PCREL (call a@GDPLT) is transformed into
       // call __tls_get_addr even if the symbol is non-preemptible.
       if (!(config->emachine == EM_HEXAGON &&
            (type == R_HEX_GD_PLT_B22_PCREL ||
             type == R_HEX_GD_PLT_B22_PCREL_X ||
             type == R_HEX_GD_PLT_B32_PCREL_X)))
       expr = fromPlt(expr);
+    } else if (!isAbsoluteValue(sym)) {
+      expr = target->adjustGotPcExpr(type, addend, relocatedAddr);
     }
   }
 
   // If the relocation does not emit a GOT or GOTPLT entry but its computation
   // uses their addresses, we need GOT or GOTPLT to be created.
   //
   // The 4 types that relative GOTPLT are all x86 and x86-64 specific.
   if (oneof<R_GOTPLTONLY_PC, R_GOTPLTREL, R_GOTPLT, R_TLSGD_GOTPLT>(expr)) {

lld/ELF/Target.h

public:
 
   // If a target needs to rewrite calls to __morestack to instead call
   // __morestack_non_split when a split-stack enabled caller calls a
   // non-split-stack callee this will return true. Otherwise returns false.
   bool needsMoreStackNonSplit = true;
 
   virtual RelExpr adjustRelaxExpr(RelType type, const uint8_t *data,
                                   RelExpr expr) const;
+  virtual RelExpr adjustGotPcExpr(RelType type, int64_t addend,
+                                  const uint8_t *loc) const;
   virtual void relaxGot(uint8_t *loc, const Relocation &rel,
                         uint64_t val) const;
   virtual void relaxTlsGdToIe(uint8_t *loc, const Relocation &rel,
                               uint64_t val) const;
   virtual void relaxTlsGdToLe(uint8_t *loc, const Relocation &rel,
                               uint64_t val) const;
   virtual void relaxTlsIeToLe(uint8_t *loc, const Relocation &rel,
                               uint64_t val) const;

lld/ELF/Target.cpp

bool TargetInfo::inBranchRange(RelType type, uint64_t src, uint64_t dst) const {
   return true;
 }
 
 RelExpr TargetInfo::adjustRelaxExpr(RelType type, const uint8_t *data,
                                     RelExpr expr) const {
   return expr;
 }
 
+RelExpr TargetInfo::adjustGotPcExpr(RelType type, int64_t addend,
+                                    const uint8_t *data) const {
+  return R_GOT_PC;
+}
+
 void TargetInfo::relaxGot(uint8_t *loc, const Relocation &rel,
                           uint64_t val) const {
   llvm_unreachable("Should not have claimed to be relaxable");
 }
 
 void TargetInfo::relaxTlsGdToLe(uint8_t *loc, const Relocation &rel,
                                 uint64_t val) const {
   llvm_unreachable("Should not have claimed to be relaxable");