[X86] Avoid data16 prefix for lea in x32 mode

[hvdijk]

Summary

The ABI demands a data16 prefix for lea in 64-bit LP64 mode, but not in
64-bit ILP32 mode. In both modes this prefix would ordinarily be
ignored, but the instructions may be changed by the linker to
instructions that are affected by the prefix.

[RKSimon]

LGTM

llvm/lib/Target/X86/X86MCInstLower.cpp

void X86MCInstLower::Lower(const MachineInstr *MI, MCInst &OutMI) const {
   }
 }
 
 void X86AsmPrinter::LowerTlsAddr(X86MCInstLower &MCInstLowering,
                                  const MachineInstr &MI) {
   NoAutoPaddingScope NoPadScope(*OutStreamer);
   bool Is64Bits = MI.getOpcode() != X86::TLS_addr32 &&
                   MI.getOpcode() != X86::TLS_base_addr32;
+  bool Is64BitsLP64 = MI.getOpcode() == X86::TLS_addr64 ||
+                      MI.getOpcode() == X86::TLS_base_addr64;
   MCContext &Ctx = OutStreamer->getContext();
 
   MCSymbolRefExpr::VariantKind SRVK;
   switch (MI.getOpcode()) {
   case X86::TLS_addr32:
   case X86::TLS_addr64:
   case X86::TLS_addrX32:
     SRVK = MCSymbolRefExpr::VK_TLSGD;
void X86AsmPrinter::LowerTlsAddr(X86MCInstLower &MCInstLowering,
   // attempted to be relaxed to IE/LE (binutils PR24784). Work around the bug by
   // only using GOT when GOTPCRELX is enabled.
   // TODO Delete the workaround when GOTPCRELX becomes commonplace.
   bool UseGot = MMI->getModule()->getRtLibUseGOT() &&
                 Ctx.getAsmInfo()->canRelaxRelocations();
 
   if (Is64Bits) {
     bool NeedsPadding = SRVK == MCSymbolRefExpr::VK_TLSGD;
-    if (NeedsPadding)
+    if (NeedsPadding && Is64BitsLP64)
       EmitAndCountInstruction(MCInstBuilder(X86::DATA16_PREFIX));
     EmitAndCountInstruction(MCInstBuilder(X86::LEA64r)
                                 .addReg(X86::RDI)
                                 .addReg(X86::RIP)
                                 .addImm(1)
                                 .addReg(0)
                                 .addExpr(Sym)
                                 .addReg(0));

llvm/test/CodeGen/X86/pic.ll

 ; CHECK-I686-NEXT:  popl
 ; CHECK-I686: addl  $_GLOBAL_OFFSET_TABLE_+(.L{{.*}}-.L8$pb), %ebx
 ; CHECK-I686-DAG: leal  tlsdstgd@TLSGD(,%ebx), %eax
 ; CHECK-I686-DAG: calll ___tls_get_addr@PLT
 ; CHECK-I686-DAG: leal  tlsptrgd@TLSGD(,%ebx), %eax
 ; CHECK-I686-DAG: calll ___tls_get_addr@PLT
 ; CHECK-I686-DAG: leal  tlssrcgd@TLSGD(,%ebx), %eax
 ; CHECK-I686-DAG: calll ___tls_get_addr@PLT
+; CHECK-X32-NOT:  data16
 ; CHECK-X32-DAG:  leaq  tlsdstgd@TLSGD(%rip), %rdi
 ; CHECK-X32-DAG:  callq __tls_get_addr@PLT
 ; CHECK-X32-DAG:  leaq  tlsptrgd@TLSGD(%rip), %rdi
 ; CHECK-X32-DAG:  callq __tls_get_addr@PLT
 ; CHECK-X32-DAG:  leaq  tlssrcgd@TLSGD(%rip), %rdi
 ; CHECK-X32-DAG:  callq __tls_get_addr@PLT
 ; CHECK-I686: ret
 ; CHECK-X32:  retq