[X86] Avoid data16 prefix for lea in x32 mode

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.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D93157

Author: hvdijk

llvm/lib/Target/X86/X86MCInstLower.cpp

@@ -979,6 +979,8 @@ void X86AsmPrinter::LowerTlsAddr(X86MCInstLower &MCInstLowering,
   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;
@@ -1012,7 +1014,7 @@ void X86AsmPrinter::LowerTlsAddr(X86MCInstLower &MCInstLowering,
 
   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)

llvm/test/CodeGen/X86/pic.ll

@@ -285,6 +285,7 @@ entry:
 ; 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