[X86] Add support for llvm.thread.pointer

[• koriakin]

Summary

This will be used for __builtin_thread_pointer in clang.

[• koriakin]

Ping?

[reames]

This is missing documentation. It *looks* like you're trying to get the
thread local storage pointer. Is that correct? This can't be reviewed
without context and documented intent.

Philip

[• koriakin]

In D19582#421480, @reames wrote:

This is missing documentation. It *looks* like you're trying to get the
thread local storage pointer. Is that correct? This can't be reviewed
without context and documented intent.

Philip

This is indeed intended to fetch the TLS pointer: http://llvm.org/docs/LangRef.html#llvm-thread-pointer-intrinsic . For x86, this is simply the FS/GS base, ie. pointer to end of the TLS area. The intent is to support __builtin_thread_pointer() in clang, which comes useful in some strange places (eg. sanitizer_common uses it for aarch64, and could use it for x86 too if only gcc supported it as well).

[• koriakin]

Ping?

[bruno]

Hi Marcin,

Would this work for all x86 platforms? Is this supposed to be Linux specific? If so, lacks appropriate checking.

@Manman, would this work out-of-the-box for Darwin?

lib/Target/X86/X86ISelLowering.cpp

17827

What these constants mean? Please document it a comment

[majnemer]

lib/Target/X86/X86ISelLowering.cpp

17825

This isn't true for windows.

lib/Target/X86/X86ISelLowering.cpp

case Intrinsic::localaddress: {
     const X86RegisterInfo *RegInfo = Subtarget.getRegisterInfo();
     unsigned Reg;
     if (RegInfo->hasBasePointer(MF))
       Reg = RegInfo->getBaseRegister();
     else // This function handles the SP or FP case.
       Reg = RegInfo->getPtrSizedFrameRegister(MF);
     return DAG.getCopyFromReg(DAG.getEntryNode(), dl, Reg, VT);
   }
+
+  case Intrinsic::thread_pointer: {
+    const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+    EVT PtrVT = TLI.getPointerTy(DAG.getDataLayout());
+    // Get the Thread Pointer, which is %gs:0 (32-bit) or %fs:0 (64-bit).
+    Value *Ptr = Constant::getNullValue(
+        Type::getInt8PtrTy(*DAG.getContext(), Subtarget.is64Bit() ? 257 : 256));
+    return DAG.getLoad(PtrVT, dl, DAG.getEntryNode(),
+                       DAG.getIntPtrConstant(0, dl),
+                       MachinePointerInfo(Ptr), false, false, false, 0);
+  }
   }
 }
 
 static SDValue getGatherNode(unsigned Opc, SDValue Op, SelectionDAG &DAG,
                               SDValue Src, SDValue Mask, SDValue Base,
                               SDValue Index, SDValue ScaleOp, SDValue Chain,
                               const X86Subtarget &Subtarget) {
   SDLoc dl(Op);

test/CodeGen/X86/thread-pointer.ll

+; RUN: llc < %s -mtriple=i386-unknown-linux | FileCheck %s --check-prefix=CHECK-32
+; RUN: llc < %s -mtriple=x86_64-unknown-linux | FileCheck %s --check-prefix=CHECK-64
+
+; Function Attrs: nounwind readnone
+declare i8* @llvm.thread.pointer() #1
+
+define i8* @thread_pointer() {
+; CHECK-32: movl %gs:0, %eax
+; CHECK-64: movq %fs:0, %rax
+  %1 = tail call i8* @llvm.thread.pointer()
+  ret i8* %1
+}