[X86] Fix tls variable lowering issue with large code model

[LuoYuanke]

Summary

The problem here is the lowering for tls variable. Below is the DAG for the code.
SelectionDAG has 11 nodes:

t0: ch = EntryToken
      t8: i64,ch = load<(load 8 from `i8 addrspace(257)* null`, addrspace 257)> t0, Constant:i64<0>, undef:i64
        t10: i64 = X86ISD::WrapperRIP TargetGlobalTLSAddress:i64<i32* @x> 0 [TF=10]
      t11: i64,ch = load<(load 8 from got)> t0, t10, undef:i64
    t12: i64 = add t8, t11
  t4: i32,ch = load<(dereferenceable load 4 from @x)> t0, t12, undef:i64
t6: ch = CopyToReg t0, Register:i32 %0, t4

And when mcmodel is large, below instruction can NOT be folded.

  t10: i64 = X86ISD::WrapperRIP TargetGlobalTLSAddress:i64<i32* @x> 0 [TF=10]
t11: i64,ch = load<(load 8 from got)> t0, t10, undef:i64

So "t11: i64,ch = load<(load 8 from got)> t0, t10, undef:i64" is lowered to " Morphed node: t11: i64,ch = MOV64rm<Mem:(load 8 from got)> t10, TargetConstant:i8<1>, Register:i64 $noreg, TargetConstant:i32<0>, Register:i32 $noreg, t0"

When llvm start to lower "t10: i64 = X86ISD::WrapperRIP TargetGlobalTLSAddress:i64<i32* @x> 0 [TF=10]", it fails.

My patch is to fold the load and X86ISD::WrapperRIP.

[craig.topper]

It looks like this review was not subscribed to llvm-commits when it was created. This prevents the general mailing list from being notified of its existence. Can you abandon this and submit a new review with llvm-commits subscribed from the start?

It's also helpful to start reviews with a tag like "[X86]" that indicates the area of the compiler you're changing. It helps potentially interested people search through the many emails on llvm-commits and find the things they might be interested in.

[LuoYuanke]

Thanks. I abandon the review and create a new review at https://reviews.llvm.org/D58336.

lib/Target/X86/X86ISelDAGToDAG.cpp

 /// mode. These wrap things that will resolve down into a symbol reference.
 /// If no match is possible, this returns true, otherwise it returns false.
 bool X86DAGToDAGISel::matchWrapper(SDValue N, X86ISelAddressMode &AM) {
   // If the addressing mode already has a symbol as the displacement, we can
   // never match another symbol.
   if (AM.hasSymbolicDisplacement())
     return true;
 
+  bool IsRIPRelTLS = false;
   bool IsRIPRel = N.getOpcode() == X86ISD::WrapperRIP;
+  if (IsRIPRel) {
+    SDValue Val = N.getOperand(0);
+    if (Val.getOpcode() == ISD::TargetGlobalTLSAddress)
+      IsRIPRelTLS = true;
+  }
 
-  // We can't use an addressing mode in the 64-bit large code model. In the
-  // medium code model, we use can use an mode when RIP wrappers are present.
-  // That signifies access to globals that are known to be "near", such as the
-  // GOT itself.
+  // We can't use an addressing mode in the 64-bit large code model.
+  // Global TLS addressing is an exception. In the medium code model,
+  // we use can use an mode when RIP wrappers are present.
+  // That signifies access to globals that are known to be "near",
+  // such as the GOT itself.
   CodeModel::Model M = TM.getCodeModel();
   if (Subtarget->is64Bit() &&
-      (M == CodeModel::Large || (M == CodeModel::Medium && !IsRIPRel)))
+      ((M == CodeModel::Large && !IsRIPRelTLS) ||
+       (M == CodeModel::Medium && !IsRIPRel)))
     return true;
 
   // Base and index reg must be 0 in order to use %rip as base.
   if (IsRIPRel && AM.hasBaseOrIndexReg())
     return true;
 
   // Make a local copy in case we can't do this fold.
   X86ISelAddressMode Backup = AM;

test/CodeGen/X86/code-model-elf.ll

 ; ModuleID = 'model.c'
 source_filename = "model.c"
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64--linux"
 
 @global_data = dso_local global [10 x i32] [i32 1, i32 2, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0], align 16
 @static_data = internal global [10 x i32] zeroinitializer, align 16
 @extern_data = external global [10 x i32], align 16
+@thread_data = external thread_local global i32, align 4
+
 
 define dso_local i32* @lea_static_data() #0 {
 ; SMALL-STATIC-LABEL: lea_static_data:
 ; SMALL-STATIC:       # %bb.0:
 ; SMALL-STATIC-NEXT:    movl $static_data, %eax
 ; SMALL-STATIC-NEXT:    retq
 ;
 ; MEDIUM-STATIC-LABEL: lea_static_data:

 ; LARGE-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L9$pb, %rcx
 ; LARGE-PIC-NEXT:    addq %rax, %rcx
 ; LARGE-PIC-NEXT:    movabsq $extern_fn@GOT, %rax
 ; LARGE-PIC-NEXT:    movq (%rcx,%rax), %rax
 ; LARGE-PIC-NEXT:    retq
   ret void ()* @extern_fn
 }
 
+define dso_local i32 @load_thread_data() #0 {
+; SMALL-STATIC-LABEL: load_thread_data:
+; SMALL-STATIC:       # %bb.0:
+; SMALL-STATIC-NEXT:    movq    thread_data@GOTTPOFF(%rip), %rax
+; SMALL-STATIC-NEXT:    movl    %fs:(%rax), %eax
+; SMALL-STATIC-NEXT:    retq
+;
+; MEDIUM-STATIC-LABEL: load_thread_data:
+; MEDIUM-STATIC:       # %bb.0:
+; MEDIUM-STATIC-NEXT:    movq    thread_data@GOTTPOFF(%rip), %rax
+; MEDIUM-STATIC-NEXT:    movl    %fs:(%rax), %eax
+; MEDIUM-STATIC-NEXT:    retq
+;
+; LARGE-STATIC-LABEL: load_thread_data:
+; LARGE-STATIC:       # %bb.0:
+; LARGE-STATIC-NEXT:    movq    thread_data@GOTTPOFF(%rip), %rax
+; LARGE-STATIC-NEXT:    movl    %fs:(%rax), %eax
+; LARGE-STATIC-NEXT:    retq
+;
+; SMALL-PIC-LABEL: load_thread_data:
+; SMALL-PIC:       # %bb.0:
+; SMALL-PIC-NEXT:    movq    thread_data@GOTTPOFF(%rip), %rax
+; SMALL-PIC-NEXT:    movl    %fs:(%rax), %eax
+; SMALL-PIC-NEXT:    retq
+;
+; MEDIUM-PIC-LABEL: load_thread_data:
+; MEDIUM-PIC:       # %bb.0:
+; MEDIUM-PIC-NEXT:    movq    thread_data@GOTTPOFF(%rip), %rax
+; MEDIUM-PIC-NEXT:    movl    %fs:(%rax), %eax
+; MEDIUM-PIC-NEXT:    retq
+;
+; LARGE-PIC-LABEL: load_thread_data:
+; LARGE-PIC:       # %bb.0:
+; LARGE-PIC-NEXT:    movq    thread_data@GOTTPOFF(%rip), %rax
+; LARGE-PIC-NEXT:    movl    %fs:(%rax), %eax
+; LARGE-PIC-NEXT:    retq
+;
+  %1 = load i32, i32* @thread_data, align 4
+  ret i32 %1
+}
+
 attributes #0 = { noinline nounwind uwtable }
 
 !llvm.module.flags = !{!0, !1, !2}
 !llvm.ident = !{!3}
 
 !0 = !{i32 1, !"wchar_size", i32 4}
 !1 = !{i32 7, !"PIC Level", i32 2}
 !2 = !{i32 7, !"PIE Level", i32 2}
 !3 = !{!"clang version 7.0.0 "}