[PATCH] D58336: [X86] Fix tls variable lowering issue with large code model

[LuoYuanke via Phabricator via llvm-commits]

LuoYuanke created this revision.
LuoYuanke added reviewers: craig.topper, rnk, annita.zhang.
Herald added a project: LLVM.

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.

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


Repository:
  rL LLVM

https://reviews.llvm.org/D58336

Files:
  lib/Target/X86/X86ISelDAGToDAG.cpp
  test/CodeGen/X86/code-model-elf.ll


Index: test/CodeGen/X86/code-model-elf.ll
===================================================================
--- test/CodeGen/X86/code-model-elf.ll
+++ test/CodeGen/X86/code-model-elf.ll
@@ -37,6 +37,8 @@
 @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
+ at thread_data = external thread_local global i32, align 4
+
 
 define dso_local i32* @lea_static_data() #0 {
 ; SMALL-STATIC-LABEL: lea_static_data:
@@ -373,6 +375,47 @@
   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 at 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 at 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 at 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 at 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 at 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 at 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}
Index: lib/Target/X86/X86ISelDAGToDAG.cpp
===================================================================
--- lib/Target/X86/X86ISelDAGToDAG.cpp
+++ lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -1137,15 +1137,23 @@
   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.


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