[GlobalIsel][X86] Support G_GLOBAL_VALUE for global stub references

llvm/lib/Target/X86/X86InstructionSelector.cpp

bool X86InstructionSelector::selectGlobalValue(MachineInstr &I,
   // Can't handle alternate code models yet.
   if (TM.getCodeModel() != CodeModel::Small)
     return false;
 
   X86AddressMode AM;
   AM.GV = GV;
   AM.GVOpFlags = STI.classifyGlobalReference(GV);
 
-  // TODO: The ABI requires an extra load. not supported yet.
-  if (isGlobalStubReference(AM.GVOpFlags))
-    return false;
+  if (isGlobalStubReference(AM.GVOpFlags)) {
+    unsigned Opc = 0;
+    X86AddressMode StubAM;
+    StubAM.Base.Reg = AM.Base.Reg;
+    StubAM.GV = GV;
+    StubAM.GVOpFlags = AM.GVOpFlags;
+    if (STI.getTargetLowering()->getPointerTy(MF.getDataLayout()) == MVT::i64) {
+      Opc = X86::MOV64rm;
+    } else {
+      Opc = X86::MOV32rm;
+    }
+
+    if (STI.isPICStyleRIPRel() || AM.GVOpFlags == X86II::MO_GOTPCREL ||
+        AM.GVOpFlags == X86II::MO_GOTPCREL_NORELAX)
+      StubAM.Base.Reg = X86::RIP;
+
+    I.setDesc(TII.get(Opc));
+    MachineInstrBuilder MIB(MF, I);
+
+    I.removeOperand(1);
+    addFullAddress(MIB, StubAM);
+    return constrainSelectedInstRegOperands(I, TII, TRI, RBI);
+  }
 
   // TODO: This reference is relative to the pic base. not supported yet.
   if (isGlobalRelativeToPICBase(AM.GVOpFlags))
     return false;
 
   if (STI.isPICStyleRIPRel()) {
     // Use rip-relative addressing.
     assert(AM.Base.Reg == 0 && AM.IndexReg == 0);

llvm/test/CodeGen/X86/GlobalISel/GV.ll

 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
 ; RUN: llc -mtriple=x86_64-linux-gnu    -global-isel -verify-machineinstrs                       < %s -o - | FileCheck %s --check-prefix=X64
 ; RUN: llc -mtriple=x86_64-apple-darwin -global-isel -verify-machineinstrs -relocation-model=pic < %s -o - | FileCheck %s --check-prefix=X64_DARWIN_PIC
 ; RUN: llc -mtriple=i386-linux-gnu      -global-isel -verify-machineinstrs                       < %s -o - | FileCheck %s --check-prefix=X32
 ; RUN: llc -mtriple=x86_64-linux-gnux32 -global-isel -verify-machineinstrs                       < %s -o - | FileCheck %s --check-prefix=X32ABI
 
 @g_int = dso_local global i32 0, align 4
+@g_int_stub = global i32 0, align 4
 
 ; Function Attrs: noinline nounwind optnone uwtable
 define dso_local ptr @test_global_ptrv() #3 {
 ; X64-LABEL: test_global_ptrv:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    leaq g_int, %rax
 ; X64-NEXT:    retq
 ;

 ; X32ABI-NEXT:    leal g_int, %eax
 ; X32ABI-NEXT:    movl (%eax), %eax
 ; X32ABI-NEXT:    retq
 entry:
   %0 = load i32, ptr @g_int, align 4
   ret i32 %0
 }
 
+define dso_local ptr @test_global_stub_ptrv() #3 {
+; X64-LABEL: test_global_stub_ptrv:
+; X64:       # %bb.0:
+; X64-NEXT:    movq g_int_stub@GOTPCREL(%rip), %rax
+; X64-NEXT:    retq
+;
+; X64_DARWIN_PIC-LABEL: test_global_stub_ptrv:
+; X64_DARWIN_PIC:       ## %bb.0:
+; X64_DARWIN_PIC-NEXT:    leaq _g_int_stub(%rip), %rax
+; X64_DARWIN_PIC-NEXT:    retq
+;
+; X32-LABEL: test_global_stub_ptrv:
+; X32:       # %bb.0:
+; X32-NEXT:    leal g_int_stub, %eax
+; X32-NEXT:    retl
+;
+; X32ABI-LABEL: test_global_stub_ptrv:
+; X32ABI:       # %bb.0:
+; X32ABI-NEXT:    movl g_int_stub@GOTPCREL(%rip), %eax
+; X32ABI-NEXT:    movl %eax, %eax
+; X32ABI-NEXT:    retq
+  ret ptr @g_int_stub
+}
+
+define dso_local i32 @test_global_stub_valv() #3 {
+; X64-LABEL: test_global_stub_valv:
+; X64:       # %bb.0: # %entry
+; X64-NEXT:    movq g_int_stub@GOTPCREL(%rip), %rax
+; X64-NEXT:    movl (%rax), %eax
+; X64-NEXT:    retq
+;
+; X64_DARWIN_PIC-LABEL: test_global_stub_valv:
+; X64_DARWIN_PIC:       ## %bb.0: ## %entry
+; X64_DARWIN_PIC-NEXT:    leaq _g_int_stub(%rip), %rax
+; X64_DARWIN_PIC-NEXT:    movl (%rax), %eax
+; X64_DARWIN_PIC-NEXT:    retq
+;
+; X32-LABEL: test_global_stub_valv:
+; X32:       # %bb.0: # %entry
+; X32-NEXT:    leal g_int_stub, %eax
+; X32-NEXT:    movl (%eax), %eax
+; X32-NEXT:    retl
+;
+; X32ABI-LABEL: test_global_stub_valv:
+; X32ABI:       # %bb.0: # %entry
+; X32ABI-NEXT:    movl g_int_stub@GOTPCREL(%rip), %eax
+; X32ABI-NEXT:    movl (%eax), %eax
+; X32ABI-NEXT:    retq
+entry:
+  %0 = load i32, ptr @g_int_stub, align 4
+  ret i32 %0
+}