[X86] Teach fastisel to select calls to dllimport functions

[rnk]

Summary

Direct calls to dllimport functions are very common Windows. We should
add them to the -O0 fast path.

[rnk]

+more object file / relocation reviewers

[echristo]

In general looks ok. Mind commenting the if(NeedLoad) areas as to what you're adding on and why? The symbol is (IMO) obvious, but the random bits less so.

Thanks!

llvm/lib/Target/X86/X86FastISel.cpp

if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
     if (TM.getCodeModel() != CodeModel::Small)
       return false;
 
     // RIP-relative addresses can't have additional register operands.
     if (Subtarget->isPICStyleRIPRel() &&
         (AM.Base.Reg != 0 || AM.IndexReg != 0))
       return false;
 
-    // Can't handle DLL Import.
-    if (GV->hasDLLImportStorageClass())
-      return false;
-
     // Can't handle TLS.
     if (const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV))
       if (GVar->isThreadLocal())
         return false;
 
     // Okay, we've committed to selecting this global. Set up the basic address.
     AM.GV = GV;
 
-    // No ABI requires an extra load for anything other than DLLImport, which
-    // we rejected above. Return a direct reference to the global.
+    // Return a direct reference to the global. Fastisel can handle calls to
+    // functions that require loads, such as dllimport and nonlazybind
+    // functions.
     if (Subtarget->isPICStyleRIPRel()) {
       // Use rip-relative addressing if we can.  Above we verified that the
       // base and index registers are unused.
       assert(AM.Base.Reg == 0 && AM.IndexReg == 0);
       AM.Base.Reg = X86::RIP;
     } else {
       AM.GVOpFlags = Subtarget->classifyLocalReference(nullptr);
     }
bool X86FastISel::fastLowerCall(CallLoweringInfo &CLI) {
   if (CalleeOp) {
     // Register-indirect call.
     unsigned CallOpc = Is64Bit ? X86::CALL64r : X86::CALL32r;
     MIB = BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, TII.get(CallOpc))
       .addReg(CalleeOp);
   } else {
     // Direct call.
     assert(GV && "Not a direct call");
-    unsigned CallOpc = Is64Bit ? X86::CALL64pcrel32 : X86::CALLpcrel32;
-
     // See if we need any target-specific flags on the GV operand.
     unsigned char OpFlags = Subtarget->classifyGlobalFunctionReference(GV);
     // Ignore NonLazyBind attribute in FastISel
     if (OpFlags == X86II::MO_GOTPCREL)
       OpFlags = 0;
 
+    // This will be a direct call, or an indirect call through memory for
+    // NonLazyBind calls or dllimport calls.
+    bool NeedLoad = OpFlags == X86II::MO_DLLIMPORT;
+    unsigned CallOpc = NeedLoad
+                           ? (Is64Bit ? X86::CALL64m : X86::CALL32m)
+                           : (Is64Bit ? X86::CALL64pcrel32 : X86::CALLpcrel32);
+
     MIB = BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, TII.get(CallOpc));
+    if (NeedLoad)
+      MIB.addReg(Is64Bit ? X86::RIP : 0).addImm(1).addReg(0);
     if (Symbol)
       MIB.addSym(Symbol, OpFlags);
     else
       MIB.addGlobalAddress(GV, 0, OpFlags);
+    if (NeedLoad)
+      MIB.addReg(0);
   }
 
   // Add a register mask operand representing the call-preserved registers.
   // Proper defs for return values will be added by setPhysRegsDeadExcept().
   MIB.addRegMask(TRI.getCallPreservedMask(*FuncInfo.MF, CC));
 
   // Add an implicit use GOT pointer in EBX.
   if (Subtarget->isPICStyleGOT())

llvm/lib/Target/X86/X86Subtarget.cpp

 }
 
 unsigned char
 X86Subtarget::classifyGlobalFunctionReference(const GlobalValue *GV,
                                               const Module &M) const {
   if (TM.shouldAssumeDSOLocal(M, GV))
     return X86II::MO_NO_FLAG;
 
-  assert(!isTargetCOFF());
+  if (isTargetCOFF()) {
+    assert(GV->hasDLLImportStorageClass() &&
+           "shouldAssumeDSOLocal gave inconsistent answer");
+    return X86II::MO_DLLIMPORT;
+  }
+
   const Function *F = dyn_cast_or_null<Function>(GV);
 
   if (isTargetELF()) {
     if (is64Bit() && F && (CallingConv::X86_RegCall == F->getCallingConv()))
       // According to psABI, PLT stub clobbers XMM8-XMM15.
       // In Regcall calling convention those registers are used for passing
       // parameters. Thus we need to prevent lazy binding in Regcall.
       return X86II::MO_GOTPCREL;

llvm/test/CodeGen/X86/dllimport-x86_64.ll

 ; RUN: llc -mtriple x86_64-pc-win32 < %s | FileCheck %s
 ; RUN: llc -mtriple x86_64-pc-mingw32 < %s | FileCheck %s
 ;
-; RUN: llc -mtriple x86_64-pc-mingw32 -O0 < %s | FileCheck %s -check-prefix=FAST
+; RUN: llc -mtriple x86_64-pc-mingw32 -O0 < %s | FileCheck %s
+; RUN: llc -mtriple x86_64-pc-windows-msvc -O0 < %s | FileCheck %s
 ; PR6275
 ;
 ; RUN: opt -mtriple x86_64-pc-win32 -O3 -S < %s | FileCheck %s -check-prefix=OPT
 
 @Var1 = external dllimport global i32
 @Var2 = available_externally dllimport unnamed_addr constant i32 1
 
 declare dllimport void @fun()
 
 define available_externally dllimport void @inline1() {
   ret void
 }
 
 define available_externally dllimport void @inline2() {
   ret void
 }
 
 declare void @dummy(...)
 
 define void @use() nounwind {
 ; CHECK:     callq *__imp_fun(%rip)
-; FAST:      movq  __imp_fun(%rip), [[R:%[a-z]{3}]]
-; FAST-NEXT: callq *[[R]]
   call void @fun()
 
 ; CHECK: callq *__imp_inline1(%rip)
 ; CHECK: callq *__imp_inline2(%rip)
   call void @inline1()
   call void @inline2()
 
 ; available_externally uses go away

llvm/test/CodeGen/X86/dllimport.ll

 ; RUN: llc -mtriple i386-pc-win32 < %s | FileCheck %s
 ; RUN: llc -mtriple i386-pc-mingw32 < %s | FileCheck %s
 ;
-; RUN: llc -mtriple i386-pc-mingw32 -O0 < %s | FileCheck %s -check-prefix=FAST
+; RUN: llc -mtriple i386-pc-mingw32 -O0 < %s | FileCheck %s
+; RUN: llc -mtriple i386-pc-windows-msvc -O0 < %s | FileCheck %s
 ; PR6275
 ;
 ; RUN: opt -mtriple i386-pc-win32 -O3 -S < %s | FileCheck %s -check-prefix=OPT
 
 @Var1 = external dllimport global i32
 @Var2 = available_externally dllimport unnamed_addr constant i32 1
 
 declare dllimport void @fun()

 declare dllimport x86_stdcallcc void @stdfun() nounwind
 declare dllimport x86_fastcallcc void @fastfun() nounwind
 declare dllimport x86_thiscallcc void @thisfun() nounwind
 
 declare void @dummy(...)
 
 define void @use() nounwind {
 ; CHECK:     calll *__imp__fun
-; FAST:      movl  __imp__fun, [[R:%[a-z]{3}]]
-; FAST-NEXT: calll *[[R]]
   call void @fun()
 
 ; CHECK: calll *__imp__inline1
 ; CHECK: calll *__imp__inline2
   call void @inline1()
   call void @inline2()
 
 ; CHECK: calll *__imp__stdfun@0

llvm/test/CodeGen/X86/fast-isel-call-cleanup.ll

+; RUN: llc -fast-isel -O0 -code-model=large -mcpu=generic -mtriple=x86_64-apple-darwin10 -relocation-model=pic < %s | FileCheck %s
+
+; Check that fast-isel cleans up when it fails to lower a call instruction.
+define void @fastiselcall() {
+entry:
+  %call = call i32 @targetfn(i32 42)
+  ret void
+; CHECK-LABEL: test5:
+; Local value area is still there:
+; CHECK: movl $42, {{%[a-z]+}}
+; Fast-ISel's arg mov is not here:
+; CHECK-NOT: movl $42, (%esp)
+; SDag-ISel's arg mov:
+; CHECK: movabsq $_targetfn, %[[REG:[^ ]*]]
+; CHECK: movl $42, %edi
+; CHECK: callq *%[[REG]]
+
+}
+declare i32 @targetfn(i32)

llvm/test/CodeGen/X86/fast-isel-x86.ll

entry:
   ret void
 ; CHECK-LABEL: test4:
 ; CHECK: subl $28
 ; CHECK: movl %esp, %ecx
 ; CHECK: calll _test4fastccsret
 ; CHECK: addl $28
 }
 declare fastcc void @test4fastccsret(%struct.a* sret)
-
-
-; Check that fast-isel cleans up when it fails to lower a call instruction.
-define void @test5() {
-entry:
-  %call = call i32 @test5dllimport(i32 42)
-  ret void
-; CHECK-LABEL: test5:
-; Local value area is still there:
-; CHECK: movl $42, {{%[a-z]+}}
-; Fast-ISel's arg push is not here:
-; CHECK-NOT: movl $42, (%esp)
-; SDag-ISel's arg push:
-; CHECK: movl %esp, [[REGISTER:%[a-z]+]]
-; CHECK: movl $42, ([[REGISTER]])
-; CHECK: movl L_test5dllimport$non_lazy_ptr-L8$pb(%eax), %eax
-
-}
-declare dllimport i32 @test5dllimport(i32)