1 files changed, 30 insertions, 2 deletions
diff --git a/llvm/lib/Target/X86/X86AsmPrinter.cpp b/llvm/lib/Target/X86/X86AsmPrinter.cpp
index 0c2c6bf7f8b7..f01e47b41cf5 100644
--- a/llvm/lib/Target/X86/X86AsmPrinter.cpp
+++ b/llvm/lib/Target/X86/X86AsmPrinter.cpp
@@ -28,6 +28,7 @@
 #include "llvm/CodeGenTypes/MachineValueType.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/InlineAsm.h"
+#include "llvm/IR/InstIterator.h"
 #include "llvm/IR/Mangler.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
@@ -975,6 +976,33 @@ static void emitNonLazyStubs(MachineModuleInfo *MMI, MCStreamer &OutStreamer) {
   }
 }
 
+/// True if this module is being built for windows/msvc, and uses floating
+/// point. This is used to emit an undefined reference to _fltused. This is
+/// needed in Windows kernel or driver contexts to find and prevent code from
+/// modifying non-GPR registers.
+///
+/// TODO: It would be better if this was computed from MIR by looking for
+/// selected floating-point instructions.
+static bool usesMSVCFloatingPoint(const Triple &TT, const Module &M) {
+  // Only needed for MSVC
+  if (!TT.isWindowsMSVCEnvironment())
+    return false;
+
+  for (const Function &F : M) {
+    for (const Instruction &I : instructions(F)) {
+      if (I.getType()->isFPOrFPVectorTy())
+        return true;
+
+      for (const auto &Op : I.operands()) {
+        if (Op->getType()->isFPOrFPVectorTy())
+          return true;
+      }
+    }
+  }
+
+  return false;
+}
+
 void X86AsmPrinter::emitEndOfAsmFile(Module &M) {
   const Triple &TT = TM.getTargetTriple();
 
@@ -993,7 +1021,7 @@ void X86AsmPrinter::emitEndOfAsmFile(Module &M) {
     // safe to set.
     OutStreamer->emitAssemblerFlag(MCAF_SubsectionsViaSymbols);
   } else if (TT.isOSBinFormatCOFF()) {
-    if (MMI->usesMSVCFloatingPoint()) {
+    if (usesMSVCFloatingPoint(TT, M)) {
       // In Windows' libcmt.lib, there is a file which is linked in only if the
       // symbol _fltused is referenced. Linking this in causes some
       // side-effects:
@@ -1039,7 +1067,7 @@ void X86AsmPrinter::emitEndOfAsmFile(Module &M) {
 //===----------------------------------------------------------------------===//
 
 // Force static initialization.
-extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeX86AsmPrinter() {
+extern "C" LLVM_C_ABI void LLVMInitializeX86AsmPrinter() {
   RegisterAsmPrinter<X86AsmPrinter> X(getTheX86_32Target());
   RegisterAsmPrinter<X86AsmPrinter> Y(getTheX86_64Target());
 }