CodeGen: Remove UsesMSVCFloatingPoint from MachineModuleInfo

llvm/include/llvm/CodeGen/MachineModuleInfo.h

@@ -116,10 +116,6 @@ class MachineModuleInfo {
   /// True if debugging information is available in this module.
   bool DbgInfoAvailable = false;
 
-  /// True if this module is being built for windows/msvc, and uses floating
-  /// point.  This is used to emit an undefined reference to _fltused.
-  bool UsesMSVCFloatingPoint = false;
-
   /// Maps IR Functions to their corresponding MachineFunctions.
   DenseMap<const Function*, std::unique_ptr<MachineFunction>> MachineFunctions;
   /// Next unique number available for a MachineFunction.
@@ -189,10 +185,6 @@ class MachineModuleInfo {
   /// Returns true if valid debug info is present.
   bool hasDebugInfo() const { return DbgInfoAvailable; }
 
-  bool usesMSVCFloatingPoint() const { return UsesMSVCFloatingPoint; }
-
-  void setUsesMSVCFloatingPoint(bool b) { UsesMSVCFloatingPoint = b; }
-
   /// \name Exception Handling
   /// \{
 

llvm/lib/CodeGen/MachineModuleInfo.cpp

@@ -28,7 +28,6 @@ void MachineModuleInfo::initialize() {
   ObjFileMMI = nullptr;
   CurCallSite = 0;
   NextFnNum = 0;
-  UsesMSVCFloatingPoint = false;
   DbgInfoAvailable = false;
 }
 

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

@@ -417,30 +417,6 @@ void SelectionDAGISelLegacy::getAnalysisUsage(AnalysisUsage &AU) const {
   MachineFunctionPass::getAnalysisUsage(AU);
 }
 
-static void computeUsesMSVCFloatingPoint(const Triple &TT, const Function &F,
-                                         MachineModuleInfo &MMI) {
-  // Only needed for MSVC
-  if (!TT.isWindowsMSVCEnvironment())
-    return;
-
-  // If it's already set, nothing to do.
-  if (MMI.usesMSVCFloatingPoint())
-    return;
-
-  for (const Instruction &I : instructions(F)) {
-    if (I.getType()->isFPOrFPVectorTy()) {
-      MMI.setUsesMSVCFloatingPoint(true);
-      return;
-    }
-    for (const auto &Op : I.operands()) {
-      if (Op->getType()->isFPOrFPVectorTy()) {
-        MMI.setUsesMSVCFloatingPoint(true);
-        return;
-      }
-    }
-  }
-}
-
 PreservedAnalyses
 SelectionDAGISelPass::run(MachineFunction &MF,
                           MachineFunctionAnalysisManager &MFAM) {
@@ -802,9 +778,6 @@ bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
     }
   }
 
-  // Determine if floating point is used for msvc
-  computeUsesMSVCFloatingPoint(TM.getTargetTriple(), Fn, *CurDAG->getMMI());
-
   // Release function-specific state. SDB and CurDAG are already cleared
   // at this point.
   FuncInfo->clear();

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: