Fix emission of _fltused for MSVC.

It should be emitted when any floating-point operations (including
calls) are present in the object, not just when calls to printf/scanf
with floating point args are made.

The difference caused by this is very subtle: in static (/MT) builds,
on x86-32, in a program that uses floating point but doesn't print it,
the default x87 rounding mode may not be set properly upon
initialization.

This commit also removes the walk of the types pointed to by pointer
arguments in calls. (To assist in opaque pointer types migration --
eventually the pointee type won't be available.)

That latter implies that it will no longer consider a call like
`scanf("%f", &floatvar)` as sufficient to emit _fltused on its
own. And without _fltused, `scanf("%f")` will abort with error R6002. This
new behavior is unlikely to bite anyone in practice (you'd have to
read a float, and do nothing with it!), and also, is consistent with
MSVC.

Differential Revision: https://reviews.llvm.org/D56548

llvm-svn: 352076

llvm/include/llvm/CodeGen/MachineModuleInfo.h

@@ -113,10 +113,9 @@ class MachineModuleInfo : public ImmutablePass {
   /// True if debugging information is available in this module.
   bool DbgInfoAvailable;
 
-  /// True if this module calls VarArg function with floating-point arguments.
-  /// This is used to emit an undefined reference to _fltused on Windows
-  /// targets.
-  bool UsesVAFloatArgument;
+  /// 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;
 
   /// True if the module calls the __morestack function indirectly, as is
   /// required under the large code model on x86. This is used to emit
@@ -186,13 +185,9 @@ class MachineModuleInfo : public ImmutablePass {
   bool hasDebugInfo() const { return DbgInfoAvailable; }
   void setDebugInfoAvailability(bool avail) { DbgInfoAvailable = avail; }
 
-  bool usesVAFloatArgument() const {
-    return UsesVAFloatArgument;
-  }
+  bool usesMSVCFloatingPoint() const { return UsesMSVCFloatingPoint; }
 
-  void setUsesVAFloatArgument(bool b) {
-    UsesVAFloatArgument = b;
-  }
+  void setUsesMSVCFloatingPoint(bool b) { UsesMSVCFloatingPoint = b; }
 
   bool usesMorestackAddr() const {
     return UsesMorestackAddr;
@@ -257,14 +252,6 @@ class MachineModuleInfo : public ImmutablePass {
   /// \}
 }; // End class MachineModuleInfo
 
-//===- MMI building helpers -----------------------------------------------===//
-
-/// Determine if any floating-point values are being passed to this variadic
-/// function, and set the MachineModuleInfo's usesVAFloatArgument flag if so.
-/// This flag is used to emit an undefined reference to _fltused on Windows,
-/// which will link in MSVCRT's floating-point support.
-void computeUsesVAFloatArgument(const CallInst &I, MachineModuleInfo &MMI);
-
 } // end namespace llvm
 
 #endif // LLVM_CODEGEN_MACHINEMODULEINFO_H

llvm/lib/CodeGen/MachineModuleInfo.cpp

@@ -205,7 +205,7 @@ MachineModuleInfo::~MachineModuleInfo() = default;
 bool MachineModuleInfo::doInitialization(Module &M) {
   ObjFileMMI = nullptr;
   CurCallSite = 0;
-  UsesVAFloatArgument = UsesMorestackAddr = false;
+  UsesMSVCFloatingPoint = UsesMorestackAddr = false;
   HasSplitStack = HasNosplitStack = false;
   AddrLabelSymbols = nullptr;
   TheModule = &M;
@@ -327,22 +327,3 @@ char FreeMachineFunction::ID;
 FunctionPass *llvm::createFreeMachineFunctionPass() {
   return new FreeMachineFunction();
 }
-
-//===- MMI building helpers -----------------------------------------------===//
-
-void llvm::computeUsesVAFloatArgument(const CallInst &I,
-                                      MachineModuleInfo &MMI) {
-  FunctionType *FT =
-      cast<FunctionType>(I.getCalledValue()->getType()->getContainedType(0));
-  if (FT->isVarArg() && !MMI.usesVAFloatArgument()) {
-    for (unsigned i = 0, e = I.getNumArgOperands(); i != e; ++i) {
-      Type *T = I.getArgOperand(i)->getType();
-      for (auto i : post_order(T)) {
-        if (i->isFloatingPointTy()) {
-          MMI.setUsesVAFloatArgument(true);
-          return;
-        }
-      }
-    }
-  }
-}

llvm/lib/CodeGen/SelectionDAG/FastISel.cpp

@@ -1303,9 +1303,6 @@ bool FastISel::selectCall(const User *I) {
     return true;
   }
 
-  MachineModuleInfo &MMI = FuncInfo.MF->getMMI();
-  computeUsesVAFloatArgument(*Call, MMI);
-
   // Handle intrinsic function calls.
   if (const auto *II = dyn_cast<IntrinsicInst>(Call))
     return selectIntrinsicCall(II);

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -6987,9 +6987,6 @@ void SelectionDAGBuilder::visitCall(const CallInst &I) {
     return;
   }
 
-  MachineModuleInfo &MMI = DAG.getMachineFunction().getMMI();
-  computeUsesVAFloatArgument(I, MMI);
-
   const char *RenameFn = nullptr;
   if (Function *F = I.getCalledFunction()) {
     if (F->isDeclaration()) {

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

@@ -41,6 +41,7 @@
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineMemOperand.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineOperand.h"
 #include "llvm/CodeGen/MachinePassRegistry.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
@@ -62,6 +63,7 @@
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/InlineAsm.h"
+#include "llvm/IR/InstIterator.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
@@ -378,6 +380,30 @@ static void SplitCriticalSideEffectEdges(Function &Fn, DominatorTree *DT,
   }
 }
 
+static void computeUsesMSVCFloatingPoint(const Triple &TT, const Function &F,
+                                         MachineModuleInfo &MMI) {
+  // Only needed for MSVC
+  if (!TT.isKnownWindowsMSVCEnvironment())
+    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;
+      }
+    }
+  }
+}
+
 bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
   // If we already selected that function, we do not need to run SDISel.
   if (mf.getProperties().hasProperty(
@@ -589,6 +615,9 @@ bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
   // Determine if there is a call to setjmp in the machine function.
   MF->setExposesReturnsTwice(Fn.callsFunctionThatReturnsTwice());
 
+  // Determine if floating point is used for msvc
+  computeUsesMSVCFloatingPoint(TM.getTargetTriple(), Fn, MF->getMMI());
+
   // Replace forward-declared registers with the registers containing
   // the desired value.
   MachineRegisterInfo &MRI = MF->getRegInfo();

llvm/lib/Target/X86/X86AsmPrinter.cpp

@@ -682,26 +682,31 @@ void X86AsmPrinter::EmitEndOfAsmFile(Module &M) {
     // stripping. Since LLVM never generates code that does this, it is always
     // safe to set.
     OutStreamer->EmitAssemblerFlag(MCAF_SubsectionsViaSymbols);
-    return;
-  }
-
-  if (TT.isKnownWindowsMSVCEnvironment() && MMI->usesVAFloatArgument()) {
-    StringRef SymbolName =
-        (TT.getArch() == Triple::x86_64) ? "_fltused" : "__fltused";
-    MCSymbol *S = MMI->getContext().getOrCreateSymbol(SymbolName);
-    OutStreamer->EmitSymbolAttribute(S, MCSA_Global);
-    return;
-  }
-
-  if (TT.isOSBinFormatCOFF()) {
+  } else if (TT.isOSBinFormatCOFF()) {
+    if (MMI->usesMSVCFloatingPoint()) {
+      // 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:
+      //
+      // 1. For x86-32, it will set the x87 rounding mode to 53-bit instead of
+      // 64-bit mantissas at program start.
+      //
+      // 2. It links in support routines for floating-point in scanf and printf.
+      //
+      // MSVC emits an undefined reference to _fltused when there are any
+      // floating point operations in the program (including calls). A program
+      // that only has: `scanf("%f", &global_float);` may fail to trigger this,
+      // but oh well...that's a documented issue.
+      StringRef SymbolName =
+          (TT.getArch() == Triple::x86) ? "__fltused" : "_fltused";
+      MCSymbol *S = MMI->getContext().getOrCreateSymbol(SymbolName);
+      OutStreamer->EmitSymbolAttribute(S, MCSA_Global);
+      return;
+    }
     emitStackMaps(SM);
-    return;
-  }
-
-  if (TT.isOSBinFormatELF()) {
+  } else if (TT.isOSBinFormatELF()) {
     emitStackMaps(SM);
     FM.serializeToFaultMapSection();
-    return;
   }
 }
 

llvm/test/CodeGen/X86/fltused.ll

@@ -1,6 +1,5 @@
-; The purpose of this test to verify that the fltused symbol is emitted when
-; any function is called with floating point arguments on Windows. And that it
-; is not emitted otherwise.
+; The purpose of this test to verify that the fltused symbol is
+; emitted when a floating point call is made on Windows.
 
 ; RUN: llc < %s -mtriple i686-pc-win32 | FileCheck %s --check-prefix WIN32
 ; RUN: llc < %s -mtriple x86_64-pc-win32 | FileCheck %s --check-prefix WIN64

llvm/test/CodeGen/X86/fltused_function_pointer.ll

@@ -1,6 +1,5 @@
-; The purpose of this test to verify that the fltused symbol is emitted when
-; any function is called with floating point arguments on Windows. And that it
-; is not emitted otherwise.
+; The purpose of this test to verify that the fltused symbol is
+; emitted when a floating point call is made on Windows.
 
 ; RUN: llc < %s -mtriple i686-pc-win32 | FileCheck %s --check-prefix WIN32
 ; RUN: llc < %s -mtriple x86_64-pc-win32 | FileCheck %s --check-prefix WIN64

llvm/test/CodeGen/X86/fltused_math.ll

@@ -0,0 +1,18 @@
+; The purpose of this test to verify that the fltused symbol is
+; emitted when floating point operations are used on Windows.
+
+; RUN: llc < %s -mtriple i686-pc-win32 | FileCheck %s --check-prefix WIN32
+; RUN: llc < %s -mtriple x86_64-pc-win32 | FileCheck %s --check-prefix WIN64
+; RUN: llc < %s -O0 -mtriple i686-pc-win32 | FileCheck %s --check-prefix WIN32
+; RUN: llc < %s -O0 -mtriple x86_64-pc-win32 | FileCheck %s --check-prefix WIN64
+
+define i32 @foo(i32 %a) nounwind {
+entry:
+  %da = sitofp i32 %a to double
+  %div = fdiv double %da, 3.100000e+00
+  %res = fptosi double %div to i32
+  ret i32 %res
+}
+
+; WIN32: .globl __fltused
+; WIN64: .globl _fltused