IRGen: Move vtable load after argument evaluation.

This change reduces the live range of the loaded function pointer,
resulting in a slight code size decrease (~10KB in clang), and also
improves the security of CFI for virtual calls by making it less
likely that the function pointer will be spilled, and ensuring that
it is not spilled across a function call boundary.

Fixes PR35353.

Differential Revision: https://reviews.llvm.org/D42725

llvm-svn: 324286

1 files changed, 18 insertions, 23 deletions

diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 420d2843af8..046acd76ce7 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -285,9 +285,9 @@ public:
   llvm::GlobalVariable *getAddrOfVTable(const CXXRecordDecl *RD,
                                         CharUnits VPtrOffset) override;
 
-  CGCallee getVirtualFunctionPointer(CodeGenFunction &CGF, GlobalDecl GD,
-                                     Address This, llvm::Type *Ty,
-                                     SourceLocation Loc) override;
+  llvm::Value *getVirtualFunctionPointer(CodeGenFunction &CGF, GlobalDecl GD,
+                                         Address This, llvm::Type *Ty,
+                                         SourceLocation Loc) override;
 
   llvm::Value *EmitVirtualDestructorCall(CodeGenFunction &CGF,
                                          const CXXDestructorDecl *Dtor,
@@ -1827,11 +1827,11 @@ llvm::GlobalVariable *MicrosoftCXXABI::getAddrOfVTable(const CXXRecordDecl *RD,
   return VTable;
 }
 
-CGCallee MicrosoftCXXABI::getVirtualFunctionPointer(CodeGenFunction &CGF,
-                                                    GlobalDecl GD,
-                                                    Address This,
-                                                    llvm::Type *Ty,
-                                                    SourceLocation Loc) {
+llvm::Value *MicrosoftCXXABI::getVirtualFunctionPointer(CodeGenFunction &CGF,
+                                                        GlobalDecl GD,
+                                                        Address This,
+                                                        llvm::Type *Ty,
+                                                        SourceLocation Loc) {
   GD = GD.getCanonicalDecl();
   CGBuilderTy &Builder = CGF.Builder;
 
@@ -1858,22 +1858,17 @@ CGCallee MicrosoftCXXABI::getVirtualFunctionPointer(CodeGenFunction &CGF,
         ->ObjectWithVPtr;
   };
 
-  llvm::Value *VFunc;
-  if (CGF.ShouldEmitVTableTypeCheckedLoad(MethodDecl->getParent())) {
-    VFunc = CGF.EmitVTableTypeCheckedLoad(
+  if (CGF.ShouldEmitVTableTypeCheckedLoad(MethodDecl->getParent()))
+    return CGF.EmitVTableTypeCheckedLoad(
         getObjectWithVPtr(), VTable,
         ML.Index * CGM.getContext().getTargetInfo().getPointerWidth(0) / 8);
-  } else {
-    if (CGM.getCodeGenOpts().PrepareForLTO)
-      CGF.EmitTypeMetadataCodeForVCall(getObjectWithVPtr(), VTable, Loc);
 
-    llvm::Value *VFuncPtr =
-        Builder.CreateConstInBoundsGEP1_64(VTable, ML.Index, "vfn");
-    VFunc = Builder.CreateAlignedLoad(VFuncPtr, CGF.getPointerAlign());
-  }
+  if (CGM.getCodeGenOpts().PrepareForLTO)
+    CGF.EmitTypeMetadataCodeForVCall(getObjectWithVPtr(), VTable, Loc);
 
-  CGCallee Callee(MethodDecl, VFunc);
-  return Callee;
+  llvm::Value *VFuncPtr =
+      Builder.CreateConstInBoundsGEP1_64(VTable, ML.Index, "vfn");
+  return Builder.CreateAlignedLoad(VFuncPtr, CGF.getPointerAlign());
 }
 
 llvm::Value *MicrosoftCXXABI::EmitVirtualDestructorCall(
@@ -1887,9 +1882,9 @@ llvm::Value *MicrosoftCXXABI::EmitVirtualDestructorCall(
   GlobalDecl GD(Dtor, Dtor_Deleting);
   const CGFunctionInfo *FInfo = &CGM.getTypes().arrangeCXXStructorDeclaration(
       Dtor, StructorType::Deleting);
-  llvm::Type *Ty = CGF.CGM.getTypes().GetFunctionType(*FInfo);
-  CGCallee Callee = getVirtualFunctionPointer(
-      CGF, GD, This, Ty, CE ? CE->getLocStart() : SourceLocation());
+  auto *Ty =
+      cast<llvm::FunctionType>(CGF.CGM.getTypes().GetFunctionType(*FInfo));
+  CGCallee Callee = CGCallee::forVirtual(CE, GD, This, Ty);
 
   ASTContext &Context = getContext();
   llvm::Value *ImplicitParam = llvm::ConstantInt::get(