[CodeGen] Remove useless zero-index constant GEPs (NFCI)

Remove zero-index constant expression GEPs, which are not needed
with opaque pointers and will get folded away.

Author: nikic

clang/lib/CodeGen/CGBuiltin.cpp

@@ -5978,11 +5978,7 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
     auto Name = CGM.getCUDARuntime().getDeviceSideName(
         cast<DeclRefExpr>(E->getArg(0)->IgnoreImpCasts())->getDecl());
     auto Str = CGM.GetAddrOfConstantCString(Name, "");
-    llvm::Constant *Zeros[] = {llvm::ConstantInt::get(SizeTy, 0),
-                               llvm::ConstantInt::get(SizeTy, 0)};
-    auto *Ptr = llvm::ConstantExpr::getGetElementPtr(Str.getElementType(),
-                                                     Str.getPointer(), Zeros);
-    return RValue::get(Ptr);
+    return RValue::get(Str.getPointer());
   }
   }
 

clang/lib/CodeGen/CGCUDANV.cpp

@@ -71,8 +71,6 @@ class CGNVCUDARuntime : public CGCUDARuntime {
   bool RelocatableDeviceCode;
   /// Mangle context for device.
   std::unique_ptr<MangleContext> DeviceMC;
-  /// Some zeros used for GEPs.
-  llvm::Constant *Zeros[2];
 
   llvm::FunctionCallee getSetupArgumentFn() const;
   llvm::FunctionCallee getLaunchFn() const;
@@ -91,9 +89,7 @@ class CGNVCUDARuntime : public CGCUDARuntime {
   /// where the C code specifies const char*.
   llvm::Constant *makeConstantString(const std::string &Str,
                                      const std::string &Name = "") {
-    auto ConstStr = CGM.GetAddrOfConstantCString(Str, Name.c_str());
-    return llvm::ConstantExpr::getGetElementPtr(ConstStr.getElementType(),
-                                                ConstStr.getPointer(), Zeros);
+    return CGM.GetAddrOfConstantCString(Str, Name.c_str()).getPointer();
   }
 
   /// Helper function which generates an initialized constant array from Str,
@@ -117,7 +113,7 @@ class CGNVCUDARuntime : public CGCUDARuntime {
     }
     if (Alignment)
       GV->setAlignment(llvm::Align(Alignment));
-    return llvm::ConstantExpr::getGetElementPtr(GV->getValueType(), GV, Zeros);
+    return GV;
   }
 
   /// Helper function that generates an empty dummy function returning void.
@@ -230,8 +226,6 @@ CGNVCUDARuntime::CGNVCUDARuntime(CodeGenModule &CGM)
   IntTy = CGM.IntTy;
   SizeTy = CGM.SizeTy;
   VoidTy = CGM.VoidTy;
-  Zeros[0] = llvm::ConstantInt::get(SizeTy, 0);
-  Zeros[1] = Zeros[0];
   PtrTy = CGM.UnqualPtrTy;
 }
 

clang/lib/CodeGen/CGObjCGNU.cpp

@@ -199,8 +199,7 @@ class CGObjCGNU : public CGObjCRuntime {
   llvm::Constant *MakeConstantString(StringRef Str, const char *Name = "") {
     ConstantAddress Array =
         CGM.GetAddrOfConstantCString(std::string(Str), Name);
-    return llvm::ConstantExpr::getGetElementPtr(Array.getElementType(),
-                                                Array.getPointer(), Zeros);
+    return Array.getPointer();
   }
 
   /// Emits a linkonce_odr string, whose name is the prefix followed by the
@@ -221,8 +220,7 @@ class CGObjCGNU : public CGObjCRuntime {
         GV->setVisibility(llvm::GlobalValue::HiddenVisibility);
       ConstStr = GV;
     }
-    return llvm::ConstantExpr::getGetElementPtr(ConstStr->getValueType(),
-                                                ConstStr, Zeros);
+    return ConstStr;
   }
 
   /// Returns a property name and encoding string.
@@ -1477,8 +1475,7 @@ class CGObjCGNUstep2 : public CGObjCGNUstep {
       GV->setVisibility(llvm::GlobalValue::HiddenVisibility);
       TypesGlobal = GV;
     }
-    return llvm::ConstantExpr::getGetElementPtr(TypesGlobal->getValueType(),
-        TypesGlobal, Zeros);
+    return TypesGlobal;
   }
   llvm::Constant *GetConstantSelector(Selector Sel,
                                       const std::string &TypeEncoding) override {

clang/lib/CodeGen/CodeGenModule.cpp

@@ -6131,9 +6131,6 @@ CodeGenModule::GetAddrOfConstantCFString(const StringLiteral *Literal) {
     return ConstantAddress(
         C, C->getValueType(), CharUnits::fromQuantity(C->getAlignment()));
 
-  llvm::Constant *Zero = llvm::Constant::getNullValue(Int32Ty);
-  llvm::Constant *Zeros[] = { Zero, Zero };
-
   const ASTContext &Context = getContext();
   const llvm::Triple &Triple = getTriple();
 
@@ -6204,8 +6201,7 @@ CodeGenModule::GetAddrOfConstantCFString(const StringLiteral *Literal) {
 
     // Decay array -> ptr
     CFConstantStringClassRef =
-        IsSwiftABI ? llvm::ConstantExpr::getPtrToInt(C, Ty)
-                   : llvm::ConstantExpr::getGetElementPtr(Ty, C, Zeros);
+        IsSwiftABI ? llvm::ConstantExpr::getPtrToInt(C, Ty) : C;
   }
 
   QualType CFTy = Context.getCFConstantStringType();
@@ -6261,10 +6257,7 @@ CodeGenModule::GetAddrOfConstantCFString(const StringLiteral *Literal) {
     GV->setSection(".rodata");
 
   // String.
-  llvm::Constant *Str =
-      llvm::ConstantExpr::getGetElementPtr(GV->getValueType(), GV, Zeros);
-
-  Fields.add(Str);
+  Fields.add(GV);
 
   // String length.
   llvm::IntegerType *LengthTy =