From 3778f21b17e675c2fd1600901361fa4a73888eba Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Sun, 16 Aug 2009 21:26:11 +0000 Subject: [PATCH] Add a getOffsetOf, for building a target-independent expression for offsetof, similar to getSizeOf for sizeof. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79208 91177308-0d34-0410-b5e6-96231b3b80d8 --- include/llvm/Constants.h | 5 +++++ lib/VMCore/Constants.cpp | 12 ++++++++++++ 2 files changed, 17 insertions(+) diff --git a/include/llvm/Constants.h b/include/llvm/Constants.h index e26bb62c357..a66773c0b53 100644 --- a/include/llvm/Constants.h +++ b/include/llvm/Constants.h @@ -602,6 +602,11 @@ public: /// independent way (Note: the return type is an i64). /// static Constant* getSizeOf(const Type* Ty); + + /// getOffsetOf constant expr - computes the offset of a field in a target + /// independent way (Note: the return type is an i64). + /// + static Constant* getOffsetOf(const StructType* Ty, unsigned FieldNo); static Constant* getNeg(Constant* C); static Constant* getFNeg(Constant* C); diff --git a/lib/VMCore/Constants.cpp b/lib/VMCore/Constants.cpp index 647bc1225a2..f820033932d 100644 --- a/lib/VMCore/Constants.cpp +++ b/lib/VMCore/Constants.cpp @@ -1391,6 +1391,18 @@ Constant* ConstantExpr::getAlignOf(const Type* Ty) { Type::getInt32Ty(Ty->getContext())); } +Constant* ConstantExpr::getOffsetOf(const StructType* STy, unsigned FieldNo) { + // offsetof is implemented as: (i64) gep (Ty*)null, 0, FieldNo + // Note that a non-inbounds gep is used, as null isn't within any object. + Constant *GEPIdx[] = { + ConstantInt::get(Type::getInt64Ty(STy->getContext()), 0), + ConstantInt::get(Type::getInt32Ty(STy->getContext()), FieldNo) + }; + Constant *GEP = getGetElementPtr( + Constant::getNullValue(PointerType::getUnqual(STy)), GEPIdx, 2); + return getCast(Instruction::PtrToInt, GEP, + Type::getInt64Ty(STy->getContext())); +} Constant *ConstantExpr::getCompare(unsigned short pred, Constant *C1, Constant *C2) { -- 2.34.1