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Introduce a typing refinenement on tagged data

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using the 'volatile' qualifier. This should not have any operational consequences
on code, because tags should always be stripped off (giving a non-volatile pointer)
before dereferencing. The new qualification is there to catch some attempts to use
tagged pointers in a context where an untagged pointer is appropriate.

Notably this approach does not catch dereferencing of tagged pointers, but helps
in separating the two concepts a bit.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57641 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Gabor Greif 2008-10-16 15:33:02 +00:00
parent cc30d9caa5
commit 023f84ecaf
2 changed files with 8 additions and 10 deletions
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10
include/llvm/Use.h
View File

@ -34,27 +34,27 @@ enum Tag { noTag, tagOne, tagTwo, tagThree };
/// addTag - insert tag bits into an (untagged) pointer
template <typename T, typename TAG>
inline T *addTag(const T *P, TAG Tag) {
inline volatile T *addTag(const T *P, TAG Tag) {
return reinterpret_cast<T*>(ptrdiff_t(P) | Tag);
}
/// stripTag - remove tag bits from a pointer,
/// making it dereferencable
template <ptrdiff_t MASK, typename T>
inline T *stripTag(const T *P) {
inline T *stripTag(const volatile T *P) {
return reinterpret_cast<T*>(ptrdiff_t(P) & ~MASK);
}
/// extractTag - extract tag bits from a pointer
template <typename TAG, TAG MASK, typename T>
inline TAG extractTag(const T *P) {
inline TAG extractTag(const volatile T *P) {
return TAG(ptrdiff_t(P) & MASK);
}
/// transferTag - transfer tag bits from a pointer,
/// to an untagged pointer
template <ptrdiff_t MASK, typename T>
inline T *transferTag(const T *From, const T *To) {
inline volatile T *transferTag(const volatile T *From, const T *To) {
return reinterpret_cast<T*>((ptrdiff_t(From) & MASK) | ptrdiff_t(To));
}
@ -126,7 +126,7 @@ private:
static Use *initTags(Use *Start, Use *Stop, ptrdiff_t Done = 0);
Value *Val;
Use *Next, **Prev;
Use *Next, *volatile*Prev;
void setPrev(Use **NewPrev) {
Prev = transferTag<fullStopTag>(Prev, NewPrev);

8
lib/VMCore/Use.cpp
View File

@ -127,7 +127,7 @@ void Use::zap(Use *Start, const Use *Stop, bool del) {
//===----------------------------------------------------------------------===//
struct AugmentedUse : Use {
User *ref;
volatile User *ref;
AugmentedUse(); // not implemented
};
@ -138,12 +138,10 @@ struct AugmentedUse : Use {
User *Use::getUser() const {
const Use *End = getImpliedUser();
User *She = static_cast<const AugmentedUse*>(End - 1)->ref;
She = extractTag<Tag, tagOne>(She)
volatile User *She = static_cast<const AugmentedUse*>(End - 1)->ref;
return extractTag<Tag, tagOne>(She)
? llvm::stripTag<tagOne>(She)
: reinterpret_cast<User*>(const_cast<Use*>(End));
return She;
}
//===----------------------------------------------------------------------===//