本文整理汇总了C++中AliasAnalysis::isMustAlias方法的典型用法代码示例。如果您正苦于以下问题：C++ AliasAnalysis::isMustAlias方法的具体用法？C++ AliasAnalysis::isMustAlias怎么用？C++ AliasAnalysis::isMustAlias使用的例子？那么, 这里精选的方法代码示例或许可以为您提供帮助。您也可以进一步了解该方法所在类AliasAnalysis的用法示例。
在下文中一共展示了AliasAnalysis::isMustAlias方法的1个代码示例，这些例子默认根据受欢迎程度排序。您可以为喜欢或者感觉有用的代码点赞，您的评价将有助于系统推荐出更棒的C++代码示例。
示例1: isPossibleSelfRead
/// isPossibleSelfRead - If 'Inst' might be a self read (i.e. a noop copy of a
/// memory region into an identical pointer) then it doesn't actually make its
/// input dead in the traditional sense. Consider this case:
///
/// memcpy(A <- B)
/// memcpy(A <- A)
///
/// In this case, the second store to A does not make the first store to A dead.
/// The usual situation isn't an explicit A<-A store like this (which can be
/// trivially removed) but a case where two pointers may alias.
///
/// This function detects when it is unsafe to remove a dependent instruction
/// because the DSE inducing instruction may be a self-read.
static bool isPossibleSelfRead(Instruction *Inst,
const AliasAnalysis::Location &InstStoreLoc,
Instruction *DepWrite, AliasAnalysis &AA) {
// Self reads can only happen for instructions that read memory. Get the
// location read.
AliasAnalysis::Location InstReadLoc = getLocForRead(Inst, AA);
if (!InstReadLoc.Ptr) return false; // Not a reading instruction.
// If the read and written loc obviously don't alias, it isn't a read.
if (AA.isNoAlias(InstReadLoc, InstStoreLoc)) return false;
// Okay, 'Inst' may copy over itself. However, we can still remove a the
// DepWrite instruction if we can prove that it reads from the same location
// as Inst. This handles useful cases like:
// memcpy(A <- B)
// memcpy(A <- B)
// Here we don't know if A/B may alias, but we do know that B/B are must
// aliases, so removing the first memcpy is safe (assuming it writes <= #
// bytes as the second one.
AliasAnalysis::Location DepReadLoc = getLocForRead(DepWrite, AA);
if (DepReadLoc.Ptr && AA.isMustAlias(InstReadLoc.Ptr, DepReadLoc.Ptr))
return false;
// If DepWrite doesn't read memory or if we can't prove it is a must alias,
// then it can't be considered dead.
return true;
}