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[Coroutines] Reuse storage for local variables with non-overlapping lifetimes

Authored by ChuanqiXu on Sep 28 2020, 12:40 AM.

Description

[Coroutines] Reuse storage for local variables with non-overlapping lifetimes

bug 45566 shows the process of building coroutine frame won't consider
that the lifetimes of different local variables are not overlapped,
which means the compiler could generates smaller frame.

This patch calculate the lifetime range of each alloca by StackLifetime
class. Then the patch build non-overlapped sets for allocas whose
lifetime ranges are not overlapped. We use the largest type in a
non-overlapped set as the field type in the frame. In insertSpills
process, if we find the type of field is not the same with the alloca,
we cast the pointer to the field type to the pointer to the alloca type.
Since the lifetime range of alloca in one non-overlapped set is not
overlapped with each other, it should be ok to reuse the storage space
in the frame.

Test plan: check-llvm, check-clang, cppcoro, folly

Reviewers: junparser, lxfind, modocache

Differential Revision: https://reviews.llvm.org/D87596