A jit::BaselineFrame is followed in memory by a jit::JitFrameLayout; as the
stack grows downwards, the JitFrameLayout is pushed first, "followed" by the
BaselineFrame at lower addresses, and finally by locals and the operand stack.
A BaselineFrame* points, naturally, at the BaselineFrame structure, but we use
the address of the JitFrameLayout as the address for a physical Ion frame -
actually, a pointer to its base class, jit::CommonFrameLayout. This means that,
if OSR replaces a BaselineFrame with an Ion frame, then walking the stack with a
FrameIter will see an Ion frame where a BaselineFrame used to appear, and the
LiveSavedFrameCache::FramePtr we'll construct from that FrameIter will be
different.
If the LiveSavedFrameCache wants to assert that frames with their bits set
indeed appear in the cache, then we'd better clear the flag whenever we OSR the
frame. But this is a pity; it's still the same frame, representing the same
function activation.
Meanwhile, both BaselineFrame and CommonFrameLayout have their own
hasCachedSavedFrame flags, which is confusing.
This patch changes FramePtr to use a jit::CommonFrameLayout* for both Baseline
frames and physical Ion frames, so OSR does not change the frame's address, and
use CommonFrameLayout's hasCachedSavedFrame flag for both types, so that OSR
need not take any explicit steps to propagate the cached flag to the new frame.
MozReview-Commit-ID: rOMjUXlwIQ
--HG--
extra : rebase_source : 360cca36216e24b5668c28e7f4d02ef76b6a0fb8
extra : source : 000d13ca4b5c8427308753a4a1e23f56245dc19f
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00f3f3318d