tree 38ccf519ef4bd4d2d26d9ed68de0af621007bb3d
parent 24878cf6b025a1db14feee2d9197b129a504e041
author Fangrui Song <i@maskray.me> 1611271162 -0800
committer Copybara-Service <copybara-worker@google.com> 1611278705 -0800

[libc++abi] Simplify scan_eh_tab

1.
All `_URC_HANDLER_FOUND` return values need to set `landingPad`
and its value does not matter for `_URC_CONTINUE_UNWIND`. So we
can always set `landingPad` to unify code.

2.
For an exception specification (`ttypeIndex < 0`), we can check `_UA_FORCE_UNWIND` first.

3.
The so-called type 3 search (`actions & _UA_CLEANUP_PHASE && !(actions & _UA_HANDLER_FRAME)`)
is actually conceptually wrong.  For a catch handler or an unmatched dynamic
exception specification, `_UA_HANDLER_FOUND` should be returned immediately.  It
still appeared to work because the `ttypeIndex==0` case would return
`_UA_HANDLER_FOUND` at a later time.

This patch fixes the conceptual error and simplifies the code by handling type 3
the same way as type 2 (which is also what libsupc++ does).
The only difference between phase 1 and phase 2 is what to do with a cleanup
(`actionEntry==0`, or a `ttypeIndex==0` is found in the action record chain):
phase 1 returns `_URC_CONTINUE_UNWIND` while phase 2 returns `_URC_HANDLER_FOUND`.

Reviewed By: #libc_abi, compnerd

Differential Revision: https://reviews.llvm.org/D93190

GitOrigin-RevId: cfe9ccbddd98b55e49e46bb40877ece6a47a7625