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[WinEH] Make llvm.eh.actions use frameescape indices for catch params

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This makes it possible to use the same representation of llvm.eh.actions
in outlined handlers as we use in the parent function because i32's are
just constants that can be copied freely between functions.

I had to add a sentinel alloca to the list of child allocas so that we
don't try to sink the catch object into the handler. Normally, one would
use nullptr for this kind of thing, but TinyPtrVector doesn't support
null elements. More than that, it's elements have to have a suitable
alignment. Therefore, I settled on this for my sentinel:

  AllocaInst *getCatchObjectSentinel() {
    return static_cast<AllocaInst *>(nullptr) + 1;
  }

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233947 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Kleckner
2015-04-02 21:13:31 +00:00
parent 5b93ab6cde
commit df4fd4fc4e
12 changed files with 84 additions and 39 deletions
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28
docs/ExceptionHandling.rst
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@@ -519,25 +519,29 @@ action.
A code of ``i32 1`` indicates a catch action, which expects three additional
arguments. Different EH schemes give different meanings to the three arguments,
but the first argument indicates whether the catch should fire, the second is a
pointer to stack object where the exception object should be stored, and the
third is the code to run to catch the exception.
but the first argument indicates whether the catch should fire, the second is
the frameescape index of the exception object, and the third is the code to run
to catch the exception.
For Windows C++ exception handling, the first argument for a catch handler is a
pointer to the RTTI type descriptor for the object to catch. The third argument
is a pointer to a function implementing the catch. This function returns the
address of the basic block where execution should resume after handling the
exception.
pointer to the RTTI type descriptor for the object to catch. The second
argument is an index into the argument list of the ``llvm.frameescape`` call in
the main function. The exception object will be copied into the provided stack
object. If the exception object is not required, this argument should be -1.
The third argument is a pointer to a function implementing the catch. This
function returns the address of the basic block where execution should resume
after handling the exception.
For Windows SEH, the first argument is a pointer to the filter function, which
indicates if the exception should be caught or not. The second argument is
typically null. The third argument is the address of a basic block where the
exception will be handled. In other words, catch handlers are not outlined in
SEH. After running cleanups, execution immediately resumes at this PC.
typically negative one. The third argument is the address of a basic block
where the exception will be handled. In other words, catch handlers are not
outlined in SEH. After running cleanups, execution immediately resumes at this
PC.
In order to preserve the structure of the CFG, a call to '``llvm.eh.actions``'
must be followed by an ':ref:`indirectbr <i_indirectbr>`' instruction that jumps
to the result of the intrinsic call.
must be followed by an ':ref:`indirectbr <i_indirectbr>`' instruction that
jumps to the result of the intrinsic call.
``llvm.eh.unwindhelp``
----------------------