On 2020-11-21 12:27, J.W. Jagersma wrote:
> ...
> Another idea I had is to introduce a new operand modifier, eg. '-', which
> would signify that the output *must* be considered clobbered on exception,
> and it would be an error if a copy is not possible. Then the meaning of '+'
> can be extended to say that the output must be valid regardless of whether an
> exception occured or not. Modifier '=' would mean the same as '+' with the
> additional implication that it is okay to eliminate earlier assignments, so
> that its value on the EH edge would be undefined.
I've been working on implementing this, but I ran into an issue:
First of all, in the first version of this patch I had to make sure that
debug stmts were inserted across the fallthrough edge, so that they don't
appear at the end a basic block. I was surprised to find that this is no
longer necessary.
Next I discovered that the following test case fails (returns -1):
int f ()
{
int i = 0;
try { asm ("mov %0, 1; ud2" : "+r" (i)); }
catch (...) { }
return i - 1;
}
And this does succeed with a memory operand.
It seems that something changed in the past few months, and now asm register
outputs are already being assigned via a temporary variable, somewhere. Does
anyone know where that might be?
