Debugging data on Alpha

[Richard Kenner]

    My guess is that the scheduler messes up the BLOCK_BEG/BLOCK_END notes.
    I've seen that happen a few times; if a BLOCK_END note is found inside
    a basic block, it'll move upward to the start of the block.

This could certainly cause problems with optimized code, but I've seen this
mostly with -O0 code.

Here's an example: look at the variables declared around line 6819
of expr.c (right before the call to get_inner_reference).  When I'm inside
that block, I'm never able to display the value of any of those variables:
it always says no such variable exists.