Saturday, April 21, 2012

Lucien on AtariAge has found a lot of problems in the compiler. Time to get back into bugfix mode.

First off there's a problem with stack construction. Apparently I was double counting the saved register space in the stack frame. The local variables are allocated from the start of the frame. I was confused and thought that the frame was required to be at the bottom of the stack, and so I made space for the saved registers, which are stored below the local variables.

This caused all frame local variables to be misaddressed, corrupting some saved registers. Lucien provided a fix, which was mostly right, but miscalculated the number of saved registers in some optimization modes. I think that's the last time the stack code needs to be changed.

There was another problem in the assembler, I thought i was being clever in allowing either TI-style single quotes or C-style double quotes for string constants. That code worked fine for C-style strings, but always closed the string when TI-style strings were used. This is a problem since GCC was configured to always use TI-style strings for the emitted assembly. This means there was no way to use single quotes in compiled code.

This was fixed by rewriting a good chunk of the string handling code in GAS. Now if a TI-style quote is used ('like this'), no escape sequences will be recognized except for the sequence '' which is converted to one single quote character. If C-style quotes are used ("like this"), all standard escape sequences are recognized. This allows assembly authors to chose the style they prefer while remaining compatible with the TI conventions. GCC always uses TI-style strings, so users will see their expected output.

I think there's another five or so GCC bugs in Lucien's latest game. I'll start going through it and see what I can do.

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