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What is it?

This is a fork of the GCC project https://gcc.gnu.org with additional changes to the releases/gcc-8 branch.

All the changes you find in this fork address the AVR backend.

Why is it here?

The latest of the GCC v8 releases, v8.5, was created from releases/gcc-8 in May 2021, and then that branch was closed.

Some patches are back-ported from v14 to v8 because newer versions of GCC may have some problems that v8 does not have. However, v8 has also some problems and shortcoming, which this fork tries to address.

Bugs Fixed

  • PR92606: Inter-procedural analysis optimizes data across address-spaces and PROGMEM. This is fixed in v14 for address-spaces but still persists for PROGMEM. The local fix just disables the bogus IPA optimization.

  • PR101188: A rare wrong-code bug that can be tracket back to GCC v5 and beyond. It's fixed in v14 but not in v13.2, and it is unclear if the fix will be back-ported to the v13 branch.

  • PR107201: The -nodevicelib option did not work as expected for devices which start with "AVR", like AVR32DA32.

  • The options -g -mrelax -flto did not work together and failed with an --relax and -r may not be used together error from the linker.

  • PR88236, PR87376, PR115726: Fixed code for reading from address-space __memx (fixed in v12.5, v13.4 and v14.2+).

  • PR98762: Fixed a wrong code bug on Reduced Tiny (fixed in v12.5, v13.4 and v14.2+).

  • PR116407: Fixed a "relocation truncated to fit" error from the linker (fixed in v13.4, and v14.3+).

Extensions

  • Support all devices that avr-gcc v14 supports. For a complete list, see the online documentation on ‑mmcu=.

  • PR112944: Support command-line option -m[no-]rodata-in-ram. When Binutils support PR31124, then read-only data on AVR64* and AVR128* devices is located in program memory. For a detailed description with further reading, see the GCC v14 Release Notes.

  • PR116056: Support function attribues signal(n), interrupt(n) and noblock, see also the GCC v15 Release Notes.

  • Support built-in function __builtin_avr_mask1, see the GCC v15 Release Notes.

  • In C++ compilations, don't implicitly wrap headers found per -isystem in extern "C" { ... }.

Problems Avoided

The GCC v8 release avoids some problems of more recent compiler versions, namely the following performance regressions from the register allocator:

  • PR110093: Move frenzy leading to code bloat.

  • PR114243: -fsplit-wide-types bloats float code by more than 50%. As a work-around, -fno-split-wide-types can be used, though that option cannot be recommended in general.

  • PR90706: Useless code generated for stack / register operations (partially fixed in v12.3+).