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avr-llvm / llvm

[MERGED UPSTREAM] AVR backend for the LLVM compiler library
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Are we coverered for issues with SBR? #58

Closed RandomInsano closed 9 years ago

RandomInsano commented 9 years ago

SBR can only operate on registers R16 to R31, if anything is lowered to use the first sixteen registers they're going to be in trouble since the results will be stored in the wrong location.

I need to find out how to do negative tests in the instruction testing framework.

RandomInsano commented 9 years ago

I'm guessing "let Constraints" should include something to handle this. If no one is sure, I'll post to the LLVM mailing list.

RandomInsano commented 9 years ago

It looks like we do fail properly. I just need to learn how to add the proper unit test.

dylanmckay commented 9 years ago

If you look at test/CodeGen/Mips/inlineasm-cnstrnt-bad-I-1.ll, you can see how negative tests are implemented:

By prefixing the RUN comment with not:

; RUN: not llc -march=mipsel < %s  2> %t
dylanmckay commented 9 years ago

I believe we do handle this properly: llvm-mc will fail with sbr r3, 5 with "invalid operand" and sbr r17, 5 succeeds.

We could open an issue to improve error messages where only a subset of a register class is expected.

RandomInsano commented 9 years ago

Honestly, that's probably a good idea. I'll go digging when I've got some time.

dylanmckay commented 9 years ago

I decided to open up a new issue instead - see #67.