[PATCH] D136169: [AMDGPU] Avoid SCC clobbering before S_CSELECT_B32

[Sebastian Neubauer via Phabricator via llvm-commits]

sebastian-ne added inline comments.


================
Comment at: llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp:2238
+              .addReg(FrameReg)
+              .addImm(Offset);
+          BuildMI(*MBB, MI, DL, TII->get(AMDGPU::S_BITCMP1_B32))
----------------
alex-t wrote:
> sebastian-ne wrote:
> > Maybe it makes sense to add an assert, that the least significant bit of `Offset` is indeed 0? (here and for s_subb below)
> As far as I know, the flat scratch offset is always dword-aligned. If it is not we've got the UB anyway. So, the assert does not help.
Sure, an assert doesn’t help correctness. But if at some point in the future, we encounter a case where the offset is not aligned – maybe due to a bug elsewhere – having an assert makes it easy to find why some memory got corrupted.
Without an assert, it will surely take hours to find out what is going on.


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  https://reviews.llvm.org/D136169/new/

https://reviews.llvm.org/D136169