SjoerdMeijer added inline comments.
================ Comment at: clang/test/CodeGen/arm-bf16-params-returns.c:5 +// RUN: %clang_cc1 -triple aarch64-arm-none-eabi -target-abi aapcs -mfloat-abi softfp -target-feature +bf16 -target-feature +neon -emit-llvm -O2 -o - %s | opt -S -mem2reg -sroa | FileCheck %s --check-prefix=CHECK64-SOFTFP + +// function return types ---------------- stuij wrote: > SjoerdMeijer wrote: > > what happens with `-mfloat-abi=soft`. Does that deserve a test? > Yes, this one is interesting. I think we shouldn't support bfloat at all in > combination with -mfloat-abi=soft. We don't support software emulation of > bfloat instructions and all operations on bfloat are simd instructions. > > It turns out cc1 will accept -mfloat-abi=soft with neon intrinsics, which > will happily churn out neon instructions. This doesn't sound very soft. The > driver will ignore -mfloat-abi=soft in certain combinations of cmdline > instructions, but I haven't delved deep enough to know what's what. > > GCC doesn't allow soft+neon combination. Unfortunately it will actually crash > for just a bfloat type by itself, which is quite useless without intrinsics. > The Arm GCC folks will raise a ticket on this with as proposed solution to > not allow this combination. > > As this issue seems bigger than just bfloat, and potentially there's driver > code involved as well I thought it'd make sense to handle this in a separate > patch. I think we first need agreement what -mfloat-abi=soft with bf16 means and how it should behave, document this, and have some tests. Possibly document how we diverge from this. I think I tend to disagree with this: > I think we shouldn't support bfloat at all in combination with > -mfloat-abi=soft. why would it not be supported in some way (promotions to another type, or even library calls), like the other float-types? > It turns out cc1 will accept -mfloat-abi=soft with neon intrinsics, which > will happily churn out neon instructions. I would say the fact that there are other problems, shouldn't distract us too much from trying to get this right; I think at this point that is not yet a justification. > As this issue seems bigger than just bfloat, and potentially there's driver > code involved as well I thought it'd make sense to handle this in a separate > patch. I think at this point I disagree with this, mainly because of my first point: the behaviour should be specified. I would also say that not doing this, could be a bit of bad precedent for adding a new C type. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D76077/new/ https://reviews.llvm.org/D76077 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
