89f36dd8f3
As stated in https://discourse.llvm.org/t/rfc-llc-add-expandlargeintfpconvert-pass-for-fp-int-conversion-of-large-bitint/65528, this implementation is very similar to ExpandLargeDivRem, which expands ‘fptoui .. to’, ‘fptosi .. to’, ‘uitofp .. to’, ‘sitofp .. to’ instructions with a bitwidth above a threshold into auto-generated functions. This is useful for targets like x86_64 that cannot lower fp convertions with more than 128 bits. The expanded nodes are referring from the IR generated by `compiler-rt/lib/builtins/floattidf.c`, `compiler-rt/lib/builtins/fixdfti.c`, and etc. Corner cases: 1. For fp16: as there is no related builtins added in compliler-rt. So I mainly utilized the fp32 <-> fp16 lib calls to implement. 2. For fp80: as this pass is soft fp emulation and no fp80 instructions can help in this problem. I recommend users to deprecate this usage. For now, the implementation uses fp128 as the temporary conversion type and inserts fptrunc/ext at top/end of the function. 3. For bf16: as clang FE currently doesn't support bf16 algorithm operations (convert to int, float, +, -, *, ...), this patch doesn't consider bf16 for now. 4. For unsigned FPToI: since both default hardware behaviors and libgcc are ignoring "returns 0 for negative input" spec. This pass follows this old way to ignore unsigned FPToI. See this example: https://gcc.godbolt.org/z/bnv3jqW1M The end-to-end tests are uploaded at https://reviews.llvm.org/D138261 Reviewed By: LuoYuanke, mgehre-amd Differential Revision: https://reviews.llvm.org/D137241 |
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README.txt
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