[PATCH] D68407: [WIP][RISCV] Use compiler-rt if no GCC installation detected

[Edward Jones via Phabricator via cfe-commits]

edward-jones added a comment.

In D68407#1732685 <https://reviews.llvm.org/D68407#1732685>, @lenary wrote:

> This patch is looking much better, thanks for updating it.
>
> Please may you clarify what RISC-V gcc does for `-lgcc`, `-lgcc_s`, `-lgcc_eh`? Is it different to what gcc does on other targets? Being closer to matching the linker arguments that gcc provides to ld seems like a good idea, IMO.


The default behaviour on RISC-V GCC is just `-lgcc`, however for Clang if I call `tools::AddRunTimeLibs` then by default I get `-lgcc --as-needed -lgcc_s --no-as-needed` in the link step.

When libgcc is needed `tools::AddRunTimeLibs` unconditionally calls `AddUnwindLibrary`, which in turn calls `ToolChain::GetUnwindLibType` which always returns `ToolChain::UNW_Libgcc` for libgcc. The code in `AddUnwindLibrary` will then always add either `-lgcc_eh` (for a static libgcc), or `-lgcc_s` (for a shared libgcc) to the command line. I can override this by reimplementing `ToolChain::GetUnwindLibType` in the target and making it return `ToolChain::UNW_None`, but I'm not sure whether that's the desired behavior.


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