[compiler-rt][RISCV] Use muldi3 builtin assembly implementation

[luismarques]

Summary

D80465 added an assembly implementation of muldi3 for RISC-V but it didn't add it to the cmake *_SOURCES list, so the C implementation was being used instead. This patch fixes that.

[lenary]

I haven't had time to try building compiler-rt with this fix, however there is nowhere else in the build system that riscv/muldi3.S is referenced, so I'm happy to accept this patch as improving compiler-rt.

[thakis]

compiler-rt/lib/builtins/CMakeLists.txt

574

Is it intentional that mulsi3.S is up here but muldi3.S is in a separate 64-bit block below?

[luismarques]

compiler-rt/lib/builtins/CMakeLists.txt

574

Yes. for riscv32 we use the generic muldi3 (which will internally rely on mulsi3), while for riscv64 we only need muldi3, so I think they never need to be included at the same time, and thus they appear in these separate blocks. (Please let me know if you/anyone thinks I'm wrong about this.)

[lenary]

@thakis this also matches the #ifdefs in the files themselves.

[luismarques]

In D86036#2233630, @lenary wrote:

@thakis this also matches the #ifdefs in the files themselves.

Hopefully not for long: D86457 :-)

[lenary]

In D86036#2233640, @luismarques wrote:

In D86036#2233630, @lenary wrote:

@thakis this also matches the #ifdefs in the files themselves.

Hopefully not for long: D86457 :-)

I meant muldi3.S and mulsi3.S, not the .inc file - I don't think either is changed by that patch yet?

[luismarques]

In D86036#2233649, @lenary wrote:

I meant muldi3.S and mulsi3.S, not the .inc file - I don't think either is changed by that patch yet?

Yes, those #ifs remain. Honestly I don't see much point in them though, the way they are currently written. Including riscv\mulsi3.S in the CMake config should already imply the correct thing (otherwise it's super misleading at best), so the #if shouldn't really be required. Perhaps they would make more sense in terms of a #if !... #error ... #endif flow to guard against unexpected conditions.

compiler-rt/lib/builtins/CMakeLists.txt

set(powerpc64_SOURCES
   ppc/gcc_qsub.c
   ppc/multc3.c
   ${GENERIC_SOURCES}
 )
 set(powerpc64le_SOURCES ${powerpc64_SOURCES})
 
 set(riscv_SOURCES ${GENERIC_SOURCES} ${GENERIC_TF_SOURCES})
 set(riscv32_SOURCES
   riscv/mulsi3.S
   ${riscv_SOURCES}
 )
-set(riscv64_SOURCES ${riscv_SOURCES})
+set(riscv64_SOURCES
+  riscv/muldi3.S
+  ${riscv_SOURCES}
+)
 
 set(sparc_SOURCES ${GENERIC_SOURCES} ${GENERIC_TF_SOURCES})
 set(sparcv9_SOURCES ${GENERIC_SOURCES} ${GENERIC_TF_SOURCES})
 
 set(wasm32_SOURCES
   ${GENERIC_TF_SOURCES}
   ${GENERIC_SOURCES}
 )