[RISCV]: Adjust riscv64 GCC detector to also check for existence of crtbegin.o in the default multilib dir, like most other ports.

[MaskRay]

Summary

Adjust riscv64 GCC detector to also check for existence of
crtbegin.o in the default multilib dir, like most other ports.
Fixes FTBFS on riscv64, since on Ubuntu /usr/lib/gcc/riscv64-linux-gnu/10
exists but is empty (gcc-10-base is installed, but libgcc-10-dev is not).

This fixes build failures on debian/ubuntu riscv64 when the gcc-10 is only minimally installed.

[luismarques]

I think this makes sense and is correctly implemented but I would like other people to look at this.
It would also benefit from adding tests, rejecting the "minimally installed" scenario and accepting the proper install.

[LocutusOfBorg]

In D78021#1978663, @luismarques wrote:

I think this makes sense and is correctly implemented but I would like other people to look at this.
It would also benefit from adding tests, rejecting the "minimally installed" scenario and accepting the proper install.

I don't think we should deal with that scenario, because the "minimally installed" gcc scenario works flawlessly, it happens IIRC when e.g. gcc defaults to VERSION+1 but libgcc is still at the old version.
But in any case, nothing we should worry about, it should work and build correctly in any case!

[khchen]

Could you add a testcase? It will helpful to see what issue fixed in this patch. thanks.

[LocutusOfBorg]

Hello, sorry but I don't really understand how to add a testcase...

[eopXD]

Hello, sorry but I don't really understand how to add a testcase...

LLVM_DEBUG() and llvm::dbgs() under llvm/Support/Debug.h can help you emit any debug log. Under a test case you can use ; REQUIRES: asserts to catch these debug logs under Debug mode. Hope this can help you on this.

[LocutusOfBorg]

this is not needed anymore, we can close it.

[MaskRay]

I wish that we have more descriptions of the environment and how this works, but I'll close this as instructed for now.
These subtle changes need testing.

clang/lib/Driver/ToolChains/Gnu.cpp

if (!Added_ABIs.count(Element.mabi)) {
                       Twine("mabi=", Element.mabi).str().c_str(), Flags);
     }
   }
 
   if (RISCVMultilibs.select(Flags, Result.SelectedMultilib))
     Result.Multilibs = RISCVMultilibs;
 }
 
-static void findRISCVMultilibs(const Driver &D,
+static bool findRISCVMultilibs(const Driver &D,
                                const llvm::Triple &TargetTriple, StringRef Path,
                                const ArgList &Args, DetectedMultilibs &Result) {
-  if (TargetTriple.getOS() == llvm::Triple::UnknownOS)
-    return findRISCVBareMetalMultilibs(D, TargetTriple, Path, Args, Result);
+  if (TargetTriple.getOS() == llvm::Triple::UnknownOS) {
+    findRISCVBareMetalMultilibs(D, TargetTriple, Path, Args, Result);
+    return true;
+  }
 
   FilterNonExistent NonExistent(Path, "/crtbegin.o", D.getVFS());
+  Multilib Default;
   Multilib Ilp32 = makeMultilib("lib32/ilp32").flag("+m32").flag("+mabi=ilp32");
   Multilib Ilp32f =
       makeMultilib("lib32/ilp32f").flag("+m32").flag("+mabi=ilp32f");
   Multilib Ilp32d =
       makeMultilib("lib32/ilp32d").flag("+m32").flag("+mabi=ilp32d");
   Multilib Lp64 = makeMultilib("lib64/lp64").flag("+m64").flag("+mabi=lp64");
   Multilib Lp64f = makeMultilib("lib64/lp64f").flag("+m64").flag("+mabi=lp64f");
   Multilib Lp64d = makeMultilib("lib64/lp64d").flag("+m64").flag("+mabi=lp64d");
   MultilibSet RISCVMultilibs =
       MultilibSet()
-          .Either({Ilp32, Ilp32f, Ilp32d, Lp64, Lp64f, Lp64d})
+          .Either({Default, Ilp32, Ilp32f, Ilp32d, Lp64, Lp64f, Lp64d})
           .FilterOut(NonExistent);
 
   Multilib::flags_list Flags;
   bool IsRV64 = TargetTriple.getArch() == llvm::Triple::riscv64;
   StringRef ABIName = tools::riscv::getRISCVABI(Args, TargetTriple);
 
   addMultilibFlag(!IsRV64, "m32", Flags);
   addMultilibFlag(IsRV64, "m64", Flags);
   addMultilibFlag(ABIName == "ilp32", "mabi=ilp32", Flags);
   addMultilibFlag(ABIName == "ilp32f", "mabi=ilp32f", Flags);
   addMultilibFlag(ABIName == "ilp32d", "mabi=ilp32d", Flags);
   addMultilibFlag(ABIName == "lp64", "mabi=lp64", Flags);
   addMultilibFlag(ABIName == "lp64f", "mabi=lp64f", Flags);
   addMultilibFlag(ABIName == "lp64d", "mabi=lp64d", Flags);
 
-  if (RISCVMultilibs.select(Flags, Result.SelectedMultilib))
-    Result.Multilibs = RISCVMultilibs;
+  if (!RISCVMultilibs.select(Flags, Result.SelectedMultilib))
+    return false;
+
+  return true;
 }
 
 static bool findBiarchMultilibs(const Driver &D,
                                 const llvm::Triple &TargetTriple,
                                 StringRef Path, const ArgList &Args,
                                 bool NeedsBiarchSuffix,
                                 DetectedMultilibs &Result) {
   Multilib Default;
bool Generic_GCC::GCCInstallationDetector::ScanGCCForMultilibs(
   // so handle them there
   if (isArmOrThumbArch(TargetArch) && TargetTriple.isAndroid()) {
     // It should also work without multilibs in a simplified toolchain.
     findAndroidArmMultilibs(D, TargetTriple, Path, Args, Detected);
   } else if (TargetTriple.isMIPS()) {
     if (!findMIPSMultilibs(D, TargetTriple, Path, Args, Detected))
       return false;
   } else if (TargetTriple.isRISCV()) {
-    findRISCVMultilibs(D, TargetTriple, Path, Args, Detected);
+    if (!findRISCVMultilibs(D, TargetTriple, Path, Args, Detected))
+      return false;
   } else if (isMSP430(TargetArch)) {
     findMSP430Multilibs(D, TargetTriple, Path, Args, Detected);
   } else if (TargetArch == llvm::Triple::avr) {
     // AVR has no multilibs.
   } else if (!findBiarchMultilibs(D, TargetTriple, Path, Args,
                                   NeedsBiarchSuffix, Detected)) {
     return false;
   }