[AVR] Automatically link CRT and libgcc from the system avr-gcc

Summary:
This patch modifies the AVR toolchain so that if avr-gcc and avr-libc
are detected during compilation, the CRT, libgcc, libm, and libc anre
linked.

This matches avr-gcc's default behaviour, and the expected behaviour of
all C compilers - including the C runtime.

avr-gcc also needs a -mmcu specified in order to link runtime libraries.

The difference betwen this patch and avr-gcc is that this patch will
warn users whenever they compile without a runtime, as opposed to GCC,
which silently trims the runtime libs from the linker arguments when no
-mmcu is specified.

Reviewers: aaron.ballman, kparzysz, asb, hfinkel, brucehoult, TimNN

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D54334

llvm-svn: 361116

1 files changed, 9 insertions, 0 deletions

diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
index 9180afd9105..d233d443ba8 100644
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -1926,6 +1926,9 @@ void Generic_GCC::GCCInstallationDetector::AddDefaultGCCPrefixes(
   static const char *const ARMebHFTriples[] = {
       "armeb-linux-gnueabihf", "armebv7hl-redhat-linux-gnueabi"};
 
+  static const char *const AVRLibDirs[] = {"/lib"};
+  static const char *const AVRTriples[] = {"avr"};
+
   static const char *const X86_64LibDirs[] = {"/lib64", "/lib"};
   static const char *const X86_64Triples[] = {
       "x86_64-linux-gnu",       "x86_64-unknown-linux-gnu",
@@ -2146,6 +2149,10 @@ void Generic_GCC::GCCInstallationDetector::AddDefaultGCCPrefixes(
       TripleAliases.append(begin(ARMebTriples), end(ARMebTriples));
     }
     break;
+  case llvm::Triple::avr:
+    LibDirs.append(begin(AVRLibDirs), end(AVRLibDirs));
+    TripleAliases.append(begin(AVRTriples), end(AVRTriples));
+    break;
   case llvm::Triple::x86_64:
     LibDirs.append(begin(X86_64LibDirs), end(X86_64LibDirs));
     TripleAliases.append(begin(X86_64Triples), end(X86_64Triples));
@@ -2286,6 +2293,8 @@ bool Generic_GCC::GCCInstallationDetector::ScanGCCForMultilibs(
     findRISCVMultilibs(D, TargetTriple, Path, Args, Detected);
   } 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;