[AVR][clang] Pass '-fno-use-init-array' to cc1 as default

On AVR, '.ctors' is used, not '.init_array'. Make this the default
unless specifically overridden by driver argument.

This matches gcc, and it matches the behavior in (e.g.) the NetBSD
driver (for certain OS variants).

Reviewed by: MaskRay

Differential Revision: https://reviews.llvm.org/D107610

clang/lib/Driver/ToolChains/AVR.cpp

@@ -370,6 +370,16 @@ void AVRToolChain::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
     addSystemInclude(DriverArgs, CC1Args, AVRInc);
 }
 
+void AVRToolChain::addClangTargetOptions(
+    const llvm::opt::ArgList &DriverArgs, llvm::opt::ArgStringList &CC1Args,
+    Action::OffloadKind DeviceOffloadKind) const {
+  // By default, use `.ctors` (not `.init_array`), as required by libgcc, which
+  // runs constructors/destructors on AVR.
+  if (!DriverArgs.hasFlag(options::OPT_fuse_init_array,
+                          options::OPT_fno_use_init_array, false))
+    CC1Args.push_back("-fno-use-init-array");
+}
+
 Tool *AVRToolChain::buildLinker() const {
   return new tools::AVR::Linker(getTriple(), *this, LinkStdlib);
 }

clang/lib/Driver/ToolChains/AVR.h

@@ -11,8 +11,8 @@
 
 #include "Gnu.h"
 #include "clang/Driver/InputInfo.h"
-#include "clang/Driver/ToolChain.h"
 #include "clang/Driver/Tool.h"
+#include "clang/Driver/ToolChain.h"
 
 namespace clang {
 namespace driver {
@@ -26,6 +26,11 @@ public:
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
 
+  void
+  addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
+                        llvm::opt::ArgStringList &CC1Args,
+                        Action::OffloadKind DeviceOffloadKind) const override;
+
 protected:
   Tool *buildLinker() const override;
 

clang/test/Driver/avr-toolchain.c

@@ -1,7 +1,7 @@
 // A basic clang -cc1 command-line.
 
 // RUN: %clang %s -### -no-canonical-prefixes -target avr 2>&1 | FileCheck -check-prefix=CC1 %s
-// CC1: clang{{.*}} "-cc1" "-triple" "avr"
+// CC1: clang{{.*}} "-cc1" "-triple" "avr" {{.*}} "-fno-use-init-array"
 
 // RUN: %clang %s -### -no-canonical-prefixes -target avr --sysroot %S/Inputs/basic_avr_tree 2>&1 | FileCheck -check-prefix CC1A %s
 // CC1A: clang{{.*}} "-cc1" "-triple" "avr" {{.*}} "-internal-isystem" {{".*avr/include"}}