RuntimeLibcalls: Use array initializers for default values (#143082)

Author: arsenm

llvm/include/llvm/IR/RuntimeLibcalls.h

@@ -103,10 +103,13 @@ struct RuntimeLibcallsInfo {
 
 private:
   /// Stores the name each libcall.
-  const char *LibcallRoutineNames[RTLIB::UNKNOWN_LIBCALL + 1];
+  const char *LibcallRoutineNames[RTLIB::UNKNOWN_LIBCALL + 1] = {nullptr};
+
+  static_assert(static_cast<int>(CallingConv::C) == 0,
+                "default calling conv should be encoded as 0");
 
   /// Stores the CallingConv that should be used for each libcall.
-  CallingConv::ID LibcallCallingConvs[RTLIB::UNKNOWN_LIBCALL];
+  CallingConv::ID LibcallCallingConvs[RTLIB::UNKNOWN_LIBCALL] = {};
 
   /// The condition type that should be used to test the result of each of the
   /// soft floating-point comparison libcall against integer zero.

llvm/lib/IR/RuntimeLibcalls.cpp

@@ -284,8 +284,7 @@ void RuntimeLibcallsInfo::initSoftFloatCmpLibcallPredicates() {
 /// Set default libcall names. If a target wants to opt-out of a libcall it
 /// should be placed here.
 void RuntimeLibcallsInfo::initLibcalls(const Triple &TT) {
-  std::fill(std::begin(LibcallRoutineNames), std::end(LibcallRoutineNames),
-            nullptr);
+  initSoftFloatCmpLibcallPredicates();
 
   initSoftFloatCmpLibcallPredicates();
 
@@ -295,10 +294,6 @@ void RuntimeLibcallsInfo::initLibcalls(const Triple &TT) {
 #undef HANDLE_LIBCALL
 #undef LIBCALL_NO_NAME
 
-  // Initialize calling conventions to their default.
-  for (int LC = 0; LC < RTLIB::UNKNOWN_LIBCALL; ++LC)
-    setLibcallCallingConv((RTLIB::Libcall)LC, CallingConv::C);
-
   // Use the f128 variants of math functions on x86
   if (TT.isX86() && TT.isGNUEnvironment()) {
     setLibcallName(RTLIB::REM_F128, "fmodf128");