[SOL] Allow selectively disable compiler builtins for BPF target (#4)

* [BPF] Add method to check whether a triple is a BPF architecture

* [BPF] Make rust allocation builtins unavailable for BPF target

- the calls to rust alloc/dealloc routines need to be preserved and
not replaced by compiler generated builtin inlined code

Author: dmakarov

llvm/include/llvm/ADT/Triple.h

@@ -738,6 +738,11 @@ class Triple {
                : PointerWidth == 64;
   }
 
+  /// Tests whether the target is BPF (little and big endian).
+  bool isBPF() const {
+    return getArch() == Triple::bpfel || getArch() == Triple::bpfeb;
+  }
+
   /// Tests whether the target is MIPS 32-bit (little and big endian).
   bool isMIPS32() const {
     return getArch() == Triple::mips || getArch() == Triple::mipsel;

llvm/lib/Analysis/TargetLibraryInfo.cpp

@@ -628,6 +628,12 @@ static void initialize(TargetLibraryInfoImpl &TLI, const Triple &T,
     TLI.setUnavailable(LibFunc_vec_free);
   }
 
+  if (T.isBPF()) {
+    TLI.setUnavailable(LibFunc_rust_alloc);
+    TLI.setUnavailable(LibFunc_rust_dealloc);
+    TLI.setUnavailable(LibFunc_rust_realloc);
+  }
+
   TLI.addVectorizableFunctionsFromVecLib(ClVectorLibrary);
 }