[BPF] Define set of BPF libcalls

Author: LucasSte

llvm/include/llvm/IR/RuntimeLibcalls.td

@@ -2808,6 +2808,23 @@ def WasmSystemLibrary
            emscripten_return_address,
            __stack_chk_fail, __stack_chk_guard)>;
 
+//===----------------------------------------------------------------------===//
+// BPF Runtime Libcalls
+//===----------------------------------------------------------------------===//
+
+def isBPF : RuntimeLibcallPredicate<"TT.isBPF()">;
+
+def BPFSystemLibrary
+    : SystemRuntimeLibrary<isBPF,
+      (add (sub DefaultRuntimeLibcallImpls,
+      // i128 operations should be lowered by LLVM for BPF
+       __divti3,
+       __udivti3,
+       __modti3,
+       __umodti3,
+       __clzti2
+    ))>;
+
 //===----------------------------------------------------------------------===//
 // Legacy Default Runtime Libcalls
 //===----------------------------------------------------------------------===//

llvm/test/CodeGen/BPF/builtin_calls.ll

@@ -0,0 +1,23 @@
+; RUN: llc -march=bpfel < %s | FileCheck %s
+;
+; C code for this test case:
+;
+; long func(long a, long b) {
+;     long x;
+;     return __builtin_mul_overflow(a, b, &x);
+; }
+
+
+declare { i64, i1 } @llvm.smul.with.overflow.i64(i64, i64)
+
+define noundef range(i64 0, 2) i64 @func(i64 noundef %a, i64 noundef %b) local_unnamed_addr {
+entry:
+  %0 = tail call { i64, i1 } @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
+  %1 = extractvalue { i64, i1 } %0, 1
+  %conv = zext i1 %1 to i64
+  ret i64 %conv
+}
+
+; CHECK-LABEL: func
+; CHECK-NOT: call __multi3
+; CHECK: exit