[BPF] Define set of BPF libcalls

Author: LucasSte

llvm/include/llvm/IR/RuntimeLibcalls.td

@@ -3464,13 +3464,22 @@ def WasmSystemLibrary
            emscripten_return_address,
            __stack_chk_fail, __stack_chk_guard)>;
 
+//===----------------------------------------------------------------------===//
+// BPF Runtime Libcalls
+//===----------------------------------------------------------------------===//
+
+def isBPF : RuntimeLibcallPredicate<"TT.isBPF()">;
+
+// No calls.
+def BPFSystemLibrary : SystemRuntimeLibrary<isBPF, (add)>;
+
 //===----------------------------------------------------------------------===//
 // Legacy Default Runtime Libcalls
 //===----------------------------------------------------------------------===//
 
 // TODO: Should make every target explicit.
 def isDefaultLibcallArch : RuntimeLibcallPredicate<[{
-  TT.isMIPS() || TT.isLoongArch() || TT.isVE() || TT.isBPF() ||
+  TT.isMIPS() || TT.isLoongArch() || TT.isVE() ||
   TT.getArch() == Triple::csky || TT.getArch() == Triple::arc ||
   TT.getArch() == Triple::m68k ||  TT.getArch() == Triple::xtensa ||
   (TT.isSystemZ() && !TT.isOSzOS())

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