[Mlir-commits] [clang] [flang] [llvm] [mlir] [Transforms] Introduce BuildBuiltins.h atomic helpers (PR #101966)

[Tom Eccles]

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@@ -0,0 +1,826 @@
+//===- BuildBuiltins.cpp - Utility builder for builtins -------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/BuildBuiltins.h"
+#include "llvm/CodeGen/TargetLowering.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/Transforms/Utils/BuildLibCalls.h"
+
+using namespace llvm;
+
+namespace {
+static IntegerType *getIntTy(IRBuilderBase &B, const TargetLibraryInfo *TLI) {
+  return B.getIntNTy(TLI->getIntSize());
+}
+
+static IntegerType *getSizeTTy(IRBuilderBase &B, const TargetLibraryInfo *TLI) {
+  const Module *M = B.GetInsertBlock()->getModule();
+  return B.getIntNTy(TLI->getSizeTSize(*M));
+}
+
+/// In order to use one of the sized library calls such as
+/// __atomic_fetch_add_4, the alignment must be sufficient, the size
+/// must be one of the potentially-specialized sizes, and the value
+/// type must actually exist in C on the target (otherwise, the
+/// function wouldn't actually be defined.)
+static bool canUseSizedAtomicCall(unsigned Size, Align Alignment,
+                                  const DataLayout &DL) {
+  // TODO: "LargestSize" is an approximation for "largest type that
+  // you can express in C". It seems to be the case that int128 is
+  // supported on all 64-bit platforms, otherwise only up to 64-bit
+  // integers are supported. If we get this wrong, then we'll try to
+  // call a sized libcall that doesn't actually exist. There should
+  // really be some more reliable way in LLVM of determining integer
+  // sizes which are valid in the target's C ABI...
+  unsigned LargestSize = DL.getLargestLegalIntTypeSizeInBits() >= 64 ? 16 : 8;
+  return Alignment >= Size &&
+         (Size == 1 || Size == 2 || Size == 4 || Size == 8 || Size == 16) &&
+         Size <= LargestSize;
+}
+
+// Helper to check if a type is in a variant
+template <typename T, typename Variant> struct is_in_variant;
+
+template <typename T, typename... Types>
+struct is_in_variant<T, std::variant<Types...>>
+    : std::disjunction<std::is_same<T, Types>...> {};
+
+/// Alternative to std::holds_alternative that works even if the std::variant
+/// cannot hold T.
+template <typename T, typename Variant>
+constexpr bool holds_alternative_if_exists(const Variant &v) {
+  if constexpr (is_in_variant<T, Variant>::value) {
+    return std::holds_alternative<T>(v);
+  } else {
+    // Type T is not in the variant, return false or handle accordingly
+    return false;
+  }
+}
+
+/// Common code for emitting an atomic builtin (load, store, cmpxchg).
+class AtomicEmitter {
----------------
tblah wrote:

I have a warning here "AtomicEmitter has virtual functions but non-virtual destructor".

https://github.com/llvm/llvm-project/pull/101966