[llvm] RuntimeLibcalls: Split lowering decisions into LibcallLoweringInfo (PR #164987)

[Saleem Abdulrasool via llvm-commits]

================
@@ -0,0 +1,65 @@
+//===- LibcallLoweringInfo.h ------------------------------------*- C++ -*-===//
+//
+// 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/IR/RuntimeLibcalls.h"
+
+namespace llvm {
+
+class LibcallLoweringInfo {
+private:
+  LLVM_ABI const RTLIB::RuntimeLibcallsInfo &RTLCI;
+  /// Stores the implementation choice for each each libcall.
+  LLVM_ABI RTLIB::LibcallImpl LibcallImpls[RTLIB::UNKNOWN_LIBCALL + 1] = {
+      RTLIB::Unsupported};
+
+public:
+  LLVM_ABI LibcallLoweringInfo(const RTLIB::RuntimeLibcallsInfo &RTLCI);
+
+  /// Get the libcall routine name for the specified libcall.
+  // FIXME: This should be removed. Only LibcallImpl should have a name.
+  LLVM_ABI const char *getLibcallName(RTLIB::Libcall Call) const {
+    // FIXME: Return StringRef
+    return RTLIB::RuntimeLibcallsInfo::getLibcallImplName(LibcallImpls[Call])
+        .data();
+  }
+
+  /// Return the lowering's selection of implementation call for \p Call
+  LLVM_ABI RTLIB::LibcallImpl getLibcallImpl(RTLIB::Libcall Call) const {
+    return LibcallImpls[Call];
+  }
+
+  /// Rename the default libcall routine name for the specified libcall.
+  LLVM_ABI void setLibcallImpl(RTLIB::Libcall Call, RTLIB::LibcallImpl Impl) {
+    LibcallImpls[Call] = Impl;
+  }
+
+  // FIXME: Remove this wrapper in favor of directly using
+  // getLibcallImplCallingConv
+  LLVM_ABI CallingConv::ID getLibcallCallingConv(RTLIB::Libcall Call) const {
+    return RTLCI.LibcallImplCallingConvs[LibcallImpls[Call]];
+  }
+
+  /// Get the CallingConv that should be used for the specified libcall.
+  LLVM_ABI CallingConv::ID
+  getLibcallImplCallingConv(RTLIB::LibcallImpl Call) const {
+    return RTLCI.LibcallImplCallingConvs[Call];
+  }
+
+  /// Return a function name compatible with RTLIB::MEMCPY, or nullptr if fully
+  /// unsupported.
+  LLVM_ABI StringRef getMemcpyName() const {
+    RTLIB::LibcallImpl Memcpy = getLibcallImpl(RTLIB::MEMCPY);
+    if (Memcpy != RTLIB::Unsupported)
+      return RTLIB::RuntimeLibcallsInfo::getLibcallImplName(Memcpy);
+
+    // Fallback to memmove if memcpy isn't available.
+    return getLibcallName(RTLIB::MEMMOVE);
----------------
compnerd wrote:

Inverting this would be more LLVM style:


```suggestion
    RTLIB::LibcallImpl Memcpy = getLibcallImpl(RTLIB::MEMCPY);
    if (Memcpy == RTLIB::Unsupported)
      // Fallback to memmove if memcpy isn't available.
      return getLibcallName(RTLIB::MEMMOVE);
    return RTLIB::RuntimeLibcallsInfo::getLibcallImplName(Memcpy);


```

https://github.com/llvm/llvm-project/pull/164987