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

Introduce a new class for the TargetLowering usage. This tracks the
subtarget specific lowering decisions for which libcall to use.
RuntimeLibcallsInfo is a module level property, which may have multiple
implementations of a particular libcall available. This attempts to be
a minimum boilerplate patch to introduce the new concept.

In the future we should have a tablegen way of selecting which
implementations should be used for a subtarget. Currently we
do have some conflicting implementations added, it just happens
to work out that the default cases to prefer is alphabetically
first (plus some of these still are using manual overrides
in TargetLowering constructors).

Author: arsenm

llvm/include/llvm/CodeGen/LibcallLoweringInfo.h

@@ -0,0 +1,66 @@
+//===- 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 impl compatible with RTLIB::MEMCPY, or
+  /// RTLIB::Unsupported if fully unsupported.
+  RTLIB::LibcallImpl getMemcpyImpl() const {
+    RTLIB::LibcallImpl Memcpy = getLibcallImpl(RTLIB::MEMCPY);
+    if (Memcpy == RTLIB::Unsupported) {
+      // Fallback to memmove if memcpy isn't available.
+      return getLibcallImpl(RTLIB::MEMMOVE);
+    }
+
+    return Memcpy;
+  }
+};
+
+} // end namespace llvm

llvm/include/llvm/CodeGen/TargetLowering.h

@@ -29,6 +29,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/CodeGen/DAGCombine.h"
 #include "llvm/CodeGen/ISDOpcodes.h"
+#include "llvm/CodeGen/LibcallLoweringInfo.h"
 #include "llvm/CodeGen/LowLevelTypeUtils.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/RuntimeLibcallUtil.h"
@@ -3597,7 +3598,7 @@ class LLVM_ABI TargetLoweringBase {
   }
 
   const RTLIB::RuntimeLibcallsInfo &getRuntimeLibcallsInfo() const {
-    return Libcalls;
+    return RuntimeLibcallInfo;
   }
 
   void setLibcallImpl(RTLIB::Libcall Call, RTLIB::LibcallImpl Impl) {
@@ -3610,9 +3611,9 @@ class LLVM_ABI TargetLoweringBase {
   }
 
   /// Get the libcall routine name for the specified libcall.
+  // FIXME: This should be removed. Only LibcallImpl should have a name.
   const char *getLibcallName(RTLIB::Libcall Call) const {
-    // FIXME: Return StringRef
-    return Libcalls.getLibcallName(Call).data();
+    return Libcalls.getLibcallName(Call);
   }
 
   /// Get the libcall routine name for the specified libcall implementation
@@ -3625,19 +3626,14 @@ class LLVM_ABI TargetLoweringBase {
   /// Check if this is valid libcall for the current module, otherwise
   /// RTLIB::Unsupported.
   RTLIB::LibcallImpl getSupportedLibcallImpl(StringRef FuncName) const {
-    return Libcalls.getSupportedLibcallImpl(FuncName);
+    return RuntimeLibcallInfo.getSupportedLibcallImpl(FuncName);
   }
 
   /// Get the comparison predicate that's to be used to test the result of the
   /// comparison libcall against zero. This should only be used with
   /// floating-point compare libcalls.
   ISD::CondCode getSoftFloatCmpLibcallPredicate(RTLIB::LibcallImpl Call) const;
 
-  /// Set the CallingConv that should be used for the specified libcall.
-  void setLibcallImplCallingConv(RTLIB::LibcallImpl Call, CallingConv::ID CC) {
-    Libcalls.setLibcallImplCallingConv(Call, CC);
-  }
-
   /// Get the CallingConv that should be used for the specified libcall
   /// implementation.
   CallingConv::ID getLibcallImplCallingConv(RTLIB::LibcallImpl Call) const {
@@ -3834,8 +3830,11 @@ class LLVM_ABI TargetLoweringBase {
   std::map<std::pair<unsigned, MVT::SimpleValueType>, MVT::SimpleValueType>
     PromoteToType;
 
+  /// FIXME: This should not live here; it should come from an analysis.
+  const RTLIB::RuntimeLibcallsInfo RuntimeLibcallInfo;
+
   /// The list of libcalls that the target will use.
-  RTLIB::RuntimeLibcallsInfo Libcalls;
+  LibcallLoweringInfo Libcalls;
 
   /// The bits of IndexedModeActions used to store the legalisation actions
   /// We store the data as   | ML | MS |  L |  S | each taking 4 bits.

llvm/include/llvm/IR/RuntimeLibcalls.h

@@ -42,6 +42,8 @@ template <> struct enum_iteration_traits<RTLIB::LibcallImpl> {
   static constexpr bool is_iterable = true;
 };
 
+class LibcallLoweringInfo;
+
 namespace RTLIB {
 
 // Return an iterator over all Libcall values.
@@ -70,6 +72,8 @@ struct RuntimeLibcallsInfo {
   LibcallImplBitset AvailableLibcallImpls;
 
 public:
+  friend class llvm::LibcallLoweringInfo;
+
   explicit RuntimeLibcallsInfo(
       const Triple &TT,
       ExceptionHandling ExceptionModel = ExceptionHandling::None,
@@ -85,17 +89,6 @@ struct RuntimeLibcallsInfo {
     initLibcalls(TT, ExceptionModel, FloatABI, EABIVersion, ABIName);
   }
 
-  /// Rename the default libcall routine name for the specified libcall.
-  void setLibcallImpl(RTLIB::Libcall Call, RTLIB::LibcallImpl Impl) {
-    LibcallImpls[Call] = Impl;
-  }
-
-  /// Get the libcall routine name for the specified libcall.
-  // FIXME: This should be removed. Only LibcallImpl should have a name.
-  StringRef getLibcallName(RTLIB::Libcall Call) const {
-    return getLibcallImplName(LibcallImpls[Call]);
-  }
-
   /// Get the libcall routine name for the specified libcall implementation.
   static StringRef getLibcallImplName(RTLIB::LibcallImpl CallImpl) {
     if (CallImpl == RTLIB::Unsupported)
@@ -105,42 +98,24 @@ struct RuntimeLibcallsInfo {
                      RuntimeLibcallNameSizeTable[CallImpl]);
   }
 
-  /// Return the lowering's selection of implementation call for \p Call
-  RTLIB::LibcallImpl getLibcallImpl(RTLIB::Libcall Call) const {
-    return LibcallImpls[Call];
-  }
-
   /// Set the CallingConv that should be used for the specified libcall
   /// implementation
   void setLibcallImplCallingConv(RTLIB::LibcallImpl Call, CallingConv::ID CC) {
     LibcallImplCallingConvs[Call] = CC;
   }
 
-  // FIXME: Remove this wrapper in favor of directly using
-  // getLibcallImplCallingConv
-  CallingConv::ID getLibcallCallingConv(RTLIB::Libcall Call) const {
-    return LibcallImplCallingConvs[LibcallImpls[Call]];
-  }
-
   /// Get the CallingConv that should be used for the specified libcall.
   CallingConv::ID getLibcallImplCallingConv(RTLIB::LibcallImpl Call) const {
     return LibcallImplCallingConvs[Call];
   }
 
-  ArrayRef<RTLIB::LibcallImpl> getLibcallImpls() const {
-    // Trim UNKNOWN_LIBCALL from the back
-    return ArrayRef(LibcallImpls).drop_back();
+  /// Return the libcall provided by \p Impl
+  static RTLIB::Libcall getLibcallFromImpl(RTLIB::LibcallImpl Impl) {
+    return ImplToLibcall[Impl];
   }
 
-  /// Return a function name compatible with RTLIB::MEMCPY, or nullptr if fully
-  /// unsupported.
-  RTLIB::LibcallImpl getMemcpyImpl() const {
-    RTLIB::LibcallImpl Memcpy = getLibcallImpl(RTLIB::MEMCPY);
-    if (Memcpy != RTLIB::Unsupported)
-      return Memcpy;
-
-    // Fallback to memmove if memcpy isn't available.
-    return getLibcallImpl(RTLIB::MEMMOVE);
+  unsigned getNumAvailableLibcallImpls() const {
+    return AvailableLibcallImpls.count();
   }
 
   bool isAvailable(RTLIB::LibcallImpl Impl) const {
@@ -151,11 +126,6 @@ struct RuntimeLibcallsInfo {
     AvailableLibcallImpls.set(Impl);
   }
 
-  /// Return the libcall provided by \p Impl
-  static RTLIB::Libcall getLibcallFromImpl(RTLIB::LibcallImpl Impl) {
-    return ImplToLibcall[Impl];
-  }
-
   /// Check if a function name is a recognized runtime call of any kind. This
   /// does not consider if this call is available for any current compilation,
   /// just that it is a known call somewhere. This returns the set of all
@@ -176,11 +146,8 @@ struct RuntimeLibcallsInfo {
   LLVM_ABI RTLIB::LibcallImpl
       getSupportedLibcallImpl(StringRef FuncName) const {
     for (RTLIB::LibcallImpl Impl : lookupLibcallImplName(FuncName)) {
-      // FIXME: This should not depend on looking up ImplToLibcall, only the
-      // list of libcalls for the module.
-      RTLIB::LibcallImpl Recognized = LibcallImpls[ImplToLibcall[Impl]];
-      if (Recognized != RTLIB::Unsupported)
-        return Recognized;
+      if (isAvailable(Impl))
+        return Impl;
     }
 
     return RTLIB::Unsupported;
@@ -197,10 +164,6 @@ struct RuntimeLibcallsInfo {
   LLVM_ABI static iota_range<RTLIB::LibcallImpl>
   lookupLibcallImplNameImpl(StringRef Name);
 
-  /// Stores the implementation choice for each each libcall.
-  RTLIB::LibcallImpl LibcallImpls[RTLIB::UNKNOWN_LIBCALL + 1] = {
-      RTLIB::Unsupported};
-
   static_assert(static_cast<int>(CallingConv::C) == 0,
                 "default calling conv should be encoded as 0");
 
@@ -274,6 +237,7 @@ struct RuntimeLibcallsInfo {
 };
 
 } // namespace RTLIB
+
 } // namespace llvm
 
 #endif // LLVM_IR_RUNTIME_LIBCALLS_H

llvm/lib/CodeGen/CMakeLists.txt

@@ -88,6 +88,7 @@ add_llvm_component_library(LLVMCodeGen
   LatencyPriorityQueue.cpp
   LazyMachineBlockFrequencyInfo.cpp
   LexicalScopes.cpp
+  LibcallLoweringInfo.cpp
   LiveDebugVariables.cpp
   LiveIntervals.cpp
   LiveInterval.cpp

llvm/lib/CodeGen/LibcallLoweringInfo.cpp

@@ -0,0 +1,26 @@
+//===- LibcallLoweringInfo.cpp - Interface for runtime libcalls -----------===//
+//
+// 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/CodeGen/LibcallLoweringInfo.h"
+
+using namespace llvm;
+
+LibcallLoweringInfo::LibcallLoweringInfo(
+    const RTLIB::RuntimeLibcallsInfo &RTLCI)
+    : RTLCI(RTLCI) {
+  // TODO: This should be generated with lowering predicates, and assert the
+  // call is available.
+  for (RTLIB::LibcallImpl Impl : RTLIB::libcall_impls()) {
+    if (RTLCI.isAvailable(Impl)) {
+      RTLIB::Libcall LC = RTLIB::RuntimeLibcallsInfo::getLibcallFromImpl(Impl);
+      // FIXME: Hack, assume the first available libcall wins.
+      if (LibcallImpls[LC] == RTLIB::Unsupported)
+        LibcallImpls[LC] = Impl;
+    }
+  }
+}

llvm/lib/CodeGen/TargetLoweringBase.cpp

@@ -697,9 +697,11 @@ ISD::CondCode TargetLoweringBase::getSoftFloatCmpLibcallPredicate(
 
 /// NOTE: The TargetMachine owns TLOF.
 TargetLoweringBase::TargetLoweringBase(const TargetMachine &tm)
-    : TM(tm), Libcalls(TM.getTargetTriple(), TM.Options.ExceptionModel,
-                       TM.Options.FloatABIType, TM.Options.EABIVersion,
-                       TM.Options.MCOptions.getABIName()) {
+    : TM(tm),
+      RuntimeLibcallInfo(TM.getTargetTriple(), TM.Options.ExceptionModel,
+                         TM.Options.FloatABIType, TM.Options.EABIVersion,
+                         TM.Options.MCOptions.getABIName()),
+      Libcalls(RuntimeLibcallInfo) {
   initActions();
 
   // Perform these initializations only once.

llvm/lib/IR/RuntimeLibcalls.cpp

@@ -19,6 +19,7 @@
 using namespace llvm;
 using namespace RTLIB;
 
+#define GET_RUNTIME_LIBCALLS_INFO
 #define GET_INIT_RUNTIME_LIBCALL_NAMES
 #define GET_SET_TARGET_RUNTIME_LIBCALL_SETS
 #define DEFINE_GET_LOOKUP_LIBCALL_IMPL_NAME

llvm/lib/LTO/LTO.cpp

@@ -1396,11 +1396,10 @@ Error LTO::runRegularLTO(AddStreamFn AddStream) {
 SmallVector<const char *> LTO::getRuntimeLibcallSymbols(const Triple &TT) {
   RTLIB::RuntimeLibcallsInfo Libcalls(TT);
   SmallVector<const char *> LibcallSymbols;
-  ArrayRef<RTLIB::LibcallImpl> LibcallImpls = Libcalls.getLibcallImpls();
-  LibcallSymbols.reserve(LibcallImpls.size());
+  LibcallSymbols.reserve(Libcalls.getNumAvailableLibcallImpls());
 
-  for (RTLIB::LibcallImpl Impl : LibcallImpls) {
-    if (Impl != RTLIB::Unsupported)
+  for (RTLIB::LibcallImpl Impl : RTLIB::libcall_impls()) {
+    if (Libcalls.isAvailable(Impl))
       LibcallSymbols.push_back(Libcalls.getLibcallImplName(Impl).data());
   }
 

llvm/lib/Target/WebAssembly/WebAssemblyRuntimeLibcallSignatures.cpp

@@ -532,13 +532,19 @@ struct StaticLibcallNameMap {
     // FIXME: This is broken if there are ever different triples compiled with
     // different libcalls.
     RTLIB::RuntimeLibcallsInfo RTCI(TT);
-    for (RTLIB::Libcall LC : RTLIB::libcalls()) {
-      StringRef NameLibcall = RTCI.getLibcallName(LC);
-      if (!NameLibcall.empty() &&
-          getRuntimeLibcallSignatures().Table[LC] != unsupported) {
-        assert(!Map.contains(NameLibcall) &&
-               "duplicate libcall names in name map");
-        Map[NameLibcall] = LC;
+
+    ArrayRef<RuntimeLibcallSignature> Table =
+        getRuntimeLibcallSignatures().Table;
+    for (RTLIB::LibcallImpl Impl : RTLIB::libcall_impls()) {
+      if (!RTCI.isAvailable(Impl))
+        continue;
+      RTLIB::Libcall LC = RTLIB::RuntimeLibcallsInfo::getLibcallFromImpl(Impl);
+      if (Table[LC] != unsupported) {
+        StringRef NameLibcall =
+            RTLIB::RuntimeLibcallsInfo::getLibcallImplName(Impl);
+        // FIXME: Map should be to LibcallImpl
+        if (!Map.insert({NameLibcall, LC}).second)
+          llvm_unreachable("duplicate libcall names in name map");
       }
     }
   }

llvm/lib/Transforms/Utils/DeclareRuntimeLibcalls.cpp

@@ -54,8 +54,8 @@ PreservedAnalyses DeclareRuntimeLibcallsPass::run(Module &M,
   const DataLayout &DL = M.getDataLayout();
   const Triple &TT = M.getTargetTriple();
 
-  for (RTLIB::LibcallImpl Impl : RTLCI.getLibcallImpls()) {
-    if (Impl == RTLIB::Unsupported)
+  for (RTLIB::LibcallImpl Impl : RTLIB::libcall_impls()) {
+    if (!RTLCI.isAvailable(Impl))
       continue;
 
     auto [FuncTy, FuncAttrs] = RTLCI.getFunctionTy(Ctx, TT, DL, Impl);