[llvm] 1915fa1 - Utils: Add pass to declare runtime libcalls (#147534)

[via llvm-commits]

Author: Matt Arsenault
Date: 2025-07-09T00:52:22+09:00
New Revision: 1915fa15c39e056a44d9c866d1e8dde4211d774d

URL: https://github.com/llvm/llvm-project/commit/1915fa15c39e056a44d9c866d1e8dde4211d774d
DIFF: https://github.com/llvm/llvm-project/commit/1915fa15c39e056a44d9c866d1e8dde4211d774d.diff

LOG: Utils: Add pass to declare runtime libcalls (#147534)

This will be useful for testing the set of calls for different systems,
and eventually the product of context specific modifiers applied. In
the future we should also know the type signatures, and be able to
emit the correct one.

Added: 
    llvm/include/llvm/Transforms/Utils/DeclareRuntimeLibcalls.h
    llvm/lib/Transforms/Utils/DeclareRuntimeLibcalls.cpp
    llvm/test/Transforms/Util/DeclareRuntimeLibcalls/basic.ll

Modified: 
    llvm/lib/Passes/PassBuilder.cpp
    llvm/lib/Passes/PassRegistry.def
    llvm/lib/Transforms/Utils/CMakeLists.txt
    llvm/utils/gn/secondary/llvm/lib/Transforms/Utils/BUILD.gn

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/Transforms/Utils/DeclareRuntimeLibcalls.h b/llvm/include/llvm/Transforms/Utils/DeclareRuntimeLibcalls.h
new file mode 100644
index 0000000000000..295e3dec31415
--- /dev/null
+++ b/llvm/include/llvm/Transforms/Utils/DeclareRuntimeLibcalls.h
@@ -0,0 +1,23 @@
+//===- DeclareRuntimeLibcalls.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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_DECLARERUNTIMELIBCALLS_H
+#define LLVM_TRANSFORMS_UTILS_DECLARERUNTIMELIBCALLS_H
+
+#include "llvm/IR/PassManager.h"
+
+namespace llvm {
+class DeclareRuntimeLibcallsPass
+    : public PassInfoMixin<DeclareRuntimeLibcallsPass> {
+public:
+  PreservedAnalyses run(Module &M, ModuleAnalysisManager &MAM);
+};
+
+} // end namespace llvm
+
+#endif // LLVM_TRANSFORMS_UTILS_DECLARERUNTIMELIBCALLS_H

diff  --git a/llvm/lib/Passes/PassBuilder.cpp b/llvm/lib/Passes/PassBuilder.cpp
index 874fce05841e2..67800874b0a3f 100644
--- a/llvm/lib/Passes/PassBuilder.cpp
+++ b/llvm/lib/Passes/PassBuilder.cpp
@@ -339,6 +339,7 @@
 #include "llvm/Transforms/Utils/CountVisits.h"
 #include "llvm/Transforms/Utils/DXILUpgrade.h"
 #include "llvm/Transforms/Utils/Debugify.h"
+#include "llvm/Transforms/Utils/DeclareRuntimeLibcalls.h"
 #include "llvm/Transforms/Utils/EntryExitInstrumenter.h"
 #include "llvm/Transforms/Utils/FixIrreducible.h"
 #include "llvm/Transforms/Utils/HelloWorld.h"

diff  --git a/llvm/lib/Passes/PassRegistry.def b/llvm/lib/Passes/PassRegistry.def
index dd3dab3425975..96250772da4a0 100644
--- a/llvm/lib/Passes/PassRegistry.def
+++ b/llvm/lib/Passes/PassRegistry.def
@@ -70,6 +70,7 @@ MODULE_PASS("ctx-prof-flatten-prethinlink",
 MODULE_PASS("noinline-nonprevailing", NoinlineNonPrevailing())
 MODULE_PASS("deadargelim", DeadArgumentEliminationPass())
 MODULE_PASS("debugify", NewPMDebugifyPass())
+MODULE_PASS("declare-runtime-libcalls", DeclareRuntimeLibcallsPass())
 MODULE_PASS("dfsan", DataFlowSanitizerPass())
 MODULE_PASS("dot-callgraph", CallGraphDOTPrinterPass())
 MODULE_PASS("dxil-upgrade", DXILUpgradePass())

diff  --git a/llvm/lib/Transforms/Utils/CMakeLists.txt b/llvm/lib/Transforms/Utils/CMakeLists.txt
index 78cad0d253be8..f7e66eca6aeb3 100644
--- a/llvm/lib/Transforms/Utils/CMakeLists.txt
+++ b/llvm/lib/Transforms/Utils/CMakeLists.txt
@@ -20,6 +20,7 @@ add_llvm_component_library(LLVMTransformUtils
   CtorUtils.cpp
   CountVisits.cpp
   Debugify.cpp
+  DeclareRuntimeLibcalls.cpp
   DemoteRegToStack.cpp
   DXILUpgrade.cpp
   EntryExitInstrumenter.cpp

diff  --git a/llvm/lib/Transforms/Utils/DeclareRuntimeLibcalls.cpp b/llvm/lib/Transforms/Utils/DeclareRuntimeLibcalls.cpp
new file mode 100644
index 0000000000000..540039b7d2cbd
--- /dev/null
+++ b/llvm/lib/Transforms/Utils/DeclareRuntimeLibcalls.cpp
@@ -0,0 +1,38 @@
+//===- DeclareRuntimeLibcalls.cpp -----------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Insert declarations for all runtime library calls known for the target.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/DeclareRuntimeLibcalls.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/RuntimeLibcalls.h"
+
+using namespace llvm;
+
+PreservedAnalyses DeclareRuntimeLibcallsPass::run(Module &M,
+                                                  ModuleAnalysisManager &MAM) {
+  RTLIB::RuntimeLibcallsInfo RTLCI(M.getTargetTriple());
+  LLVMContext &Ctx = M.getContext();
+
+  for (RTLIB::LibcallImpl Impl : RTLCI.getLibcallImpls()) {
+    if (Impl == RTLIB::Unsupported)
+      continue;
+
+    // TODO: Declare with correct type, calling convention, and attributes.
+
+    FunctionType *FuncTy =
+        FunctionType::get(Type::getVoidTy(Ctx), {}, /*IsVarArgs=*/true);
+
+    const char *FuncName = RTLCI.getLibcallImplName(Impl);
+    M.getOrInsertFunction(FuncName, FuncTy);
+  }
+
+  return PreservedAnalyses::none();
+}

diff  --git a/llvm/test/Transforms/Util/DeclareRuntimeLibcalls/basic.ll b/llvm/test/Transforms/Util/DeclareRuntimeLibcalls/basic.ll
new file mode 100644
index 0000000000000..ee3a0539bf300
--- /dev/null
+++ b/llvm/test/Transforms/Util/DeclareRuntimeLibcalls/basic.ll
@@ -0,0 +1,15 @@
+; RUN: opt -S -passes=declare-runtime-libcalls -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s
+
+; Check an already declared function
+; CHECK: declare float @logf(float)
+declare float @logf(float)
+
+; Check an already defined function
+; CHECK: define float @sinf(float %x) {
+define float @sinf(float %x) {
+  ret float %x
+}
+
+; CHECK: declare void @acosf(...)
+; CHECK: declare void @__umodti3(...)
+

diff  --git a/llvm/utils/gn/secondary/llvm/lib/Transforms/Utils/BUILD.gn b/llvm/utils/gn/secondary/llvm/lib/Transforms/Utils/BUILD.gn
index b16fe19bddfd1..d327e810c536d 100644
--- a/llvm/utils/gn/secondary/llvm/lib/Transforms/Utils/BUILD.gn
+++ b/llvm/utils/gn/secondary/llvm/lib/Transforms/Utils/BUILD.gn
@@ -29,6 +29,7 @@ static_library("Utils") {
     "CtorUtils.cpp",
     "DXILUpgrade.cpp",
     "Debugify.cpp",
+    "DeclareRuntimeLibcalls.cpp",
     "DemoteRegToStack.cpp",
     "EntryExitInstrumenter.cpp",
     "EscapeEnumerator.cpp",