[LLVM][Analysis] Add a pass to print unknown intrinsics

Add a pass that will print unknown intrinsics, which is a function
whose name starts with `llvm.` but is not a intrinsic regonized by
LLVM.

This can help debug issues such as
https://github.com/StanfordLegion/legion/issues/1865#issuecomment-2863656342

Author: jurahul

llvm/include/llvm/Analysis/UnknownIntrinsicPrinter.h

@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_ANALYSIS_UNKNOWNINTRINSICPRINTER_H
+#define LLVM_ANALYSIS_UNKNOWNINTRINSICPRINTER_H
+
+#include "llvm/IR/PassManager.h"
+
+namespace llvm {
+class UnknownIntrinsicPrinterPass
+    : public PassInfoMixin<UnknownIntrinsicPrinterPass> {
+  raw_ostream &OS;
+
+public:
+  UnknownIntrinsicPrinterPass(raw_ostream &OS) : OS(OS) {}
+  PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
+  static bool isRequired() { return true; }
+};
+} // namespace llvm
+
+#endif // LLVM_ANALYSIS_UNKNOWNINTRINSICPRINTER_H

llvm/lib/Analysis/CMakeLists.txt

@@ -155,6 +155,7 @@ add_llvm_component_library(LLVMAnalysis
   TypeBasedAliasAnalysis.cpp
   TypeMetadataUtils.cpp
   UniformityAnalysis.cpp
+  UnknownIntrinsicPrinter.cpp
   ScopedNoAliasAA.cpp
   ValueLattice.cpp
   ValueLatticeUtils.cpp

llvm/lib/Analysis/UnknownIntrinsicPrinter.cpp

@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+// 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/Analysis/UnknownIntrinsicPrinter.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/Module.h"
+
+using namespace llvm;
+
+PreservedAnalyses UnknownIntrinsicPrinterPass::run(Module &M,
+                                                   ModuleAnalysisManager &) {
+  for (const Function &F : M.functions()) {
+    // An unknown intrinsic is a function that begins with "llvm." but is not
+    // a recognized intrinsic (i.e., it's IntrinsicID is not_intrinsic).
+    if (F.isIntrinsic() && F.getIntrinsicID() == Intrinsic::not_intrinsic)
+      OS << "Unknown intrinsic : " << F.getName() << '\n';
+  }
+  return PreservedAnalyses::all();
+}

llvm/lib/Passes/PassBuilder.cpp

@@ -77,6 +77,7 @@
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Analysis/TypeBasedAliasAnalysis.h"
 #include "llvm/Analysis/UniformityAnalysis.h"
+#include "llvm/Analysis/UnknownIntrinsicPrinter.h"
 #include "llvm/CodeGen/AssignmentTrackingAnalysis.h"
 #include "llvm/CodeGen/AtomicExpand.h"
 #include "llvm/CodeGen/BasicBlockSectionsProfileReader.h"

llvm/lib/Passes/PassRegistry.def

@@ -138,6 +138,7 @@ MODULE_PASS("print<inline-advisor>", InlineAdvisorAnalysisPrinterPass(errs()))
 MODULE_PASS("print<ir2vec>", IR2VecPrinterPass(errs()))
 MODULE_PASS("print<module-debuginfo>", ModuleDebugInfoPrinterPass(errs()))
 MODULE_PASS("print<reg-usage>", PhysicalRegisterUsageInfoPrinterPass(errs()))
+MODULE_PASS("print-unknown-intrinsics", UnknownIntrinsicPrinterPass(errs()))
 MODULE_PASS("pseudo-probe", SampleProfileProbePass(TM))
 MODULE_PASS("pseudo-probe-update", PseudoProbeUpdatePass())
 MODULE_PASS("recompute-globalsaa", RecomputeGlobalsAAPass())

llvm/test/Analysis/UnknownIntrinsicPrinter/unknown.ll

@@ -0,0 +1,25 @@
+; RUN: opt -disable-output -passes=print-unknown-intrinsics %s 2>&1 | FileCheck %s
+
+; ------------------------------------------------------------------------------
+; Add several known intrinsics.
+declare i8 @llvm.ctpop.i8(i8)
+declare double @llvm.sqrt.f64(double)
+
+; Note, the next two are known intrinsics because automatic remanging of
+; intrinsics will convert them to the "correct" name.
+
+; Remangled to llvm.sqrt.f64(double).
+declare double @llvm.sqrt.foo(double)
+
+; Remangled to llvm.ctpop.i8(i8).
+declare i8 @llvm.ctpop.unknown.i8(i8)
+
+; ------------------------------------------------------------------------------
+; Add several unknown intrinsics.
+declare i1 @llvm.isunordered.f32(float, float)
+declare i8 @llvm.foo.unknown.i8(i8)
+declare i8 @llvm.unknown.i8(i8)
+
+; CHECK: Unknown intrinsic : llvm.isunordered.f32
+; CHECK: Unknown intrinsic : llvm.foo.unknown.i8
+; CHECK: Unknown intrinsic : llvm.unknown.i8