[FuncSpec] Don't specialize functions with attribute NoDuplicate.

[SjoerdMeijer]

Fixed typo in test.

[ChuanqiXu]

It makes sense to me. If a function is marked with NoDuplicate, we shouldn't clone it. Everything is fine.
But I want to ask, in what situations, generally a function would be marked with NoDuplicate attribute? I didn't find it in docs or codes.

[SjoerdMeijer]

In D104378#2823573, @ChuanqiXu wrote:

It makes sense to me. If a function is marked with NoDuplicate, we shouldn't clone it. Everything is fine.
But I want to ask, in what situations, generally a function would be marked with NoDuplicate attribute? I didn't find it in docs or codes.

In Clang, there's a no duplicate function attribute, see https://clang.llvm.org/docs/AttributeReference.html#noduplicate.
And that can translate to LLVM IR function attribute no duplicate, see also https://llvm.org/docs/LangRef.html#function-attributes.

[ChuanqiXu]

In D104378#2823877, @SjoerdMeijer wrote:

In D104378#2823573, @ChuanqiXu wrote:

It makes sense to me. If a function is marked with NoDuplicate, we shouldn't clone it. Everything is fine.
But I want to ask, in what situations, generally a function would be marked with NoDuplicate attribute? I didn't find it in docs or codes.

In Clang, there's a no duplicate function attribute, see https://clang.llvm.org/docs/AttributeReference.html#noduplicate.
And that can translate to LLVM IR function attribute no duplicate, see also https://llvm.org/docs/LangRef.html#function-attributes.

I see. Got it.

llvm/lib/Transforms/IPO/FunctionSpecialization.cpp

bool llvm::runFunctionSpecialization(
   FunctionSpecializer FS(Solver, GetAC, GetTTI, GetTLI);
   bool Changed = false;
 
   // Loop over all functions, marking arguments to those with their addresses
   // taken or that are external as overdefined.
   for (Function &F : M) {
     if (F.isDeclaration())
       continue;
+    if (F.hasFnAttribute(Attribute::NoDuplicate))
+      continue;
 
     LLVM_DEBUG(dbgs() << "\nFnSpecialization: Analysing decl: " << F.getName()
                       << "\n");
     Solver.addAnalysis(F, GetAnalysis(F));
 
     // Determine if we can track the function's arguments. If so, add the
     // function to the solver's set of argument-tracked functions.
     if (canTrackArgumentsInterprocedurally(&F)) {

llvm/test/Transforms/FunctionSpecialization/function-specialization-nodup.ll

+; RUN: opt -function-specialization -force-function-specialization -S < %s | FileCheck %s
+
+; Function @foo has function attribute 'noduplicate', so check that we don't
+; specialize it:
+
+; CHECK-NOT: @foo.1(
+; CHECK-NOT: @foo.2(
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+
+@A = external dso_local constant i32, align 4
+@B = external dso_local constant i32, align 4
+
+define dso_local i32 @bar(i32 %x, i32 %y) {
+entry:
+  %tobool = icmp ne i32 %x, 0
+  br i1 %tobool, label %if.then, label %if.else
+
+if.then:
+  %call = call i32 @foo(i32 %x, i32* @A)
+  br label %return
+
+if.else:
+  %call1 = call i32 @foo(i32 %y, i32* @B)
+  br label %return
+
+return:
+  %retval.0 = phi i32 [ %call, %if.then ], [ %call1, %if.else ]
+  ret i32 %retval.0
+}
+
+define internal i32 @foo(i32 %x, i32* %b) #0 {
+entry:
+  %0 = load i32, i32* %b, align 4
+  %add = add nsw i32 %x, %0
+  ret i32 %add
+}
+
+attributes #0 = { noduplicate }