[llvm-reduce] Function body reduction: don't forget to unset comdat

[Tyker]

Summary

althought the interstingness test should usually fail when the module is invalid
this changes reduces the frequency at which llvm-reduce generate invalid IR.

[lebedev.ri]

Needs two tests - i agree that comdat makes sense, but i'm not sure about linkage.

[Tyker]

In D86404#2232128, @lebedev.ri wrote:

Needs two tests - i agree that comdat makes sense, but i'm not sure about linkage.

always setting it to external is perhaps not the best decision here but some linkages like linkonce_odr are only valid on definitions.

[lebedev.ri]

After looking a bit more, i believe deleteBody() should do that.

llvm/tools/llvm-reduce/deltas/ReduceFunctionBodies.cpp

33

Actually, deleteBody() already does that.

[Tyker]

yeah linkage was already changed.
added a test

[lebedev.ri]

LGTM.
It's an improvement, but i really think this should be moved into deleteBody() itself.

I believe you might also need to fix basic block and instruction reducers - can they not end up deleting everything?

llvm/test/Reduce/remove-function-bodies-comdat.ll

3

Should we also check that the opt -verify passes?

[lebedev.ri]

Commit this? It's an improvement anyways.

llvm/test/Reduce/remove-function-bodies-comdat.ll

+; RUN: llvm-reduce --test FileCheck --test-arg --check-prefixes=CHECK-ALL,CHECK-INTERESTINGNESS --test-arg %s --test-arg --input-file %s -o %t
+; RUN: cat %t | FileCheck --check-prefixes=CHECK-ALL,CHECK-FINAL %s
+; RUN: opt -verify %t
+
+; CHECK-FINAL-NOT: = comdat
+; CHECK-INTERESTINGNESS: @callee(
+; CHECK-FINAL: declare void @callee()
+
+$foo = comdat any
+
+define void @callee() comdat($foo) {
+  ret void
+}
+
+; CHECK-ALL: define void @caller()
+define void @caller() {
+entry:
+; CHECK-ALL: call void @callee()
+; CHECK-ALL: ret void
+  call void @callee()
+  ret void
+}

llvm/tools/llvm-reduce/deltas/ReduceFunctionBodies.cpp

 //===- ReduceFunctions.cpp - Specialized Delta Pass -----------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements a function which calls the Generic Delta pass in order
 // to reduce function bodies in the provided Module.
 //
 //===----------------------------------------------------------------------===//
 
 #include "ReduceFunctionBodies.h"
 #include "Delta.h"
+#include "llvm/IR/GlobalValue.h"
 
 using namespace llvm;
 
 /// Removes all the bodies of defined functions that aren't inside any of the
 /// desired Chunks.
 static void
 extractFunctionBodiesFromModule(const std::vector<Chunk> &ChunksToKeep,
                                 Module *Program) {
   Oracle O(ChunksToKeep);
 
   // Delete out-of-chunk function bodies
   std::vector<Function *> FuncDefsToReduce;
   for (auto &F : *Program)
-    if (!F.isDeclaration() && !O.shouldKeep())
+    if (!F.isDeclaration() && !O.shouldKeep()) {
       F.deleteBody();
+      F.setComdat(nullptr);
+    }
 }
 
 /// Counts the amount of non-declaration functions and prints their
 /// respective name & index
 static int countFunctionDefinitions(Module *Program) {
   // TODO: Silence index with --quiet flag
   errs() << "----------------------------\n";
   errs() << "Function Definition Index Reference:\n";