[MetaRenamer] Don't rename library functions.

[bryant]

Summary

I'm assuming is that bugpoint repros should behave the same before and after -metarenamer.

[davide]

You want to do this for all the external functions, maybe?

[bryant]

In D31304#709218, @davide wrote:

You want to do this for all the external functions, maybe?

Not sure that I understand. Externs are preserved with this patch. In the test case that I've added, for instance,

20:58:29 ~/3rd/llvm/test> opt -S -metarenamer Transforms/MetaRenamer/metarenamer.ll | tail -n 13
declare noalias i8* @malloc(i32)   <================

declare void @free(i8* nocapture)  <===============

define void @zot() {
bb:
  %tmp = call i8* @malloc(i32 23)
  call void @free(i8* %tmp)
  ret void
}

attributes #0 = { nounwind ssp uwtable }
attributes #1 = { argmemonly nounwind }

Am I missing your meaning?

[davide]

I mean, all external functions, not just libcalls, e.g.

declare noalias i8* @blahgoo(i32)  
[...]
  call void @blahgoo(i8* %tmp)

... unless they're already preserved, in which case, feel free to ignore this comment.

[bryant]

What happens if there's a conflict between a meta-renamed function and originally named extern? For instance,

declare void @pluto()

define void @dont_rename_lib_funcs(...) {  ; metarenames to pluto.
  ...
}

?

[davide]

In D31304#709304, @bryant wrote:

What happens if there's a conflict between a meta-renamed function and originally named extern? For instance,

declare void @pluto()

define void @dont_rename_lib_funcs(...) {  ; metarenames to pluto.
  ...
}

?

If I understand your example correctly, that's a bug in the pass?

[bryant]

What I mean is that I don't see the reason for wanting to keep non-lib externs. Lib externs, on the other hand, need to stay un-renamed because some passes may behave differently in the presence of specific library functions. DSE, for instance, provides special handling for malloc-ed memory locations.

[bryant]

In D31304#709318, @davide wrote:

In D31304#709304, @bryant wrote:

What happens if there's a conflict between a meta-renamed function and originally named extern? For instance,

declare void @pluto()

define void @dont_rename_lib_funcs(...) {  ; metarenames to pluto.
  ...
}

?

If I understand your example correctly, that's a bug in the pass?

Actually, I think it would rename dont_rename_lib_funcs to pluto.1, pluto.2, etc. as it does now when it runs out of meta names (and if it doesn't, it should). What I really meant to ask is the reply above.

[davide]

Oh, sure. Sounds sensible (modulo nits).

lib/Transforms/Utils/MetaRenamer.cpp

118–124

Add a comment explaining why you're skipping funcs.

test/Transforms/MetaRenamer/metarenamer.ll

104–105

; CHECK-LABEL:
; CHECK-NEXT:
; CHECK-NEXT:

[bryant]

• Explain why leave lib funcs alone.
• Make test case FileChecks complete..

lib/Transforms/Utils/MetaRenamer.cpp

 // this pass after bugpoint reduction to conceal the nature of the original
 // program.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/IPO.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/TypeFinder.h"
 #include "llvm/Pass.h"
 using namespace llvm;
 
namespace {
   
   struct MetaRenamer : public ModulePass {
     static char ID; // Pass identification, replacement for typeid
     MetaRenamer() : ModulePass(ID) {
       initializeMetaRenamerPass(*PassRegistry::getPassRegistry());
     }
 
     void getAnalysisUsage(AnalysisUsage &AU) const override {
+      AU.addRequired<TargetLibraryInfoWrapperPass>();
       AU.setPreservesAll();
     }
 
     bool runOnModule(Module &M) override {
       // Seed our PRNG with simple additive sum of ModuleID. We're looking to
       // simply avoid always having the same function names, and we need to
       // remain deterministic.
       unsigned int randSeed = 0;
bool runOnModule(Module &M) override {
         if (STy->isLiteral() || STy->getName().empty()) continue;
 
         SmallString<128> NameStorage;
         STy->setName((Twine("struct.") +
           renamer.newName()).toStringRef(NameStorage));
       }
 
       // Rename all functions
+      const TargetLibraryInfo &TLI =
+          getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
       for (auto &F : M) {
         StringRef Name = F.getName();
-        if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1))
+        LibFunc Tmp;
+        // Leave library functions alone because their presence or absence could
+        // affect the behavior of other passes.
+        if (Name.startswith("llvm.") || (!Name.empty() && Name[0] == 1) ||
+            TLI.getLibFunc(F, Tmp))
           continue;
 
         F.setName(renamer.newName());
         runOnFunction(F);
       }
       return true;
     }
 
     bool runOnFunction(Function &F) {
bool runOnFunction(Function &F) {
             I.setName("tmp");
       }
       return true;
     }
   };
 }
 
 char MetaRenamer::ID = 0;
-INITIALIZE_PASS(MetaRenamer, "metarenamer", 
+INITIALIZE_PASS_BEGIN(MetaRenamer, "metarenamer",
+                      "Assign new names to everything", false, false)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_END(MetaRenamer, "metarenamer",
                     "Assign new names to everything", false, false)
 //===----------------------------------------------------------------------===//
 //
 // MetaRenamer - Rename everything with metasyntactic names.
 //
 ModulePass *llvm::createMetaRenamerPass() {
   return new MetaRenamer();
 }

test/Transforms/MetaRenamer/metarenamer.ll

 
 define i32 @varargs_func_6_xxx(i32 %arg_1_xxx, i32 %arg_2_xxx, ...) nounwind uwtable ssp {
   %1 = alloca i32, align 4
   %2 = alloca i32, align 4
   store i32 %arg_1_xxx, i32* %1, align 4
   store i32 %arg_2_xxx, i32* %2, align 4
   ret i32 6
 }
+
+declare noalias i8* @malloc(i32)
+declare void @free(i8* nocapture)
+
+define void @dont_rename_lib_funcs() {
+; CHECK-LABEL: @foo(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    [[TMP:%.*]] = call i8* @malloc(i32 23)
+; CHECK-NEXT:    call void @free(i8* [[TMP]])
+; CHECK-NEXT:    ret void
+;
+  %x = call i8* @malloc(i32 23)
+  call void @free(i8* %x)
+  ret void
+}