[LLVMbugs] [Bug 8092] New: llvm.init.trampoline doesn't work if the function argument is a function pointer.

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=8092

           Summary: llvm.init.trampoline doesn't work if the function
                    argument is a function pointer.
           Product: new-bugs
           Version: trunk
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: fvbommel at wxs.nl
                CC: llvmbugs at cs.uiuc.edu


Created an attachment (id=5460)
 --> (http://llvm.org/bugs/attachment.cgi?id=5460)
A wrapper around llvm.init.trampoline

The attached .ll file contains a function calling llvm.init.trampoline, passing
its own arguments on to it. LLVM doesn't like this:
=====
$ llc make_trampoline.ll
llvm.init_trampoline parameter #2 must resolve to a function.
  %tramp = tail call i8* @llvm.init.trampoline(i8* %mem, i8* %fn, i8* %data)
Broken module found, compilation aborted!
0  llc             0x0000000000da92df
1  llc             0x0000000000dab552
2  libpthread.so.0 0x00007fa4ab8b78f0
3  libc.so.6       0x00007fa4aaba6a75 gsignal + 53
4  libc.so.6       0x00007fa4aabaa5c0 abort + 384
5  llc             0x0000000000d2160b
6  llc             0x0000000000cfb6cd
llvm::FPPassManager::runOnFunction(llvm::Function&) + 557
7  llc             0x0000000000cfb7cb
llvm::FPPassManager::runOnModule(llvm::Module&) + 75
8  llc             0x0000000000cfb257
llvm::MPPassManager::runOnModule(llvm::Module&) + 503
9  llc             0x0000000000cfb3d7 llvm::PassManagerImpl::run(llvm::Module&)
+ 167
10 llc             0x000000000053744d main + 4109
11 libc.so.6       0x00007fa4aab91c4d __libc_start_main + 253
12 llc             0x0000000000535829
Stack dump:
0.    Program arguments: llc make_trampoline.ll 
1.    Running pass 'Function Pass Manager' on module 'make_trampoline.ll'.
2.    Running pass 'Module Verifier' on function '@make_trampoline'
Aborted
=====

Commenting out this assert in the verifier shows it is currently backed up by
one in the SelectionDAGBuilder (by way of cast<Function>):
=====
$ llc make_trampoline.ll
llc: /home/urxae/opt/llvm/trunk/include/llvm/Support/Casting.h:202: typename
llvm::cast_retty<To, From>::ret_type llvm::cast(const Y&) [with X =
llvm::Function, Y = llvm::Value*]: Assertion `isa<X>(Val) && "cast<Ty>()
argument of incompatible type!"' failed.
0  llc             0x0000000000da928f
1  llc             0x0000000000dab502
2  libpthread.so.0 0x00007f771ea9d8f0
3  libc.so.6       0x00007f771dd8ca75 gsignal + 53
4  libc.so.6       0x00007f771dd905c0 abort + 384
5  libc.so.6       0x00007f771dd85941 __assert_fail + 241
6  llc             0x0000000000917abc
llvm::SelectionDAGBuilder::visitIntrinsicCall(llvm::CallInst const&, unsigned
int) + 17372
7  llc             0x0000000000917fae
llvm::SelectionDAGBuilder::visitCall(llvm::CallInst const&) + 654
8  llc             0x00000000008ffb2a llvm::SelectionDAGBuilder::visit(unsigned
int, llvm::User const&) + 394
9  llc             0x0000000000925d0d
llvm::SelectionDAGBuilder::visit(llvm::Instruction const&) + 45
10 llc             0x0000000000933aa0
llvm::SelectionDAGISel::SelectBasicBlock(llvm::ilist_iterator<llvm::Instruction
const>, llvm::ilist_iterator<llvm::Instruction const>, bool&) + 160
11 llc             0x00000000009340f4
llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) + 1460
12 llc             0x0000000000934da6
llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) + 486
13 llc             0x0000000000cfb6cd
llvm::FPPassManager::runOnFunction(llvm::Function&) + 557
14 llc             0x0000000000cfb7cb
llvm::FPPassManager::runOnModule(llvm::Module&) + 75
15 llc             0x0000000000cfb257
llvm::MPPassManager::runOnModule(llvm::Module&) + 503
16 llc             0x0000000000cfb3d7 llvm::PassManagerImpl::run(llvm::Module&)
+ 167
17 llc             0x000000000053744d main + 4109
18 libc.so.6       0x00007f771dd77c4d __libc_start_main + 253
19 llc             0x0000000000535829
Stack dump:
0.    Program arguments: llc make_trampoline.ll 
1.    Running pass 'Function Pass Manager' on module 'make_trampoline.ll'.
2.    Running pass 'X86 DAG->DAG Instruction Selection' on function
'@make_trampoline'
Aborted
=====

Is there any reason for this?
As far as I can tell, there's no reason llvm.init.trampoline shouldn't be able
to work for function pointers; the nest arg is given a specially-reserved
register in the callling convention (at least on X86 and X86-64, I didn't check
the other backends) so it's not like the argument list actually has to be
rewritten by it. That means it should be able to just store some static code
and the pointers to the memory provided, right?

(At the very least, this should be more clearly documented in LangRef.html if
this was intentional; it does currently say "The func argument must hold a
function bitcast to an i8*.", but that could be interpreted to mean
"indirection" by way of function arguments, phi nodes, etc. is allowed)

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