Aligned argument crashes x86_64 backend when targeting Linux

[991901f3-cc14-4404-b340-165691b62a58]

Bugzilla Link	21088
Version	unspecified
OS	All
CC	@echristo,@hfinkel

Extended Description

consider: cat ~/t.cpp

struct __attribute__((aligned(32))) A {
  long x, y;
};
long f(struct A a) { return a.y; }

~/llvm/Debug+Asserts/bin/clang -cc1 -x c -triple x86_64-pc-linux ~/t.cpp -S -o -

clang: ~/llvm/src/lib/CodeGen/MachineFunction.cpp:499: void llvm::MachineFrameInfo::ensureMaxAlignment(unsigned int): Assertion `Align <= getFrameLowering()->getStackAlignment() && "For targets without stack realignment, Align is out of limit!"' failed.
0  clang           0x00000000021aa8db llvm::sys::PrintStackTrace(_IO_FILE*) + 38
1  clang           0x00000000021aab58
2  clang           0x00000000021aa457
3  libpthread.so.0 0x00007f3326b60340
4  libc.so.6       0x00007f3325f9dbb9 gsignal + 57
5  libc.so.6       0x00007f3325fa0fc8 abort + 328
6  libc.so.6       0x00007f3325f96a76
7  libc.so.6       0x00007f3325f96b22
8  clang           0x0000000001b51380 llvm::MachineFrameInfo::ensureMaxAlignment(unsigned int) + 132
9  clang           0x0000000001abc92a llvm::CCState::HandleByVal(unsigned int, llvm::MVT, llvm::MVT, llvm::CCValAssign::LocInfo, int, int, llvm::ISD::ArgFlagsTy) + 116
10 clang           0x00000000017e7519
11 clang           0x00000000017e7422
12 clang           0x00000000017e509a
13 clang           0x0000000001abcae8 llvm::CCState::AnalyzeFormalArguments(llvm::SmallVectorImpl<llvm::ISD::InputArg> const&, bool (*)(unsigned int, llvm::MVT, llvm::MVT, llvm::CCValAssign::LocInfo, llvm::ISD::ArgFlagsTy, llvm::CCState&)) + 128
14 clang           0x00000000017eeac1 llvm::X86TargetLowering::LowerFormalArguments(llvm::SDValue, unsigned int, bool, llvm::SmallVectorImpl<llvm::ISD::InputArg> const&, llvm::SDLoc, llvm::SelectionDAG&, llvm::SmallVectorImpl<llvm::SDValue>&) const + 635
15 clang           0x0000000002605212 llvm::SelectionDAGISel::LowerArguments(llvm::Function const&) + 2604
16 clang           0x0000000002621bfb llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) + 979
17 clang           0x000000000261e9d5 llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) + 1091
18 clang           0x00000000017c5190
19 clang           0x0000000001b5993d llvm::MachineFunctionPass::runOnFunction(llvm::Function&) + 95
20 clang           0x0000000001e22cdc llvm::FPPassManager::runOnFunction(llvm::Function&) + 290
21 clang           0x0000000001e22e4c llvm::FPPassManager::runOnModule(llvm::Module&) + 84
22 clang           0x0000000001e2316a
23 clang           0x0000000001e2380e llvm::legacy::PassManagerImpl::run(llvm::Module&) + 244
24 clang           0x0000000001e23a2d llvm::legacy::PassManager::run(llvm::Module&) + 39
25 clang           0x00000000026d5791
26 clang           0x00000000026d5860 clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::CodeGenOptions const&, clang::TargetOptions const&, clang::LangOptions const&, llvm::StringRef, llvm::Module*, clang::BackendAction, llvm::raw_ostream*) + 127
27 clang           0x00000000026be04d
28 clang           0x0000000003061ce2 clang::ParseAST(clang::Sema&, bool, bool) + 776
29 clang           0x000000000238f8d2 clang::ASTFrontendAction::ExecuteAction() + 322
30 clang           0x00000000026c032d clang::CodeGenAction::ExecuteAction() + 1467
31 clang           0x000000000238f3ad clang::FrontendAction::Execute() + 139
32 clang           0x000000000235a470 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) + 770
33 clang           0x000000000249855b clang::ExecuteCompilerInvocation(clang::CompilerInstance*) + 993
34 clang           0x000000000110858e cc1_main(llvm::ArrayRef<char const*>, char const*, void*) + 770
35 clang           0x0000000001101534
36 clang           0x0000000001101ae0 main + 1015
37 libc.so.6       0x00007f3325f88ec5 __libc_start_main + 245
38 clang           0x00000000010fe789
Stack dump:
0.      Program arguments: ~/llvm/Debug+Asserts/bin/clang -cc1 -x c -triple x86_64-pc-linux t.cpp -S -o - 
1.      <eof> parser at end of file
2.      Code generation
3.      Running pass 'Function Pass Manager' on module 't.cpp'.
4.      Running pass 'X86 DAG->DAG Instruction Selection' on function '@f'

[llvmbot]

I suspect the assert() is misleading a bit. Dynamic stack realignment can't do anything to help with function arguments, just local variables.

[echristo]

Weird, linux is supposed to support dynamic realignment, otherwise how do we handle avx stuff on the stack? Adding Jim because he's been in this area the most.

[Endilll]

Can't reproduce using Clang 3.5 and 3.6 with assertions enabled: https://godbolt.org/z/96qs3zMq3

[llvmbot]

@llvm/issue-subscribers-c

[llvmbot]

@llvm/issue-subscribers-backend-x86