[PATCH] D65463: [WebAssembly] Fix conflict between ret legalization and sjlj

[Keno Fischer via Phabricator via llvm-commits]

loladiro created this revision.
loladiro added reviewers: sbc100, kripken.
Herald added subscribers: llvm-commits, s.egerton, Jim, jsji, jocewei, PkmX, the_o, brucehoult, MartinMosbeck, rogfer01, atanasyan, edward-jones, zzheng, MaskRay, jrtc27, niosHD, sabuasal, apazos, sunfish, simoncook, johnrusso, rbar, asb, kbarton, aheejin, hiraditya, jgravelle-google, javed.absar, nhaehnle, jvesely, nemanjai, sdardis, dylanmckay, dschuff, arsenm.
Herald added a project: LLVM.

When the WebAssembly backend encounters a return type that doesn't
fit within i32, SelectionDAG performs sret demotion, adding an
additional argument to the start of the function that contains
a pointer to an sret buffer to use instead. However, this conflicts
with the emscripten sjlj lowering pass. There we translate calls like:

  	call {i32, i32} @foo()

into (in pseudo-llvm

  	%addr = @foo
  	call {i32, i32} @__invoke_{i32,i32}(%addr)

i.e. we perform an indirect call through an extra function.
However, the sret transform now transforms this into
the equivalent of

  %addr = @foo
  %sret = alloca {i32, i32}
  call {i32, i32} @__invoke_{i32,i32}(%sret, %addr)

(while simultaneously translation the implementation of @foo as well).
Unfortunately, this doesn't work out. The __invoke_ ABI expected
the function address to be the first argument, causing crashes.

There is several possible ways to fix this:

1. Implementing the sret rewrite at the IR level as well and performing it as part of lowering to __invoke
2. Fixing the wasm backend to recognize that __invoke has a special ABI
3. A change to the binaryen/emscripten ABI to recognize this situation

This revision implements the middle option, teaching the backend to
treat __invoke_ functions specially in sret lowering. This is achieved
by

1. Introducing a new CallingConv ID for invoke functions
2. Adding a hook to CanLowerReturn to override which argument is used for the sret pointer.

This revision isn't quite complete and definitely needs a test
(and I'm considering dropping the hook in 2) in favor of just
swizzeling the arguments in lowerCall), but I have verified
that it indeed fixes the observed crashes, so it should be
sufficient to discuss whether this is the correct approach.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D65463

Files:
  llvm/include/llvm/CodeGen/TargetLowering.h
  llvm/include/llvm/IR/CallingConv.h
  llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
  llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
  llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
  llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
  llvm/lib/Target/AArch64/AArch64ISelLowering.h
  llvm/lib/Target/AMDGPU/SIISelLowering.cpp
  llvm/lib/Target/AMDGPU/SIISelLowering.h
  llvm/lib/Target/ARC/ARCISelLowering.cpp
  llvm/lib/Target/ARC/ARCISelLowering.h
  llvm/lib/Target/ARM/ARMISelLowering.cpp
  llvm/lib/Target/ARM/ARMISelLowering.h
  llvm/lib/Target/AVR/AVRISelLowering.cpp
  llvm/lib/Target/AVR/AVRISelLowering.h
  llvm/lib/Target/Hexagon/HexagonISelLowering.cpp
  llvm/lib/Target/Hexagon/HexagonISelLowering.h
  llvm/lib/Target/MSP430/MSP430ISelLowering.cpp
  llvm/lib/Target/MSP430/MSP430ISelLowering.h
  llvm/lib/Target/Mips/MipsISelLowering.cpp
  llvm/lib/Target/Mips/MipsISelLowering.h
  llvm/lib/Target/PowerPC/PPCISelLowering.cpp
  llvm/lib/Target/PowerPC/PPCISelLowering.h
  llvm/lib/Target/RISCV/RISCVISelLowering.cpp
  llvm/lib/Target/RISCV/RISCVISelLowering.h
  llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
  llvm/lib/Target/SystemZ/SystemZISelLowering.h
  llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
  llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.h
  llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/lib/Target/X86/X86ISelLowering.h
  llvm/lib/Target/XCore/XCoreISelLowering.cpp
  llvm/lib/Target/XCore/XCoreISelLowering.h

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D65463.212390.patch
Type: text/x-patch
Size: 25771 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20190730/f0a7c2c6/attachment-0001.bin>