ExpandStructRegs: Assertion `New->getType() == getType() && "replaceAllUses of value with new value of different type!"' failed.

[TimNN]

While working upgrading rust to LLVM 4.0 (rust-lang/rust#40123) I encountered some code being miss-compiled. I investigated this some more recently and found that llc actually produces an assertion when those are enabled.

Compile the following with debug assertions enabled using llc -O0 foo.ll to reproduce:

; ModuleID = 'bugpoint-reduced-simplified.bc'
source_filename = "bugpoint-output-7eb0c3b.bc"
target datalayout = "e-p:32:32-i64:64-v128:32:128-n32-S128"
target triple = "asmjs-unknown-emscripten"

%WrappedArray = type { [2 x i64] }

define fastcc void @_read_wrapped_array(%WrappedArray*) {
entry-block:
  %1 = load %WrappedArray, %WrappedArray* %0, align 8
  %2 = extractvalue %WrappedArray %1, 0
  %.elt = extractvalue [2 x i64] %2, 0
  ret void
}

Output:

llc: .../clang/fastcomp/src/lib/IR/Value.cpp:375: void llvm::Value::doRAUW(llvm::Value*, bool): Assertion `New->getType() == getType() && "replaceAllUses of value with new value of different type!"' failed.
Stack dump:
0.	Program arguments: llc -O0 bugp.1.ll
1.	Running pass 'Function Pass Manager' on module 'bugp.1.ll'.
2.	Running pass 'Expand out variables with struct types' on function '@_read_wrapped_array'

Backtrace from gdb:

#3  0x00007ffff6931c62 in __assert_fail () from /lib/x86_64-linux-gnu/libc.so.6

#4  0x0000555556a05b08 in llvm::Value::doRAUW (this=0x5555586971a8, New=0x555558693b18, NoMetadata=false)
    at .../src/lib/IR/Value.cpp:374

#5  0x0000555556a05c66 in llvm::Value::replaceAllUsesWith (this=0x5555586971a8, New=0x555558693b18)
    at .../src/lib/IR/Value.cpp:402

#6  0x0000555556f50d65 in ExpandExtractValue (EV=0x5555586971a8, ToErase=0x7fffffffd6d0)
    at .../src/lib/Target/JSBackend/NaCl/ExpandStructRegs.cpp:468

#7  0x0000555556f50efb in ExpandExtractValues (Func=..., Finalize=false)
    at .../src/lib/Target/JSBackend/NaCl/ExpandStructRegs.cpp:485

#8  0x0000555556f5145c in (anonymous namespace)::ExpandStructRegs::runOnFunction (this=0x5555586a47c0, Func=...)
    at .../src/lib/Target/JSBackend/NaCl/ExpandStructRegs.cpp:557

#9  0x0000555556994e30 in llvm::FPPassManager::runOnFunction (this=0x5555586a4880, F=...)
    at .../src/lib/IR/LegacyPassManager.cpp:1513

#10 0x0000555556994fc9 in llvm::FPPassManager::runOnModule (this=0x5555586a4880, M=...)
    at .../src/lib/IR/LegacyPassManager.cpp:1534

#11 0x0000555556995344 in (anonymous namespace)::MPPassManager::runOnModule (this=0x55555868fb60, M=...)
    at .../src/lib/IR/LegacyPassManager.cpp:1590

#12 0x0000555556995a5b in llvm::legacy::PassManagerImpl::run (this=0x5555586a0c70, M=...)
    at .../src/lib/IR/LegacyPassManager.cpp:1693

#13 0x0000555556995c53 in llvm::legacy::PassManager::run (this=0x7fffffffdb10, M=...)
    at .../src/lib/IR/LegacyPassManager.cpp:1724

#14 0x0000555555dc3a16 in compileModule (argv=0x7fffffffe238, Context=...) at .../src/tools/llc/llc.cpp:528

#15 0x0000555555dc2054 in main (argc=3, argv=0x7fffffffe238) at .../src/tools/llc/llc.cpp:285

[TimNN]

I've been debugging a bit, and essentially the problem is, that at some point the following two lines are produced:

%.field = load [2 x i64], [2 x i64]* %.index, align 8
%.elt = extractvalue [2 x i64] %.field, 0

And it then tries to replace elt by field, which obviously doesn't work since field is [2 x i64] and elt is i64.

Note that those two lines passed directly to llc don't produce an assertion, leading me to believe that at some point some other pass needs to be run on the function.

[TimNN]

I've found the problem and a fix, PR incoming.

[TimNN]

This has been fixed.