[llvm-dev] SDNode type UNDEF in new llvm-backend

[Markus Weinhardt via llvm-dev]

Hello!

I'm new to llvm and have the following problem trying to implement a new
backend, based on the LEG-backend by Fraser Cormack.

I used the standard clang command (under Ubuntu) to generate main.bc
from the following tiny program:

main.c:
void main() {
  volatile int a, b, c;
  c = a - b;
}

I then used the following command:
llc -march=lacore -debug -print-after-all main.bc -o main.s

The program terminated with an assertion violation, see output below.
The UNDEF node (t3) apparently causes the problem. But, according to my
understanding, this node is already generated in the IR->DAG translation
and already exisiting in the initial selection DAG (in the load and
store commands). Therefore, it is probably not related to my own,
error-prone target implementation. That makes the problem even harder to
understand. I could not find out where the UNDEF SDNode is generated.

Thank you in advance for any hints!

Best regards,
Markus

---------------------------------------------------------------------
...

*** IR Dump After Module Verifier ***
; Function Attrs: nounwind uwtable
define void @main() #0 {
  %a = alloca i32, align 4
  %b = alloca i32, align 4
  %c = alloca i32, align 4
  %1 = load volatile i32, i32* %a, align 4
  %2 = load volatile i32, i32* %b, align 4
  %3 = sub nsw i32 %1, %2
  store volatile i32 %3, i32* %c, align 4
  ret void
}
---- Branch Probability Info : main ----

Computing probabilities for

=== main
Initial selection DAG: BB#0 'main:'
SelectionDAG has 11 nodes:
  t2: i32 = Constant<0>
    t0: ch = EntryToken
  t4: i32,ch = load<Volatile LD4[%a]> t0, FrameIndex:i32<0>, undef:i32
  t6: i32,ch = load<Volatile LD4[%b]> t4:1, FrameIndex:i32<1>, undef:i32
      t7: i32 = sub t4, t6
    t9: ch = store<Volatile ST4[%c]> t6:1, t7, FrameIndex:i32<2>, undef:i32
  t10: ch = RetFlag t9

...

*** Final schedule ***
SU(2): t3: i32 = undef

SU(4): t4: i32,ch = load<Volatile LD4[%a]> t0, FrameIndex:i32<0>, undef:i32

SU(5): t6: i32,ch = load<Volatile LD4[%b]> t4:1, FrameIndex:i32<1>,
undef:i32

SU(3): t7: i32 = sub t4, t6

SU(1): t9: ch = store<Volatile ST4[%c]> t6:1, t7, FrameIndex:i32<2>,
undef:i32

SU(0): t10: ch = RetFlag t9


t3: i32 = undef
This target-independent node should have been selected!
UNREACHABLE executed at
/home/markus/llvm_inst/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp:889!



-- 
Prof. Dr.-Ing. Markus Weinhardt -  Hochschule Osnabrück
Visiting Researcher at www.inesc-id.pt -ESDA, Lisbon/PT
mweinhardt at computer.org  -  Tel.nr. +49-(0)541-969 3445
Postf. 1940, 49009 Osnabrück (Artilleriestr. 46, SB223)
http://www.ecs.hs-osnabrueck.de/weinhardt.html