error: ran out of registers during register allocation

[Quuxplusone]

Bugzilla Link	PR11395
Status	NEW
Importance	P enhancement
Reported by	Kostya Serebryany (kcc@google.com)
Reported on	2011-11-17 11:57:42 -0800
Last modified on	2012-01-11 15:28:43 -0800
Version	trunk
Hardware	PC Linux
CC	echristo@gmail.com, efriedma@quicinc.com, llvm-bugs@lists.llvm.org, stoklund@2pi.dk
Fixed by commit(s)
Attachments	z.o.ll (23682 bytes, application/octet-stream) y.ll (1110 bytes, application/octet-stream)
Blocks
Blocked by
See also

Reproducer:
% ./Release+Asserts/bin/llc  z.o.ll
error: ran out of registers during register allocation

Reduced from ffmpeg sources (with inline assembly) building with
AddressSanitizer for x86_32

Observed on r144798

[Quuxplusone]

Attachment is missing.

[Quuxplusone]

This is another case where "m" constraints referring to alloca objects get their own register instead of using the stack/frame pointer.

[Quuxplusone]

Attached z.o.ll (23682 bytes, application/octet-stream): .ll file

[Quuxplusone]

Attached y.ll (1110 bytes, application/octet-stream): further reduced testcase

[Quuxplusone]

(In reply to comment #3)
> This is another case where "m" constraints referring to alloca objects get
> their own register instead of using the stack/frame pointer.

Err, no, I'm pretty sure the issue is that there's an inline asm which requires
7 registers in a function using stack realignment (which means there are only 6
registers available).

[Quuxplusone]

> Err, no, I'm pretty sure the issue is that there's an inline asm which
requires
> 7 registers in a function using stack realignment (which means there are only
6
> registers available).

Interesting, bugpoint changes it from one to the other.

[Quuxplusone]

r144962 added a workaround for AddressSanitizer.

[Quuxplusone]

I had to extend the workaround (r147953).
Before that revision codegen fails even if -faddress-sanitizer does not cause
stack realignment.

% cat bug11395.c
void foo_386(int *a, const int *b,
             unsigned int f, int d,
             int h, int *c, int *e, int *g)
{
  __asm__ volatile(
      "int3"
      : "+r"(a),
      "+r"(b),
      "+r"(c),
      "+m"(h)
      : "m"( d), "m"(g),
      "m"(e) , "m"(f)
      : "eax", "edx", "esi", "ecx"
      );
}

clang  -m32  -O1 -c -faddress-sanitizer    -fno-omit-frame-pointer bug11395.c
bug11395.c:6:7: error: ran out of registers during register allocation
      "int3"
      ^
1 error generated.

[Quuxplusone]

(In reply to comment #8)
> clang  -m32  -O1 -c -faddress-sanitizer    -fno-omit-frame-pointer bug11395.c
> bug11395.c:6:7: error: ran out of registers during register allocation
>       "int3"
>       ^

The given example doesn't compile even without -faddress-sanitizer: it requires
7 registers, and there are only 6 registers available.

[Quuxplusone]

Hm. It compiles fine for me w/o -faddress-sanitizer.

[Quuxplusone]

But it indeed fails with -mstackrealign:

clang -m32 bug11395.c -c -mstackrealign
bug11395.c:6:7: error: ran out of registers during register allocation

[Quuxplusone]

That's because the realignment will need another register.