[Sparc] Code generator asserts on alloca of zero size type

[llvmbot]

Bugzilla Link	299
Resolution	FIXED
Resolved on	Feb 22, 2010 12:43
Version	1.0
OS	All
Attachments	Code to reproduce problem
Reporter	LLVM Bugzilla Contributor

Extended Description

The llc program on Solaris generates the following assertion on the attached input:

Assertion failed: tsize > 0 && "Illegal (zero) type size for alloca", file
/home/vadve/criswell/rel12/llvm/lib/Target/SparcV9/SparcV9InstrSelection.cpp,
line 1159
Abort

The Linux/x86 code generator accepts the input.

[llvmbot]

assigned to @lattner

[lattner]

That alloca seems pretty pointless. Are all of the failures on C++ programs?
If so, I wouldn't worry about this at all for the release. The sparc backend
has never worked well with the C++ standard library, and now does not seem like
the time to fix it...

-Chris

[lattner]

I've verified that this is perfectly correct code being generated and optimized
by the C++ front-end. It basically comes from something like this:

unsigned Amt = blah ? x : 0;
X = builtin_alloca(Amt);

The alloca gets tail duplicated into the two arms of the conditional, becoming
'alloca 0' in the false arm.

I'll try to fix this in the sparc backend. Wish me luck :)

-Chris

[lattner]

Fixed, patch here:
http://mail.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20040315/013269.html

I don't know if the code really will break on a zero sized alloca, so I just had
it pretend to be a unit sized alloca instead. This seems to fix the problem :)

-Chris