https://bugs.llvm.org/show_bug.cgi?id=35520
Bug ID: 35520
Summary: Wrong codegen for i1 vector truncating stores
Product: libraries
Version: trunk
Hardware: Other
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Common Code Generator Code
Assignee: unassignedb...@nondot.org
Reporter: uweig...@de.ibm.com
CC: llvm-b...@justinbogner.com, llvm-bugs@lists.llvm.org,
matthew.arsena...@amd.com, pauls...@linux.vnet.ibm.com
The following simple test case generates completely broken code on SystemZ (run
with -mcpu=z13 to enable the vector ISA):
define i16 @test(<16 x i1> %src)
{
%res = bitcast <16 x i1> %src to i16
ret i16 %res
}
What happens is that in the ABI, the <16 x i1> is passed as <16 x i8>, so the
code would need to truncate to a real 16-bit vector, and reinterpret the result
as i16. For some reason, the code generator attempts to implement this as a
truncating store of a <16 x i8> in register to a <16 x i1> in memory, and then
loads that memory location as i16.
So far still OK, but the truncating store generates completely broken code: it
simply repeatedly stores all 16 bytes of the source vector to the same byte in
memory. Looking for the code that does this, I found this in
VectorLegalizer::ExpandStore (added by arsenm):
// FIXME: This is completely broken and inconsistent with ExpandLoad
// handling.
// For sub-byte element sizes, this ends up with 0 stride between elements,
// so the same element just gets re-written to the same location. There
seem
// to be tests explicitly testing for this broken behavior though. tests
// for this broken behavior.
which in fact matches exactly what I'm seeing.
What's going on here? Does this not happen on other platforms? Should I be
doing something different in the back-end, or should we try to fix this common
code issue after all? Any suggestions welcome ...
--
You are receiving this mail because:
You are on the CC list for the bug._______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
