On 12/11/2017 07:18 AM, James Greenhalgh wrote: > > Hi, > > In simplify_set we try transforming the paradoxical subreg expression: > > (set FOO (subreg:M (mem:N BAR) 0)) > > in to: > > (set FOO (zero_extend:M (mem:N BAR))) > > However, this code does not consider the case where M is a vector > mode, allowing it to construct (for example): > > (zero_extend:V4SI (mem:SI)) > > This would clearly have the wrong semantics, but fortunately we fail long > before then in expand_compound_operation. As we really don't want a vector > zero_extend of a scalar value. > > We need to explicitly reject vector modes from this transformation. > > This fixes a failure I'm seeing on a branch in which I'm trying to > tackle some performance regressions, so I have no live testcase for > this, but it is wrong by observation. > > Tested on aarch64-none-elf and bootstrapped on aarch64-none-linux-gnu with > no issues. > > OK? > > Thanks, > James > > --- > 2017-12-11 James Greenhalgh <james.greenha...@arm.com> > > * combine.c (simplify_set): Do not transform subregs to zero_extends > if the destination mode is a vector mode. > OK. Ideally you'd have a test for the testsuite as well, but I won't stress without it :-)
jeff
