On Thu, Dec 22, 2011 at 2:59 AM, Bin Cheng <bin.ch...@arm.com> wrote: > Hi, > > This patch fixes the bug PR43491, which exists at least on > arm-none-eabi/mips-elf > targets. > > The cause is ssa-pre eliminates global register variable when it is the RHS > of > single assign statment, while following passes do not handle the > const/register > attributes of the variable. > > This patch skips the elimination of global register variable when it is the > RHS > of a single assignment in SSA-PRE pass. > > By doing this, > > 0) gcc won't generate the redundant move instruction as reported in the bug. > 1) normal redundancy elimination on global registers will not be hurt, > since sccvn and pre has already detected the true elimination chances > and they will be eliminated afterward in function eliminate. > 2) the inserted statements(including PHIs) for global register variables > will not be marked as NECESSARY in function eliminate and will be > deleted in remove_dead_inserted_code. So no redundant insertions will be > generated in PRE pass. > > Some discussion can be found at: > http://gcc.gnu.org/ml/gcc/2011-12/msg00000.html > > The patch is tested on x86 and arm-none-eabi, no failure introduced. > > Is it OK?
Ok. Thanks, Richard. > Thanks > > gcc/ChangeLog: > 2011-12-21 Bin Cheng <bin.ch...@arm.com> > Richard Guenther <rguent...@suse.de> > > PR tree-optimization/43491 > * tree-ssa-pre.c (eliminate): Don't replace global register variable > when > it is the RHS of a single assign. > > gcc/testsuite/ChangeLog: > 2011-12-21 Bin Cheng <bin.ch...@arm.com> > > PR tree-optimization/43491 > * gcc.dg/tree-ssa/pr43491.c: New test.
