[Bug rtl-optimization/56339] New: [4.8 Regression]: Suboptimal register allocation

[ubizjak at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56339



             Bug #: 56339

           Summary: [4.8 Regression]: Suboptimal register allocation

    Classification: Unclassified

           Product: gcc

           Version: 4.8.0

            Status: UNCONFIRMED

          Keywords: ra

          Severity: normal

          Priority: P3

         Component: rtl-optimization

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: ubiz...@gmail.com

                CC: vmaka...@gcc.gnu.org





Split out from PR55941.



The testcase from referred PR



--cut here--

typedef struct A { double a, b; } A;

double f(A x,double y){return x.a+y;}

--cut here--



compiles to (-O2):



f:

        addsd   %xmm0, %xmm2

        movapd  %xmm2, %xmm0

        ret



gcc-4.7 generates:



f:

        addsd   %xmm2, %xmm0

        ret



LRA does not take into account commutative operands here.