[Bug middle-end/34282] New: Unnecessary load from volatile var

[ubizjak at gmail dot com]

This testcase:

int test (int a)
{
        volatile int z;

        z = a + 1;
        return z;
}

compiles into:

test:
        subl    $16, %esp       #,
        movl    20(%esp), %eax  # a, z.0
        addl    $1, %eax        #, z.0
        movl    %eax, 12(%esp)  # z.0, z
(1)     movl    12(%esp), %eax  # z, D.1178
        addl    $16, %esp       #,
        ret

IMO, there is no need for (1), since we already have correct value in %eax.
However, even when value lives in another register, we should load it into the
return register from the reg, not from mem location.


-- 
           Summary: Unnecessary load from volatile var
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ubizjak at gmail dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34282