[Bug c++/27336] New: "this" pointer is not assumed to be not null

[guillaume dot melquiond at ens-lyon dot fr]

I noticed that GCC tends to litter the assembly code with null checks and jumps
(especially for dynamic casts) even when the pointer cannot be null. This is
especially true for "this": unless I am mistaken, calling a nonstatic member
with "this" not pointing to an object of the correct type (or a derived type)
is undefined behavior. So GCC should assume it is not null. I tried the
following testcase with 3.4.6, 4.0.3, and 4.1.0; GCC was never able to optimize
the return value to "true" when compiling with -O3.

struct A { bool g(); };
bool A::g() { return this; }


-- 
           Summary: "this" pointer is not assumed to be not null
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: guillaume dot melquiond at ens-lyon dot fr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27336