[Bug gold/19577] Gold failed to build with GCC 5.3

[ccoutant at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=19577

--- Comment #7 from Cary Coutant <ccoutant at gmail dot com> ---
> /export/gnu/import/git/sources/binutils-gdb/gold/reloc.h:1009:37: error:
> integer overflow in expression [-Werror=overflow]
>      int32_t max = (1 << (bits - 1)) - 1;
>                                      ^

> /export/gnu/import/git/sources/binutils-gdb/gold/reloc.h:1023:46: error: left
> shift count >= width of type [-Werror=shift-count-overflow]
>      uint32_t max = static_cast<uint32_t>((1U << bits) - 1);

Hmmm, in both of these cases, I'd have expected the compiler to do
enough constant propagation to see that the code it's complaining
about is dead when bits == 32.

Here's a patch that I think makes the code both clearer and more
compiler-proof.

I'm having trouble doing a full build with the trunk compiler, but I
did do some testing on the side to try to make sure this code compiles
clean and correctly. (I'm running stock Ubuntu on a VM, with GCC 4.8.2
installed. And no multilib either.)

-cary


2016-02-06  Cary Coutant  <address@hidden>

gold/
        * reloc.h (Limits): New class.
        (Bits::has_overflow32): Use min/max values from Limits.
        (Bits::has_unsigned_overflow32): Likewise.
        (Bits::has_signed_unsigned_overflow32): Likewise.
        (Bits::has_overflow): Likewise.
        (Bits::has_unsigned_overflow): Likewise.
        (Bits::has_signed_unsigned_overflow64): Likewise.

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