[Bug c/70378] New: [5.3] inconsistant warnings with -Wconversion for different types

[daniel.f.starke at freenet dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70378

            Bug ID: 70378
           Summary: [5.3] inconsistant warnings with -Wconversion for
                    different types
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: daniel.f.starke at freenet dot de
  Target Milestone: ---

Tested with GCC 4.4.3 and 5.3.0 whereas 5.3.0 was configured as
Configured with: ../../src/gcc-5.3.0/configure --host=x86_64-w64-mingw32
--enable-languages=c,c++ --enable-seh-exceptions --enable-threads=posix
--disable-nls --disable-shared --enable-static --enable-fully-dynamic-string
--enable-lto --enable-plugins --enable-libgomp --with-dwarf2
--disable-win32-registry --enable-version-specific-runtime-libs
--prefix=/mingw64-64 --with-sysroot=/mingw64-64 --target=x86_64-w64-mingw32
--enable-targets=all --enable-checking=release
--with-gmp=/usr/new-gcc/lib/gmp-5.0.5 --with-mpfr=/usr/new-gcc/lib/mpfr-2.4.2
--with-mpc=/usr/new-gcc/lib/mpc-0.9 --with-isl=/usr/new-gcc/lib/isl-0.12.2
--with-cloog=/usr/new-gcc/lib/cloog-0.18.3 --with-host-libstdcxx='-lstdc++
-lsupc++' --disable-cloog-version-check --enable-cloog-backend=isl

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

#define PARSE(Type) \
        do { \
                const char * a = str; \
                Type b = 0; \
                while (*a != 0) { \
                        b = (Type)((b * 10) + (Type)(*a) - '0'); \
                        a++; \
                } \
                printf(#Type " = %u\n", (unsigned int)b); \
        } while (0)

int main() {
        const char * str = "123";

        PARSE(int8_t);
        PARSE(int16_t);
        PARSE(int32_t);
        PARSE(int64_t);
        PARSE(uint8_t);
        PARSE(uint16_t);
        PARSE(uint32_t);
        PARSE(uint64_t);
        PARSE(unsigned int);
        PARSE(unsigned);

        return EXIT_SUCCESS;
}

This code only produces a warning for uint32_t when compiled with -Wconversion:
test.c:10:24: warning: conversion to 'uint32_t {aka unsigned int}' from 'char'
may change the sign of the result [-Wsign-conversion]
    b = (Type)((b * 10) + (Type)(*a) - '0'); \
                        ^
test.c:25:2: note: in expansion of macro 'PARSE'
  PARSE(uint32_t);

uint32_t was defined as:
typedef unsigned   uint32_t;