[Bug c++/100884] New: Comparing unsigned 32 bit integer values generates 64 bit compare instructions when optimized

["mfarazma.ext at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100884

            Bug ID: 100884
           Summary: Comparing unsigned 32 bit integer values generates 64
                    bit compare instructions when optimized
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mfarazma.ext at gmail dot com
  Target Milestone: ---

**0.c**
```
#include <iostream>

uint32_t codegen();

int main(){
 uint32_t expected = (codegen()) != 0 ? -1 : -2;
 bool check_eq = expected == codegen();
 if (!(check_eq)){
   std::cout << "Check failed" << std::endl;
 }
 return 0;
}
```

**1.cc**
```
#include <iostream>

uint32_t codegen(){
 volatile int64_t a = -1; 
 return a;
}
```

Compile it with optimization enabled:
g++ -O3 0.cc 1.cc

Checking the generate code shows this instruction is generated for ` if
(!(check_eq)){...}`:
```
cmpd    r31,r3 
```

Compiling the same code with gcc version 8.4.0 emits this instead which is
correct:
```
cmpw    cr7,r3,r31
```

This issue is causing failures as the returned value from `codegen()` may not
have its upper 32 bits cleared and using `cmpd` on it will create the wrong
output.