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.
