[llvm-bugs] [Bug 44679] New: Missed constant propagation optimization in simple while loop

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=44679

            Bug ID: 44679
           Summary: Missed constant propagation optimization in simple
                    while loop
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: klrehm123 at gmail.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

//////////////////
int foo(int a) {
    int num = 0;
    int n = 1;
    while (true) {
        if (n == 1) {
            num++;
            n = 2;
        } else if(n == 2) {
            num += 2;
            n = 3;
        } 
        else if(n == 3) {
            return num;
        }
    }
}
//////////////////
Optimized away in GCC, but not with LLVM trunk.
Interestingly, copying the loop body twice does get optimized:

//////////////////
int bar(int a) {
    int num = 0;
    int n = 1;
    while (true) {
        if (n == 1) {
            num++;
            n = 2;
        } else if(n == 2) {
            num += 2;
            n = 3;
        } 
        else if(n == 3) {
            return num;
        }

        if (n == 1) {
            num++;
            n = 2;
        } else if(n == 2) {
            num += 2;
            n = 3;
        } 
        else if(n == 3) {
            return num;
        }
    }
}
//////////////////

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