[LLVMbugs] [Bug 194] NEW: [indvars] Induction variable canonicalization always makes 32-bit indvars

[bugzilla-daemon at zion.cs.uiuc.edu]

http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=194

           Summary: [indvars] Induction variable canonicalization always
                    makes 32-bit indvars
           Product: libraries
           Version: 1.0
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Scalar Optimizations
        AssignedTo: sabre at nondot.org
        ReportedBy: sabre at nondot.org


The induction variable canonicalization pass inserts new canonical induction
variables if a loop is lacking one, but it always chooses to insert a 32-bit
induction variable.  This can turn legal loops into infinite loops, such as this
one:

---
long long V;
int main() {
  long long X;
  for (X = 1; X < (1ULL << 33); ++X)
    V = X;
  printf("%lld\n", V);    // erroneously not reached
}
---

Though always introducing 64-bit induction variables would be acceptable, the
right approach is to insert a variable which is the largest of the existing
auxillary induction variables.

-Chris



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