[LLVMbugs] [Bug 16332] New: Vectorize loops with multiple exits

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Fri Jun 14 13:27:05 PDT 2013


            Bug ID: 16332
           Summary: Vectorize loops with multiple exits
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: benny.kra at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

ICC can vectorize this loop, and this kind of loop is not uncommon:

int foo(int max, int *arr) {
  int i;
  for (i = 0; i < max; i++)
    if (arr[i] != 0) break;
  return i;

Looks simple but is quite impressive. I'm not sure how it decides that
widenening the load in the loop is legal.

The kernel becomes a pcmpeqd + movmskps + testl, with a bsf on the exit to get
the right return value.

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