[llvm-bugs] [Bug 38853] New: Not vectorized trivial case since LAA (SCEV) fails to figure out exit counts

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38853

            Bug ID: 38853
           Summary: Not vectorized trivial case since LAA (SCEV) fails to
                    figure out exit counts
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: balarishi.bhogadi at amd.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 20848
  --> https://bugs.llvm.org/attachment.cgi?id=20848&action=edit
Testcase to reproduce the issue

BUG DETAILS:

LLVM is not able to vectorize below trivial case:

----------------
extern int len;
extern int *ptr_x, *ptr_y, *ptr_z;
void foo()
{
   for (int i = 0; i < len; i++)
      ptr_x[i] = ptr_y[i] * ptr_z[i];
}
----------------

The reason for this is LAA (SCEV) is not able to figure out the exit counts.

LV: Can't vectorize due to memory conflicts
LAA: SCEV could not compute the loop exit count.

This test looks trivial and LAA is not able to figure out the loop exit.

This issue is not seen when arrays are used instead of pointers.

==========================================
STEPS to REPRODUCE:

- Download the attached vect.c file
- Run the below command:
   clang -O3 -S -emit-llvm -o vect.ll  vect.c

==========================================

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