[llvm-bugs] [Bug 51427] New: Missed loop vectorization (fmul src[idx[i]], constant)

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=51427

            Bug ID: 51427
           Summary: Missed loop vectorization (fmul src[idx[i]], constant)
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: david.bolvansky at gmail.com
                CC: llvm-bugs at lists.llvm.org

#include <stdint.h>

void mulPi(double * const __restrict__ dst,
          double const * const __restrict__ src,
          uint32_t const * const __restrict__ idx,
          uint32_t const begin,
          uint32_t const end)
{
  for (uint32_t i = begin; i < end; ++i)
    dst[i] = 3.141 * src[idx[i]];
}


GCC and ICC vectorizes this code just fine.


LLVM:
remark: the cost-model indicates that vectorization is not beneficial
[-Rpass-missed=loop-vectorize]

remark: the cost-model indicates that interleaving is not beneficial
[-Rpass-missed=loop-vectorize]


https://godbolt.org/z/4j44KKT3c

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