cba4accda0
In the following loop the dependence distance is 2 and can only be
vectorized if the vector length is no larger than this.
void foo(int *a, int *b, int N) {
#pragma clang loop vectorize(enable) vectorize_width(4)
for (int i=0; i<N; ++i) {
a[i + 2] = a[i] + b[i];
}
}
However, when specifying a VF of 4 via a loop hint this loop is
vectorized. According to [1][2], loop hints are ignored if the
optimization is not safe to apply.
This patch introduces a check to bail of vectorization if the user
specified VF is greater than the maximum feasible VF, unless explicitly
forced with '-force-vector-width=X'.
[1] https://llvm.org/docs/LangRef.html#llvm-loop-vectorize-and-llvm-loop-interleave
[2] https://clang.llvm.org/docs/LanguageExtensions.html#extensions-for-loop-hint-optimizations
Reviewed By: sdesmalen, fhahn, Meinersbur
Differential Revision: https://reviews.llvm.org/D90687
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| .. | ||
| Oz-and-forced-vectorize.ll | ||
| aarch64-predication.ll | ||
| aarch64-unroll.ll | ||
| arbitrary-induction-step.ll | ||
| arm64-unroll.ll | ||
| backedge-overflow.ll | ||
| deterministic-type-shrinkage.ll | ||
| extractvalue-no-scalarization-required.ll | ||
| gather-cost.ll | ||
| induction-trunc.ll | ||
| interleaved-vs-scalar.ll | ||
| interleaved_cost.ll | ||
| lit.local.cfg | ||
| loop-vectorization-factors.ll | ||
| loopvectorize_pr33804_double.ll | ||
| max-vf-for-interleaved.ll | ||
| no_vector_instructions.ll | ||
| nontemporal-load-store.ll | ||
| outer_loop_test1_no_explicit_vect_width.ll | ||
| pr31900.ll | ||
| pr33053.ll | ||
| pr36032.ll | ||
| pr46950-load-cast-context-crash.ll | ||
| predication_costs.ll | ||
| reduction-small-size.ll | ||
| sdiv-pow2.ll | ||
| select-costs.ll | ||
| smallest-and-widest-types.ll | ||
| sve-scalable-load-in-loop.ll | ||
| type-shrinkage-insertelt.ll | ||
| unsafe-vf-hint-remark.ll | ||