[PATCH] D79100: [LV] Emit new IR intrinsic llvm.get.active.mask for tail-folded loops

[Florian Hahn via Phabricator via llvm-commits]

fhahn added inline comments.


================
Comment at: llvm/lib/Transforms/Vectorize/VPlan.cpp:425
+
+    Instruction *Call = Builder.CreateIntrinsic(
+        Intrinsic::get_active_lane_mask, {PredTy, ScalarBTC->getType()},
----------------
IIUC we want the first lanes of both the BTC and the IV, right?

If that's the case, I think it would be more straight-forward to just request the specific lane when looking up the values, .e.g something like:

```
   // Get first lane of vector induction variable.
    Value *VIVE0 = State.get(getOperand(0), {Part, 0});
    // Get first lane of backedge-taken-count.
    Value *ScalarBTC = State.get(getOperand(1), {Part, 0});

    auto *Int1Ty = Type::getInt1Ty(Builder.getContext());
    auto *PredTy = VectorType::get(Int1Ty, State.VF);
    Instruction *Call = Builder.CreateIntrinsic(
        Intrinsic::get_active_lane_mask, {PredTy, ScalarBTC->getType()},
        {VIVE0, ScalarBTC}, nullptr, "active.lane.mask");

    State.set(this, Call, Part);
```

This should have the advantage of re-using some scalar values, if they have been requested already by other recipes.

(Note: this currently crashes unfortunately, as getting lanes for defs managed by VPTransformState does not work, but I put up D80787 to fix that)


================
Comment at: llvm/test/Transforms/LoopVectorize/ARM/tail-loop-folding.ll:81
 ; PREDFLAG:  vector.body:
-; PREDFLAG:  %wide.masked.load = call <4 x i32> @llvm.masked.load.v4i32.p0v4i32(
-; PREDFLAG:  %wide.masked.load1 = call <4 x i32> @llvm.masked.load.v4i32.p0v4i32(
+; PREDFLAG:  %[[INDUCTION:induction.*]] = add <4 x i64> %broadcast.splat, <i64 0, i64 1, i64 2, i64 3>
+; PREDFLAG:  %[[ELEM0:.*]] = extractelement <4 x i64> %[[INDUCTION]], i64 0
----------------
We should also have a test where the unroll-factor/interleave-count > 1 with `llvm.get.active.lane.mask` (unless that's not possible at the moment)


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  https://reviews.llvm.org/D79100/new/

https://reviews.llvm.org/D79100