[llvm] [LV, VP]VP intrinsics support for the Loop Vectorizer (PR #76172)

[Alexey Bataev via llvm-commits]

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@@ -348,6 +348,44 @@ Value *VPInstruction::generateInstruction(VPTransformState &State,
     Value *Zero = ConstantInt::get(ScalarTC->getType(), 0);
     return Builder.CreateSelect(Cmp, Sub, Zero);
   }
+  case VPInstruction::ExplicitVectorLength: {
+    // Compute EVL
+    auto GetSetVL = [=](VPTransformState &State, Value *EVL) {
+      assert(EVL->getType()->isIntegerTy() &&
+             "Requested vector length should be an integer.");
+
+      // TODO: Add support for MaxSafeDist for correct loop emission.
+      Value *VFArg = State.Builder.getInt32(State.VF.getKnownMinValue());
+
+      Value *GVL = State.Builder.CreateIntrinsic(
+          State.Builder.getInt32Ty(), Intrinsic::experimental_get_vector_length,
+          {EVL, VFArg, State.Builder.getTrue()});
+      return GVL;
+    };
+    // TODO: Restructure this code with an explicit remainder loop, vsetvli can
+    // be outside of the main loop.
+    assert(State.UF == 1 &&
+           "No unrolling expected for predicated vectorization.");
+    // Compute VTC - IV as the EVL(requested vector length).
+    Value *Index = State.get(getOperand(0), 0);
+    Value *TripCount = State.get(getOperand(1), VPIteration(0, 0));
+    Value *EVL = State.Builder.CreateSub(TripCount, Index);
+    Value *SetVL = GetSetVL(State, EVL);
+    State.EVL = this;
+    return SetVL;
+  }
+  case VPInstruction::ExplicitVectorLengthIVIncrement: {
+    assert(State.UF == 1 && Part == 0 &&
+           "Expected unroll factor 1 for VP vectorization.");
+    Value *Phi = State.get(getOperand(0), 0);
+    Value *EVL = State.get(getOperand(1), 0);
+    assert(EVL->getType()->getScalarSizeInBits() <=
+               Phi->getType()->getScalarSizeInBits() &&
+           "EVL type must be smaller than Phi type.");
+    EVL = Builder.CreateIntCast(EVL, Phi->getType(), /*isSigned=*/false);
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alexey-bataev wrote:

I tried but it does not work unfortunately. It would be good to have Cast VPRecipe to implement this without adding new Instruction.
The type of the EVL (and many of their users) is i32 (because of https://llvm.org/docs/LangRef.html#llvm-experimental-get-vector-length-intrinsic) and the cast is required

https://github.com/llvm/llvm-project/pull/76172