[llvm] [VPlan] Expand VPWidenIntOrFpInductionRecipe into separate recipes (PR #118638)

[Florian Hahn via llvm-commits]

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@@ -2390,6 +2380,129 @@ void VPlanTransforms::createInterleaveGroups(
   }
 }
 
+/// Expand a VPWidenIntOrFpInduction into executable recipes. for the initial
+/// value, phi and backedge value. In the followng example:
+///
+///  vector.ph:
+///  Successor(s): vector loop
+///
+///  <x1> vector loop: {
+///    vector.body:
+///      WIDEN-INDUCTION %i = phi %start, %step, %vf
+///      ...
+///      EMIT branch-on-count ...
+///    No successors
+///  }
+///
+/// WIDEN-INDUCTION will get expanded to:
+///
+///  vector.ph:
+///    ...
+///    vp<%induction> = ...
+///    vp<%inc> = ...
+///
+///  Successor(s): vector loop
+///
+///  <x1> vector loop: {
+///    vector.body:
+///      ir<%i> = WIDEN-PHI vp<%induction>, vp<%vec.ind.next>
+///      ...
+///      vp<%vec.ind.next> = add ir<%i>, vp<%inc>
+///      EMIT branch-on-count ...
+///    No successors
+///  }
+static void
+expandVPWidenIntOrFpInduction(VPWidenIntOrFpInductionRecipe *WidenIVR,
+                              VPTypeAnalysis &TypeInfo) {
+  VPlan *Plan = WidenIVR->getParent()->getPlan();
+  VPValue *Start = WidenIVR->getStartValue();
+  VPValue *Step = WidenIVR->getStepValue();
+  VPValue *VF = WidenIVR->getVFValue();
+  TruncInst *Trunc = WidenIVR->getTruncInst();
+  DebugLoc DL = WidenIVR->getDebugLoc();
+
+  // The value from the original loop to which we are mapping the new induction
+  // variable.
+  Instruction *IV = Trunc ? cast<Instruction>(Trunc) : WidenIVR->getPHINode();
+  Type *Ty = IV->getType();
+
+  const InductionDescriptor &ID = WidenIVR->getInductionDescriptor();
+  Instruction::BinaryOps AddOp;
+  Instruction::BinaryOps MulOp;
+  std::optional<FastMathFlags> FMFs;
+  if (ID.getKind() == InductionDescriptor::IK_IntInduction) {
+    AddOp = Instruction::Add;
+    MulOp = Instruction::Mul;
+  } else {
+    AddOp = ID.getInductionOpcode();
+    MulOp = Instruction::FMul;
+    FMFs = ID.getInductionBinOp()->getFastMathFlags();
+  }
+
+  // If the phi is truncated, truncate the start and step values.
+  VPBuilder Builder(Plan->getVectorPreheader());
+  if (isa<TruncInst>(IV)) {
+    assert(Start->getUnderlyingValue()->getType()->isIntegerTy() &&
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fhahn wrote:

can we use VPlan type inference instead the underlying value here?

https://github.com/llvm/llvm-project/pull/118638