[llvm] [VPlan] Introduce ExitPhi VPInstruction, use to create phi for FOR. (PR #94760)

[Florian Hahn via llvm-commits]

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@@ -3386,33 +3380,6 @@ void InnerLoopVectorizer::fixVectorizedLoop(VPTransformState &State,
                                VF.getKnownMinValue() * UF);
 }
 
-void InnerLoopVectorizer::fixFixedOrderRecurrence(VPLiveOut *LO,
-                                                  VPTransformState &State) {
-  // Extract the last vector element in the middle block. This will be the
-  // initial value for the recurrence when jumping to the scalar loop.
-  VPValue *VPExtract = LO->getOperand(0);
-  using namespace llvm::VPlanPatternMatch;
-  assert(match(VPExtract, m_VPInstruction<VPInstruction::ExtractFromEnd>(
-                              m_VPValue(), m_VPValue())) &&
-         "FOR LiveOut expects to use an extract from end.");
-  Value *ResumeScalarFOR = State.get(VPExtract, UF - 1, true);
-
-  // Fix the initial value of the original recurrence in the scalar loop.
-  PHINode *ScalarHeaderPhi = LO->getPhi();
-  auto *InitScalarFOR =
-      ScalarHeaderPhi->getIncomingValueForBlock(LoopScalarPreHeader);
-  Builder.SetInsertPoint(LoopScalarPreHeader, LoopScalarPreHeader->begin());
-  auto *ScalarPreheaderPhi =
-      Builder.CreatePHI(ScalarHeaderPhi->getType(), 2, "scalar.recur.init");
-  for (auto *BB : predecessors(LoopScalarPreHeader)) {
-    auto *Incoming = BB == LoopMiddleBlock ? ResumeScalarFOR : InitScalarFOR;
-    ScalarPreheaderPhi->addIncoming(Incoming, BB);
-  }
-  ScalarHeaderPhi->setIncomingValueForBlock(LoopScalarPreHeader,
-                                            ScalarPreheaderPhi);
----------------
fhahn wrote:

At the moment, ResumePhi won't generate any extracts, as it will be fed by the extracted scalar resume value of the FOR. Possibly more accurately to mark ResumePhi as only having its first lane used instead of vector-to-scalar. (Done in latest version)

https://github.com/llvm/llvm-project/pull/94760