[lld] [llvm] [clang] [compiler-rt] [lldb] [libc] [clang-tools-extra] [flang] [libcxx] [VPlan] Implement cloning of VPlans. (PR #73158)

[via llvm-commits]

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@@ -982,6 +1037,92 @@ void VPlan::updateDominatorTree(DominatorTree *DT, BasicBlock *LoopHeaderBB,
   assert(DT->verify(DominatorTree::VerificationLevel::Fast));
 }
 
+static void remapOperands(VPBlockBase *Entry, VPBlockBase *NewEntry,
+                          DenseMap<VPValue *, VPValue *> &Old2NewVPValues) {
+  // Update the operands of all cloned recipes starting at NewEntry. This
+  // traverses all reachable blocks. This is done in two steps, to handle cycles
+  // in PHI recipes.
+  ReversePostOrderTraversal<VPBlockDeepTraversalWrapper<VPBlockBase *>>
+      OldDeepRPOT(Entry);
+  ReversePostOrderTraversal<VPBlockDeepTraversalWrapper<VPBlockBase *>>
+      NewDeepRPOT(NewEntry);
+  // First, collect all mappings from old to new VPValues defined by cloned
+  // recipes.
+  for (const auto &[OldBB, NewBB] :
+       zip(VPBlockUtils::blocksOnly<VPBasicBlock>(OldDeepRPOT),
+           VPBlockUtils::blocksOnly<VPBasicBlock>(NewDeepRPOT))) {
+    assert(OldBB->getRecipeList().size() == NewBB->getRecipeList().size() &&
+           "blocks must have the same number of recipes");
+
+    for (const auto &[OldR, NewR] : zip(*OldBB, *NewBB)) {
+      assert(OldR.getNumOperands() == NewR.getNumOperands() &&
+             "recipes must have the same number of operands");
+      assert(OldR.getNumDefinedValues() == NewR.getNumDefinedValues() &&
+             "recipes must define the same number of operands");
+      for (const auto &[OldV, NewV] :
+           zip(OldR.definedValues(), NewR.definedValues()))
+        Old2NewVPValues[OldV] = NewV;
+    }
+  }
+
+  // Update all operands to use cloned VPValues.
+  for (VPBasicBlock *NewBB :
+       VPBlockUtils::blocksOnly<VPBasicBlock>(NewDeepRPOT)) {
+    for (VPRecipeBase &NewR : *NewBB)
+      for (unsigned I = 0, E = NewR.getNumOperands(); I != E; ++I) {
+        VPValue *NewOp = Old2NewVPValues.lookup(NewR.getOperand(I));
+        NewR.setOperand(I, NewOp);
+      }
+  }
+}
+
+VPlan *VPlan::clone() {
+  DenseMap<VPValue *, VPValue *> Old2NewVPValues;
+
+  // Clone blocks.
+  VPBlockBase *NewPreheader = cloneVPB(Preheader);
+  const auto &[NewEntry, __] = cloneSESE(getEntry());
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ayalz wrote:

Consistency nit: use Preheader and Entry, or getPreheader() and getEntry().

https://github.com/llvm/llvm-project/pull/73158