[llvm] [VPlan] Use pointer to member 0 as VPInterleaveRecipe's pointer arg. (PR #106431)

[via llvm-commits]

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@@ -1601,9 +1606,38 @@ void VPlanTransforms::createInterleaveGroups(
 
     bool NeedsMaskForGaps =
         IG->requiresScalarEpilogue() && !ScalarEpilogueAllowed;
-    auto *VPIG = new VPInterleaveRecipe(IG, Recipe->getAddr(), StoredValues,
-                                        Recipe->getMask(), NeedsMaskForGaps);
-    VPIG->insertBefore(Recipe);
+
+    Instruction *IRInsertPos = IG->getInsertPos();
+    auto *InsertPos =
+        cast<VPWidenMemoryRecipe>(RecipeBuilder.getRecipe(IRInsertPos));
+
+    // Get or create the start address for the interleave group.
+    auto *Start =
+        cast<VPWidenMemoryRecipe>(RecipeBuilder.getRecipe(IG->getMember(0)));
+    VPValue *Addr = Start->getAddr();
+    if (!VPDT.properlyDominates(Addr->getDefiningRecipe(), InsertPos)) {
+      bool InBounds = false;
+      if (auto *Gep = dyn_cast<GetElementPtrInst>(
+              getLoadStorePointerOperand(IRInsertPos)->stripPointerCasts()))
+        InBounds = Gep->isInBounds();
+
+      // We cannot re-use the address of the first member because it does not
+      // dominate the insert position. Use the address of the insert position
+      // and create a PtrAdd to adjust the index to start at the first member.
+      APInt Offset(32,
+                   getLoadStoreType(IRInsertPos)->getScalarSizeInBits() / 8 *
+                       IG->getIndex(IRInsertPos),
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ayalz wrote:

Worth asserting Offset or index of IRInsertPos is non zero?
I.e., if insert pos is the first member, its address operand must dominate it.

https://github.com/llvm/llvm-project/pull/106431