[llvm] [DirectX] Make DXILOpLowering split vector coordinates, offsets, and gradient operands (PR #223091)

[Joshua Batista via llvm-commits]

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@@ -639,22 +640,56 @@ class OpLowerer {
     });
   }
 
+  /// Recover the scalar components of `Vec` from the `insertelement` chain that
+  /// built it. Since we run after the scalarizer, such a chain is usually just
+  /// a temporary gathered to pass the vector to a call.
+  static void collectInsertedElements(Value *Vec,
+                                      MutableArrayRef<Value *> Elements) {
+    unsigned NumElts = cast<FixedVectorType>(Vec->getType())->getNumElements();
+    assert(NumElts <= Elements.size() && "Not enough room for the components");
+
+    SmallVector<InsertElementInst *, 4> Chain;
+    for (auto *IEI = dyn_cast<InsertElementInst>(Vec); IEI;
+         IEI = dyn_cast<InsertElementInst>(IEI->getOperand(0))) {
+      if (!isa<ConstantInt>(IEI->getOperand(2)))
+        break; // This break should never happen below SM6.9.
+      Chain.push_back(IEI);
+    }
+
+    // Replay element insertion from the innermost first, so that a repeated
+    // index ends up holding the live value.
+    while (!Chain.empty()) {
+      InsertElementInst *IEI = Chain.pop_back_val();
+      uint64_t IndexVal = cast<ConstantInt>(IEI->getOperand(2))->getZExtValue();
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bob80905 wrote:

double checking: is there an implicit cast between ConstantInt and uint64_t, or should we call some helper to get the value?

https://github.com/llvm/llvm-project/pull/223091