[ConstantFold] Fold extractelement of getelementptr

Summary:
Getelementptr has vector type if any of its operands are vectors
(the scalar operands being implicitly broadcast to all vector elements).
Extractelement applied to a vector getelementptr can be folded by
applying the extractelement in turn to all of the vector operands.

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69379

1 files changed, 29 insertions, 6 deletions

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 71fa795..84b117d 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -792,13 +792,36 @@ Constant *llvm::ConstantFoldExtractElementInstruction(Constant *Val,
   if (isa<UndefValue>(Val) || isa<UndefValue>(Idx))
     return UndefValue::get(Val->getType()->getVectorElementType());
 
-  if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Idx)) {
-    // ee({w,x,y,z}, wrong_value) -> undef
-    if (CIdx->uge(Val->getType()->getVectorNumElements()))
-      return UndefValue::get(Val->getType()->getVectorElementType());
-    return Val->getAggregateElement(CIdx->getZExtValue());
+  auto *CIdx = dyn_cast<ConstantInt>(Idx);
+  if (!CIdx)
+    return nullptr;
+
+  // ee({w,x,y,z}, wrong_value) -> undef
+  if (CIdx->uge(Val->getType()->getVectorNumElements()))
+    return UndefValue::get(Val->getType()->getVectorElementType());
+
+  // ee (gep (ptr, idx0, ...), idx) -> gep (ee (ptr, idx), ee (idx0, idx), ...)
+  if (auto *CE = dyn_cast<ConstantExpr>(Val)) {
+    if (CE->getOpcode() == Instruction::GetElementPtr) {
+      SmallVector<Constant *, 8> Ops;
+      Ops.reserve(CE->getNumOperands());
+      for (unsigned i = 0, e = CE->getNumOperands(); i != e; ++i) {
+        Constant *Op = CE->getOperand(i);
+        if (Op->getType()->isVectorTy()) {
+          Constant *ScalarOp = ConstantFoldExtractElementInstruction(Op, Idx);
+          if (!ScalarOp)
+            return  nullptr;
+          Ops.push_back(ScalarOp);
+        } else
+          Ops.push_back(Op);
+      }
+      return CE->getWithOperands(Ops, CE->getType()->getVectorElementType(),
+                                 false,
+                                 Ops[0]->getType()->getPointerElementType());
+    }
   }
-  return nullptr;
+
+  return Val->getAggregateElement(CIdx);
 }
 
 Constant *llvm::ConstantFoldInsertElementInstruction(Constant *Val,