Handle ConstantExpr correctly in SelectionDAGBuilder
This change fixes a bug in SelectionDAGBuilder::visitInsertValue and SelectionDAGBuilder::visitExtractValue where constant expressions (InsertValueConstantExpr and ExtractValueConstantExpr) would be treated as non-constant instructions (InsertValueInst and ExtractValueInst). This bug resulted in an incorrect memory access, which manifested as an assertion failure in SDValue::SDValue.
Fixes PR#33094.
Submitted on behalf of @Praetonus (Benoit Vey)
Differential Revision: https://reviews.llvm.org/D34538
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307502
91177308-0d34-0410-b5e6-
96231b3b80d8