[llvm] Introduce DIExpression::foldConstantMath() (PR #71718)

[Shubham Sandeep Rastogi via llvm-commits]

================
@@ -1998,6 +1997,286 @@ DIExpression::constantFold(const ConstantInt *CI) {
           ConstantInt::get(getContext(), NewInt)};
 }
 
+static bool isConstantVal(uint64_t Op) {
+  return Op == dwarf::DW_OP_constu || Op == dwarf::DW_OP_consts;
+}
+
+static bool isNeutralElement(uint64_t Op, uint64_t Val) {
+  switch (Op) {
+  case dwarf::DW_OP_plus:
+  case dwarf::DW_OP_minus:
+  case dwarf::DW_OP_shl:
+  case dwarf::DW_OP_shr:
+    return Val == 0;
+  case dwarf::DW_OP_mul:
+  case dwarf::DW_OP_div:
+    return Val == 1;
+  default:
+    return false;
----------------
rastogishubham wrote:

I am not sure why that is odd, the operator passed to it can be anything, what if it is a sequence of
`DW_OP_constu, <const>, DW_OP_LLVM_arg, <arg1>, DW_OP_plus`

Op1 is DW_OP_constu and Op2 is DW_OP_LLVM_arg, so `isNeutralElement` can be called with a subsequence of `isNeutralElement(DW_OP_LLVM_arg,<const>)` which is why the default case exists

https://github.com/llvm/llvm-project/pull/71718