[clang] [NFC][Clang][OpenMP] Add helper functions/utils for finding/comparing attach base-ptrs. (PR #155625)

[Abhinav Gaba via cfe-commits]

================
@@ -6765,12 +6765,255 @@ llvm::Value *CGOpenMPRuntime::emitNumThreadsForTargetDirective(
 namespace {
 LLVM_ENABLE_BITMASK_ENUMS_IN_NAMESPACE();
 
+/// Utility to compare expression locations.
+/// Returns true if expr-loc of LHS is less-than that of RHS.
+/// This function asserts that both expressions have valid expr-locations.
+static bool compareExprLocs(const Expr *LHS, const Expr *RHS) {
+  // Assert that neither LHS nor RHS can be null
+  assert(LHS && "LHS expression cannot be null");
+  assert(RHS && "RHS expression cannot be null");
+
+  // Get source locations
+  SourceLocation LocLHS = LHS->getExprLoc();
+  SourceLocation LocRHS = RHS->getExprLoc();
+
+  // Assert that we have valid source locations
+  assert(LocLHS.isValid() && "LHS expression must have valid source location");
+  assert(LocRHS.isValid() && "RHS expression must have valid source location");
+
+  // Compare source locations for deterministic ordering
+  return LocLHS < LocRHS;
----------------
abhinavgaba wrote:

I was trying to think of a case where the exprs we are comparing are from different files, but I couldn't think of any for attach-ptr exprs. Do you have a case in mind?

For the purpose for attach-ptr expr comparisons, we do the comparison on a per directive basis, as part of MappableExprHandler, and the ExprLocs are those for the expressions within the clause list of that directive. For example:

```c
#pragma omp target data map(s1.p1[0], s1.p2[2])
```

Here s1.p1 and s1.p2's ExprLocs should point to the occurrence of these expressions within this directive.


I know that we insert inlined maps for outer structs with inner structs that have declare-mappers, like:

```c
struct S {
  int *p;
};
#pragma omp declare mapper(default: s1) map(s1.p[0:1])

struct T {
  S s1;
  int *q;
};

T *tp;

#pragma omp target data map(tp[0]), map(from: tp[0].q) // implicit: map(tp[0].s1)

```
However, in this case, the attach-pointer-expr for the implicit map for `tp[0].s1` will still be `tp`, whose expr location should come from `map(tp[0])` on the line with `pragma omp target data`


https://github.com/llvm/llvm-project/pull/155625