[clang] [OpenMP] Support capturing structured bindings in OpenMP regions. (PR #190832)

[Zahira Ammarguellat via cfe-commits]

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@@ -1575,6 +1606,37 @@ void CodeGenFunction::EmitOMPReductionClauseInit(
   auto *IPriv = Privates.begin();
   for (const Expr *IRef : Shareds) {
     const auto *PrivateVD = cast<VarDecl>(cast<DeclRefExpr>(*IPriv)->getDecl());
+    const BindingDecl *BD = nullptr;
+    if (const auto *DRE = dyn_cast<DeclRefExpr>(IRef->IgnoreParenImpCasts()))
+      BD = dyn_cast<BindingDecl>(DRE->getDecl());
+    if (BD) {
+      // Emit the private VarDecl with reduction initialization.
+      EmitDecl(*PrivateVD);
+      Address PrivateAddr = GetAddrOfLocalVar(PrivateVD);
+
+      // Register the BindingDecl with the private address.
+      bool IsRegistered = PrivateScope.addPrivate(BD, PrivateAddr);
+      assert(IsRegistered && "private binding already registered as private");
+      (void)IsRegistered;
+
+      // Get the original BindingDecl address for LHSVD registration.
+      DeclRefExpr BindingDRE(getContext(), const_cast<BindingDecl *>(BD),
+                             /*RefersToEnclosingVariableOrCapture=*/true,
+                             BD->getType(), VK_LValue, IRef->getExprLoc());
+      LValue OriginalLVal = EmitLValue(&BindingDRE);
+      Address OriginalAddr = OriginalLVal.getAddress();
+
+      // Register LHSVD/RHSVD for reduction operation.
+      const auto *LHSVD = cast<VarDecl>(cast<DeclRefExpr>(*ILHS)->getDecl());
+      const auto *RHSVD = cast<VarDecl>(cast<DeclRefExpr>(*IRHS)->getDecl());
+      PrivateScope.addPrivate(LHSVD, OriginalAddr);
+      PrivateScope.addPrivate(RHSVD, PrivateAddr);
+      ++Count;
+      ++ILHS;
+      ++IRHS;
+      ++IPriv;
+      continue;
----------------
zahiraam wrote:

The `BindingDecl` path cannot use  `RedCG.emitSharedOrigLValue(`) because that calls `EmitOMPSharedLValue()` which crashes when trying to emit a `BindingDecl` reference in the outlined region  (the `DecompositionDecl` context is broken). Instead, we emit the original `BindingDecl` address directly and register`LHSVD/RHSVD` manually, which achieves the same writeback effect. I've added detailed comments explaining this limitation.

https://github.com/llvm/llvm-project/pull/190832