[clang] [OpenMP 6.0 ]Codegen for Reduction over private variables with reduction clause (PR #134709)

[CHANDRA GHALE via cfe-commits]

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@@ -4899,6 +4899,234 @@ void CGOpenMPRuntime::emitSingleReductionCombiner(CodeGenFunction &CGF,
   }
 }
 
+void CGOpenMPRuntime::emitPrivateReduction(
+    CodeGenFunction &CGF, SourceLocation Loc, ArrayRef<const Expr *> Privates,
+    ArrayRef<const Expr *> LHSExprs, ArrayRef<const Expr *> RHSExprs,
+    ArrayRef<const Expr *> ReductionOps) {
+  if (LHSExprs.empty() || Privates.empty() || ReductionOps.empty())
+    return;
+
+  if (LHSExprs.size() != Privates.size() ||
+      LHSExprs.size() != ReductionOps.size())
+    return;
+
+  //  Create a shared global variable (__shared_reduction_var) to accumulate the
+  //  final result.
+  //
+  //  Call __kmpc_barrier to synchronize threads before initialization.
+  //
+  //  The master thread (thread_id == 0) initializes __shared_reduction_var
+  //    with the identity value or initializer.
+  //
+  //  Call __kmpc_barrier to synchronize before combining.
+  //  For each i:
+  //    - Thread enters critical section.
+  //    - Reads its private value from LHSExprs[i].
+  //    - Updates __shared_reduction_var[i] = RedOp_i(__shared_reduction_var[i],
+  //    LHSExprs[i]).
+  //    - Exits critical section.
+  //
+  //  Call __kmpc_barrier after combining.
+  //
+  //  Each thread copies __shared_reduction_var[i] back to LHSExprs[i].
+  //
+  //  Final __kmpc_barrier to synchronize after broadcasting
+  QualType PrivateType = Privates[0]->getType();
+  llvm::Type *LLVMType = CGF.ConvertTypeForMem(PrivateType);
+
+  llvm::Constant *InitVal = nullptr;
+  const OMPDeclareReductionDecl *UDR = getReductionInit(ReductionOps[0]);
+  // Determine the initial value for the shared reduction variable
+  if (!UDR) {
+    InitVal = llvm::Constant::getNullValue(LLVMType);
+    if (const auto *DRE = dyn_cast<DeclRefExpr>(Privates[0])) {
+      if (const auto *VD = dyn_cast<VarDecl>(DRE->getDecl())) {
+        const Expr *InitExpr = VD->getInit();
+        if (InitExpr && !PrivateType->isAggregateType() &&
+            !PrivateType->isAnyComplexType()) {
+          Expr::EvalResult Result;
+          if (InitExpr->EvaluateAsRValue(Result, CGF.getContext())) {
+            APValue &InitValue = Result.Val;
+            if (InitValue.isInt())
+              InitVal = llvm::ConstantInt::get(LLVMType, InitValue.getInt());
+          }
+        }
+      }
+    }
+  } else {
+    InitVal = llvm::Constant::getNullValue(LLVMType);
----------------
chandraghale wrote:

Thanks !! I have handled this now via EmitSharedInit. 

https://github.com/llvm/llvm-project/pull/134709