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

[Alexey Bataev via cfe-commits]

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@@ -4898,6 +4898,234 @@ void CGOpenMPRuntime::emitSingleReductionCombiner(CodeGenFunction &CGF,
   }
 }
 
+void CGOpenMPRuntime::emitPrivateReduction(
+    CodeGenFunction &CGF, SourceLocation Loc, const Expr *Privates,
+    const Expr *LHSExprs, const Expr *RHSExprs, const Expr *ReductionOps) {
+
+  //  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->getType();
+  llvm::Type *LLVMType = CGF.ConvertTypeForMem(PrivateType);
+
+  const OMPDeclareReductionDecl *UDR = getReductionInit(ReductionOps);
+  std::string ReductionVarNameStr;
+  if (const auto *DRE = dyn_cast<DeclRefExpr>(Privates->IgnoreParenCasts()))
+    ReductionVarNameStr = DRE->getDecl()->getNameAsString();
+  else
+    ReductionVarNameStr = "unnamed_priv_var";
+
+  // Create an internal shared variable
+  std::string SharedName =
+      CGM.getOpenMPRuntime().getName({"internal_pivate_", ReductionVarNameStr});
+  llvm::GlobalVariable *SharedVar = new llvm::GlobalVariable(
+      CGM.getModule(), LLVMType, false, llvm::GlobalValue::InternalLinkage,
+      llvm::Constant::getNullValue(LLVMType), ".omp.reduction." + SharedName,
+      nullptr, llvm::GlobalVariable::NotThreadLocal);
+
+  SharedVar->setAlignment(
+      llvm::MaybeAlign(CGF.getContext().getTypeAlign(PrivateType) / 8));
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alexey-bataev wrote:

Use OMPBuilder.getOrCreateInternalVariable

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