[OpenMP] Use the OpenMPIRBuilder for `omp parallel`

This allows to use the OpenMPIRBuilder for parallel regions. Code was
extracted from D61953 and adapted to work with the new version (D70109).

All but one feature should be supported. An update of this patch will
provide test coverage and privatization other than shared.

Reviewed By: fghanim

Differential Revision: https://reviews.llvm.org/D70290

2 files changed, 30 insertions, 1 deletions

diff --git a/llvm/lib/Frontend/OpenMP/OMPConstants.cpp b/llvm/lib/Frontend/OpenMP/OMPConstants.cpp
index 67d88ffb17a..ec0733903e9 100644
--- a/llvm/lib/Frontend/OpenMP/OMPConstants.cpp
+++ b/llvm/lib/Frontend/OpenMP/OMPConstants.cpp
@@ -65,7 +65,7 @@ void llvm::omp::types::initializeTypes(Module &M) {
 #define OMP_TYPE(VarName, InitValue) VarName = InitValue;
 #define OMP_FUNCTION_TYPE(VarName, IsVarArg, ReturnType, ...)                  \
   VarName = FunctionType::get(ReturnType, {__VA_ARGS__}, IsVarArg);            \
-  VarName##Ptr = PointerType::getUnqual(T);
+  VarName##Ptr = PointerType::getUnqual(VarName);
 #define OMP_STRUCT_TYPE(VarName, StructName, ...)                              \
   T = M.getTypeByName(StructName);                                             \
   if (!T)                                                                      \
diff --git a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
index 57db40775c0..739c2998baa 100644
--- a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
+++ b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
@@ -18,6 +18,7 @@
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/DebugInfo.h"
+#include "llvm/IR/MDBuilder.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Error.h"
@@ -501,10 +502,21 @@ IRBuilder<>::InsertPoint OpenMPIRBuilder::CreateParallel(
       dbgs() << " PBR: " << BB->getName() << "\n";
   });
 
+  // Add some known attributes to the outlined function.
   Function *OutlinedFn = Extractor.extractCodeRegion(CEAC);
+  OutlinedFn->addParamAttr(0, Attribute::NoAlias);
+  OutlinedFn->addParamAttr(1, Attribute::NoAlias);
+  OutlinedFn->addFnAttr(Attribute::NoUnwind);
+  OutlinedFn->addFnAttr(Attribute::NoRecurse);
+
   LLVM_DEBUG(dbgs() << "After      outlining: " << *UI->getFunction() << "\n");
   LLVM_DEBUG(dbgs() << "   Outlined function: " << *OutlinedFn << "\n");
 
+  // For compability with the clang CG we move the outlined function after the
+  // one with the parallel region.
+  OutlinedFn->removeFromParent();
+  M.getFunctionList().insertAfter(OuterFn->getIterator(), OutlinedFn);
+
   // Remove the artificial entry introduced by the extractor right away, we
   // made our own entry block after all.
   {
@@ -535,6 +547,23 @@ IRBuilder<>::InsertPoint OpenMPIRBuilder::CreateParallel(
   RealArgs.append(CI->arg_begin() + /* tid & bound tid */ 2, CI->arg_end());
 
   FunctionCallee RTLFn = getOrCreateRuntimeFunction(OMPRTL___kmpc_fork_call);
+  if (auto *F = dyn_cast<llvm::Function>(RTLFn.getCallee())) {
+    if (!F->hasMetadata(llvm::LLVMContext::MD_callback)) {
+      llvm::LLVMContext &Ctx = F->getContext();
+      MDBuilder MDB(Ctx);
+      // Annotate the callback behavior of the __kmpc_fork_call:
+      //  - The callback callee is argument number 2 (microtask).
+      //  - The first two arguments of the callback callee are unknown (-1).
+      //  - All variadic arguments to the __kmpc_fork_call are passed to the
+      //    callback callee.
+      F->addMetadata(
+          llvm::LLVMContext::MD_callback,
+          *llvm::MDNode::get(Ctx, {MDB.createCallbackEncoding(
+                                      2, {-1, -1},
+                                      /* VarArgsArePassed */ true)}));
+    }
+  }
+
   Builder.CreateCall(RTLFn, RealArgs);
 
   LLVM_DEBUG(dbgs() << "With fork_call placed: "