[OpenMP] `omp begin/end declare variant` - part 2, sema ("+CG")

This is the second part loosely extracted from D71179 and cleaned up.

This patch provides semantic analysis support for `omp begin/end declare
variant`, mostly as defined in OpenMP technical report 8 (TR8) [0].
The sema handling makes code generation obsolete as we generate "the
right" calls that can just be handled as usual. This handling also
applies to the existing, albeit problematic, `omp declare variant
support`. As a consequence a lot of unneeded code generation and
complexity is removed.

A major purpose of this patch is to provide proper `math.h`/`cmath`
support for OpenMP target offloading. See PR42061, PR42798, PR42799. The
current code was developed with this feature in mind, see [1].

The logic is as follows:

If we have seen a `#pragma omp begin declare variant match(<SELECTOR>)`
but not the corresponding `end declare variant`, and we find a function
definition we will:
  1) Create a function declaration for the definition we were about to generate.
  2) Create a function definition but with a mangled name (according to
     `<SELECTOR>`).
  3) Annotate the declaration with the `OMPDeclareVariantAttr`, the same
     one used already for `omp declare variant`, using and the mangled
     function definition as specialization for the context defined by
     `<SELECTOR>`.

When a call is created we inspect it. If the target has an
`OMPDeclareVariantAttr` attribute we try to specialize the call. To this
end, all variants are checked, the best applicable one is picked and a
new call to the specialization is created. The new call is used instead
of the original one to the base function. To keep the AST printing and
tooling possible we utilize the PseudoObjectExpr. The original call is
the syntactic expression, the specialized call is the semantic
expression.

[0] https://www.openmp.org/wp-content/uploads/openmp-TR8.pdf
[1] https://reviews.llvm.org/D61399#change-496lQkg0mhRN

Reviewers: kiranchandramohan, ABataev, RaviNarayanaswamy, gtbercea, grokos, sdmitriev, JonChesterfield, hfinkel, fghanim, aaron.ballman

Subscribers: bollu, guansong, openmp-commits, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D75779

1 files changed, 0 insertions, 58 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index eb678f80600c..fbde1bf5cab7 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -2615,11 +2615,6 @@ void CodeGenModule::EmitGlobal(GlobalDecl GD) {
     return;
   }
 
-    // Check if this must be emitted as declare variant.
-  if (LangOpts.OpenMP && isa<FunctionDecl>(Global) && OpenMPRuntime &&
-      OpenMPRuntime->emitDeclareVariant(GD, /*IsForDefinition=*/false))
-    return;
-
   // If we're deferring emission of a C++ variable with an
   // initializer, remember the order in which it appeared in the file.
   if (getLangOpts().CPlusPlus && isa<VarDecl>(Global) &&
@@ -2825,50 +2820,6 @@ void CodeGenModule::EmitMultiVersionFunctionDefinition(GlobalDecl GD,
     EmitGlobalFunctionDefinition(GD, GV);
 }
 
-void CodeGenModule::emitOpenMPDeviceFunctionRedefinition(
-    GlobalDecl OldGD, GlobalDecl NewGD, llvm::GlobalValue *GV) {
-  assert(getLangOpts().OpenMP && getLangOpts().OpenMPIsDevice &&
-         OpenMPRuntime && "Expected OpenMP device mode.");
-  const auto *D = cast<FunctionDecl>(OldGD.getDecl());
-
-  // Compute the function info and LLVM type.
-  const CGFunctionInfo &FI = getTypes().arrangeGlobalDeclaration(OldGD);
-  llvm::FunctionType *Ty = getTypes().GetFunctionType(FI);
-
-  // Get or create the prototype for the function.
-  if (!GV || (GV->getType()->getElementType() != Ty)) {
-    GV = cast<llvm::GlobalValue>(GetOrCreateLLVMFunction(
-        getMangledName(OldGD), Ty, GlobalDecl(), /*ForVTable=*/false,
-        /*DontDefer=*/true, /*IsThunk=*/false, llvm::AttributeList(),
-        ForDefinition));
-    SetFunctionAttributes(OldGD, cast<llvm::Function>(GV),
-                          /*IsIncompleteFunction=*/false,
-                          /*IsThunk=*/false);
-  }
-  // We need to set linkage and visibility on the function before
-  // generating code for it because various parts of IR generation
-  // want to propagate this information down (e.g. to local static
-  // declarations).
-  auto *Fn = cast<llvm::Function>(GV);
-  setFunctionLinkage(OldGD, Fn);
-
-  // FIXME: this is redundant with part of
-  // setFunctionDefinitionAttributes
-  setGVProperties(Fn, OldGD);
-
-  MaybeHandleStaticInExternC(D, Fn);
-
-  maybeSetTrivialComdat(*D, *Fn);
-
-  CodeGenFunction(*this).GenerateCode(NewGD, Fn, FI);
-
-  setNonAliasAttributes(OldGD, Fn);
-  SetLLVMFunctionAttributesForDefinition(D, Fn);
-
-  if (D->hasAttr<AnnotateAttr>())
-    AddGlobalAnnotations(D, Fn);
-}
-
 void CodeGenModule::EmitGlobalDefinition(GlobalDecl GD, llvm::GlobalValue *GV) {
   const auto *D = cast<ValueDecl>(GD.getDecl());
 
@@ -3183,10 +3134,6 @@ llvm::Constant *CodeGenModule::GetOrCreateLLVMFunction(
         EmitGlobal(GDDef);
       }
     }
-    // Check if this must be emitted as declare variant and emit reference to
-    // the the declare variant function.
-    if (LangOpts.OpenMP && OpenMPRuntime)
-      (void)OpenMPRuntime->emitDeclareVariant(GD, /*IsForDefinition=*/true);
 
     if (FD->isMultiVersion()) {
       if (FD->hasAttr<TargetAttr>())
@@ -4518,11 +4465,6 @@ void CodeGenModule::HandleCXXStaticMemberVarInstantiation(VarDecl *VD) {
 
 void CodeGenModule::EmitGlobalFunctionDefinition(GlobalDecl GD,
                                                  llvm::GlobalValue *GV) {
-  // Check if this must be emitted as declare variant.
-  if (LangOpts.OpenMP && OpenMPRuntime &&
-      OpenMPRuntime->emitDeclareVariant(GD, /*IsForDefinition=*/true))
-    return;
-
   const auto *D = cast<FunctionDecl>(GD.getDecl());
 
   // Compute the function info and LLVM type.