[SYCL] Don't diagnose checks in a discarded statement.

clang/include/clang/AST/Stmt.h

@@ -2080,6 +2080,7 @@ class IfStmt final
   /// If this is an 'if constexpr', determine which substatement will be taken.
   /// Otherwise, or if the condition is value-dependent, returns None.
   Optional<const Stmt*> getNondiscardedCase(const ASTContext &Ctx) const;
+  Optional<Stmt *> getNondiscardedCase(const ASTContext &Ctx);
 
   bool isObjCAvailabilityCheck() const;
 

clang/include/clang/Analysis/CallGraph.h

@@ -29,6 +29,7 @@
 
 namespace clang {
 
+class ASTContext;
 class CallGraphNode;
 class Decl;
 class DeclContext;
@@ -51,6 +52,12 @@ class CallGraph : public RecursiveASTVisitor<CallGraph> {
   /// This is a virtual root node that has edges to all the functions.
   CallGraphNode *Root;
 
+  /// A setting to determine whether this should include calls that are done in
+  /// a constant expression's context. This DOES require the ASTContext object
+  /// for constexpr-if, so setting it requires a valid ASTContext.
+  bool shouldSkipConstexpr = false;
+  ASTContext *Ctx;
+
 public:
   CallGraph();
   ~CallGraph();
@@ -66,7 +73,7 @@ class CallGraph : public RecursiveASTVisitor<CallGraph> {
   /// Determine if a declaration should be included in the graph.
   static bool includeInGraph(const Decl *D);
 
-  /// Determine if a declaration should be included in the graph for the 
+  /// Determine if a declaration should be included in the graph for the
   /// purposes of being a callee. This is similar to includeInGraph except
   /// it permits declarations, not just definitions.
   static bool includeCalleeInGraph(const Decl *D);
@@ -138,6 +145,16 @@ class CallGraph : public RecursiveASTVisitor<CallGraph> {
   bool shouldWalkTypesOfTypeLocs() const { return false; }
   bool shouldVisitTemplateInstantiations() const { return true; }
   bool shouldVisitImplicitCode() const { return true; }
+  bool shouldVisitConstantExpressions() const { return false; }
+  bool shouldSkipConstantExpressions() const { return shouldSkipConstexpr; }
+  void setSkipConstantExpressions(ASTContext &Context) {
+    Ctx = &Context;
+    shouldSkipConstexpr = true;
+  }
+  ASTContext &getASTContext() {
+    assert(Ctx);
+    return *Ctx;
+  }
 
 private:
   /// Add the given declaration to the call graph.

clang/lib/AST/Stmt.cpp

@@ -995,6 +995,12 @@ Optional<const Stmt*> IfStmt::getNondiscardedCase(const ASTContext &Ctx) const {
   return !getCond()->EvaluateKnownConstInt(Ctx) ? getElse() : getThen();
 }
 
+Optional<Stmt *> IfStmt::getNondiscardedCase(const ASTContext &Ctx) {
+  if (!isConstexpr() || getCond()->isValueDependent())
+    return None;
+  return !getCond()->EvaluateKnownConstInt(Ctx) ? getElse() : getThen();
+}
+
 ForStmt::ForStmt(const ASTContext &C, Stmt *Init, Expr *Cond, VarDecl *condVar,
                  Expr *Inc, Stmt *Body, SourceLocation FL, SourceLocation LP,
                  SourceLocation RP)

clang/lib/Analysis/CallGraph.cpp

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/Analysis/CallGraph.h"
+#include "clang/AST/ASTContext.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclBase.h"
 #include "clang/AST/DeclObjC.h"
@@ -136,6 +137,37 @@ class CGBuilder : public StmtVisitor<CGBuilder> {
     }
   }
 
+  void VisitIfStmt(IfStmt *If) {
+    if (G->shouldSkipConstantExpressions()) {
+      if (llvm::Optional<Stmt *> ActiveStmt =
+              If->getNondiscardedCase(G->getASTContext())) {
+        if (*ActiveStmt)
+          this->Visit(*ActiveStmt);
+        return;
+      }
+    }
+
+    StmtVisitor::VisitIfStmt(If);
+  }
+
+  void VisitDeclStmt(DeclStmt *DS) {
+    if (G->shouldSkipConstantExpressions()) {
+      auto IsConstexprVarDecl = [](Decl *D) {
+        if (const auto *VD = dyn_cast<VarDecl>(D))
+          return VD->isConstexpr();
+        return false;
+      };
+      if (llvm::any_of(DS->decls(), IsConstexprVarDecl)) {
+        assert(llvm::all_of(DS->decls(), IsConstexprVarDecl) &&
+               "Situation where a decl-group would be a mix of decl types, or "
+               "constexpr and not?");
+        return;
+      }
+    }
+
+    StmtVisitor::VisitDeclStmt(DS);
+  }
+
   void VisitChildren(Stmt *S) {
     for (Stmt *SubStmt : S->children())
       if (SubStmt)

clang/lib/Sema/SemaSYCL.cpp

@@ -548,6 +548,7 @@ class DeviceFunctionTracker {
 
 public:
   DeviceFunctionTracker(Sema &S) : SemaRef(S) {
+    CG.setSkipConstantExpressions(S.Context);
     CG.addToCallGraph(S.getASTContext().getTranslationUnitDecl());
     CollectSyclExternalFuncs();
   }