address comments

Author: Chen Zheng

clang/lib/CodeGen/CGCall.cpp

@@ -5760,16 +5760,22 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
             CGM.getDiags().Report(Loc, diag::err_ppc_impossible_musttail) << 0;
           else if (Call->isIndirectCall())
             CGM.getDiags().Report(Loc, diag::err_ppc_impossible_musttail) << 1;
-          else if (isa_and_nonnull<FunctionDecl>(TargetDecl) &&
-                   cast<FunctionDecl>(TargetDecl)->isWeak())
-            CGM.getDiags().Report(Loc, diag::err_ppc_impossible_musttail) << 2;
-          else if (isa_and_nonnull<FunctionDecl>(TargetDecl) &&
-                   !cast<FunctionDecl>(TargetDecl)->isDefined())
-            // The undefined callee may be a forward declaration. Without
-            // knowning all symbols in the module, we won't know the symbol is
-            // defined or not. Collect all these symbols for later diagnosing.
-            CGM.addUndefinedGlobalForTailCall(
-                {cast<FunctionDecl>(TargetDecl), Loc});
+          else if (isa_and_nonnull<FunctionDecl>(TargetDecl)) {
+            if (!cast<FunctionDecl>(TargetDecl)->isDefined())
+              // The undefined callee may be a forward declaration. Without
+              // knowning all symbols in the module, we won't know the symbol is
+              // defined or not. Collect all these symbols for later diagnosing.
+              CGM.addUndefinedGlobalForTailCall(
+                  {cast<FunctionDecl>(TargetDecl), Loc});
+            else {
+              llvm::GlobalValue::LinkageTypes Linkage = CGM.getFunctionLinkage(
+                  GlobalDecl(cast<FunctionDecl>(TargetDecl)));
+              if (llvm::GlobalValue::isWeakForLinker(Linkage) ||
+                  llvm::GlobalValue::isDiscardableIfUnused(Linkage))
+                CGM.getDiags().Report(Loc, diag::err_ppc_impossible_musttail)
+                    << 2;
+            }
+          }
         }
       }
       Call->setTailCallKind(llvm::CallInst::TCK_MustTail);

clang/lib/CodeGen/CodeGenModule.cpp

@@ -1400,6 +1400,13 @@ void CodeGenModule::Release() {
     for (auto &I : MustTailCallUndefinedGlobals) {
       if (!I.first->isDefined())
         getDiags().Report(I.second, diag::err_ppc_impossible_musttail) << 2;
+      else {
+        StringRef MangledName = getMangledName(GlobalDecl(I.first));
+        llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
+        if (!Entry || Entry->isWeakForLinker() ||
+            Entry->isDeclarationForLinker())
+          getDiags().Report(I.second, diag::err_ppc_impossible_musttail) << 2;
+      }
     }
   }
 }

clang/lib/CodeGen/CodeGenModule.h

@@ -488,8 +488,8 @@ class CodeGenModule : public CodeGenTypeCache {
   // When a tail call is performed on an "undefined" symbol, on PPC without pc
   // relative feature, the tail call is not allowed. In "EmitCall" for such
   // tail calls, the "undefined" symbols may be forward declarations, their
-  // definitions are provided in the module but after the callsites. For such
-  // tail calls, diagnose message should be not emitted.
+  // definitions are provided in the module after the callsites. For such tail
+  // calls, diagnose message should not be emitted.
   llvm::SmallSetVector<std::pair<const FunctionDecl *, SourceLocation>, 4>
       MustTailCallUndefinedGlobals;
 

clang/test/CodeGen/PowerPC/musttail-forward-declaration-inline.c

@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 %s -triple powerpc64le-unknown-linux-gnu -o /dev/null -emit-llvm -verify
+// RUN: %clang_cc1 %s -triple powerpc64-unknown-linux-gnu -o /dev/null -emit-llvm -verify
+
+inline int func2(int i);
+int external_call2(int i) {
+  // expected-error@+1 {{'musttail' attribute for this call is impossible because external calls can not be tail called on PPC}}
+  [[clang::musttail]] return func2(i);
+}
+
+inline int func2(int i) {
+  return 0;
+}

clang/test/CodeGen/PowerPC/musttail-forward-declaration-weak.c

@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 %s -triple powerpc64le-unknown-linux-gnu -o /dev/null -emit-llvm -verify
+// RUN: %clang_cc1 %s -triple powerpc64-unknown-linux-gnu -o /dev/null -emit-llvm -verify
+
+int func2(int i);
+int external_call2(int i) {
+  // expected-error@+1 {{'musttail' attribute for this call is impossible because external calls can not be tail called on PPC}}
+  [[clang::musttail]] return func2(i);
+}
+
+__attribute__((weak)) int func2(int i) {
+  return 0;
+}

clang/test/CodeGen/PowerPC/musttail-inline.c

@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 %s -triple powerpc64-unknown-linux-gnu -o /dev/null -emit-llvm -verify
+// RUN: %clang_cc1 %s -triple powerpc64le-unknown-linux-gnu -o /dev/null -emit-llvm -verify
+
+inline int foo(int x) {
+  return x;
+}
+
+int bar(int x)
+{
+  // expected-error@+1 {{'musttail' attribute for this call is impossible because external calls can not be tail called on PPC}}
+  [[clang::musttail]] return foo(1);
+}