address comments

Author: Chen Zheng

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -3841,9 +3841,12 @@ def note_cannot_use_trivial_abi_reason : Note<
   "it is polymorphic|"
   "it has a base of a non-trivial class type|it has a virtual base|"
   "it has a __weak field|it has a field of a non-trivial class type}1">;
-def warn_ppc_musttail_maybe_ignored: Warning<
-  "'musttail' attribute may be ignored on ppc targets">,
-  InGroup<IgnoredAttributes>;
+def err_ppc_impossible_musttail: Error<
+  "'musttail' attribute for this call is impossible because %select{"
+  "long calls can not be tail called|"
+  "indirect calls can not be tail called|"
+  "external calls can not be tail called}0"
+  >;
 def err_aix_musttail_unsupported: Error<
   "'musttail' attribute is not supported on AIX">;
 

clang/lib/Basic/Targets/PPC.cpp

@@ -93,6 +93,8 @@ bool PPCTargetInfo::handleTargetFeatures(std::vector<std::string> &Features,
       HasQuadwordAtomics = true;
     } else if (Feature == "+aix-shared-lib-tls-model-opt") {
       HasAIXShLibTLSModelOpt = true;
+    } else if (Feature == "+longcall") {
+      UseLongCalls = true;
     }
     // TODO: Finish this list and add an assert that we've handled them
     // all.
@@ -728,6 +730,7 @@ bool PPCTargetInfo::hasFeature(StringRef Feature) const {
       .Case("isa-v31-instructions", IsISA3_1)
       .Case("quadword-atomics", HasQuadwordAtomics)
       .Case("aix-shared-lib-tls-model-opt", HasAIXShLibTLSModelOpt)
+      .Case("longcall", UseLongCalls)
       .Default(false);
 }
 

clang/lib/Basic/Targets/PPC.h

@@ -82,6 +82,7 @@ class LLVM_LIBRARY_VISIBILITY PPCTargetInfo : public TargetInfo {
   bool IsISA3_1 = false;
   bool HasQuadwordAtomics = false;
   bool HasAIXShLibTLSModelOpt = false;
+  bool UseLongCalls = false;
 
 protected:
   std::string ABI;

clang/lib/CodeGen/CGCall.cpp

@@ -26,7 +26,6 @@
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclObjC.h"
 #include "clang/Basic/CodeGenOptions.h"
-#include "clang/Basic/DiagnosticSema.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/CodeGen/CGFunctionInfo.h"
 #include "clang/CodeGen/SwiftCallingConv.h"
@@ -5752,15 +5751,8 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
   if (llvm::CallInst *Call = dyn_cast<llvm::CallInst>(CI)) {
     if (TargetDecl && TargetDecl->hasAttr<NotTailCalledAttr>())
       Call->setTailCallKind(llvm::CallInst::TCK_NoTail);
-    else if (IsMustTail) {
-      if (getTarget().getTriple().isPPC()) {
-        if (getTarget().getTriple().isOSAIX())
-          CGM.getDiags().Report(Loc, diag::err_aix_musttail_unsupported);
-        else
-          CGM.getDiags().Report(Loc, diag::warn_ppc_musttail_maybe_ignored);
-      }
+    else if (IsMustTail)
       Call->setTailCallKind(llvm::CallInst::TCK_MustTail);
-    }
   }
 
   // Add metadata for calls to MSAllocator functions

clang/lib/Sema/SemaStmt.cpp

@@ -743,6 +743,20 @@ bool Sema::checkMustTailAttr(const Stmt *St, const Attr &MTA) {
     CallerType.Func = CallerDecl->getType()->getAs<FunctionProtoType>();
   }
 
+  if (Context.getTargetInfo().getTriple().isPPC()) {
+    if (Context.getTargetInfo().getTriple().isOSAIX())
+      return Diag(St->getBeginLoc(), diag::err_aix_musttail_unsupported);
+    else if (!Context.getTargetInfo().hasFeature("pcrelative-memops")) {
+      if (Context.getTargetInfo().hasFeature("longcall"))
+        return Diag(St->getBeginLoc(), diag::err_ppc_impossible_musttail) << 0;
+      else if (!CE->getDirectCallee())
+        return Diag(St->getBeginLoc(), diag::err_ppc_impossible_musttail) << 1;
+      else if (isa_and_nonnull<FunctionDecl>(CE->getCalleeDecl()) &&
+               !cast<FunctionDecl>(CE->getCalleeDecl())->isDefined())
+        return Diag(St->getBeginLoc(), diag::err_ppc_impossible_musttail) << 2;
+    }
+  }
+
   const Expr *CalleeExpr = CE->getCallee()->IgnoreParens();
   const auto *CalleeBinOp = dyn_cast<BinaryOperator>(CalleeExpr);
   SourceLocation CalleeLoc = CE->getCalleeDecl()

clang/test/SemaCXX/attr-musttail-ppc.cpp

@@ -1,12 +1,36 @@
-// RUN: %clang_cc1 %s -triple powerpc64-ibm-aix-xcoff -o /dev/null -emit-llvm -verify=aix
-// RUN: %clang_cc1 %s -triple powerpc-ibm-aix-xcoff -o /dev/null -emit-llvm -verify=aix
-// RUN: %clang_cc1 %s -triple powerpc64-unknown-linux-gnu -o /dev/null -emit-llvm -verify=linux
-// RUN: %clang_cc1 %s -triple powerpc-unknown-linux-gnu -o /dev/null -emit-llvm -verify=linux
-// RUN: %clang_cc1 %s -triple powerpc64le-unknown-linux-gnu -o /dev/null -emit-llvm -verify=linux
+// RUN: %clang_cc1 %s -triple powerpc64-ibm-aix-xcoff -fsyntax-only -verify=aix
+// RUN: %clang_cc1 %s -triple powerpc-ibm-aix-xcoff -fsyntax-only -verify=aix
+// RUN: %clang_cc1 %s -triple powerpc64-unknown-linux-gnu -fsyntax-only -verify=linux
+// RUN: %clang_cc1 %s -triple powerpc-unknown-linux-gnu -fsyntax-only -verify=linux
+// RUN: %clang_cc1 %s -triple powerpc64le-unknown-linux-gnu -fsyntax-only -verify=linux
+// RUN: %clang_cc1 %s -triple powerpc64le-unknown-linux-gnu -target-feature +pcrelative-memops -fsyntax-only -verify=good
+// RUN: %clang_cc1 %s -triple powerpc64le-unknown-linux-gnu -target-feature +longcall -fsyntax-only -verify=longcall
+// RUN: %clang_cc1 %s -triple powerpc64le-unknown-linux-gnu -target-feature +pcrelative-memops -target-feature +longcall -fsyntax-only -verify=good
 
-int Func();
-int Func1() {
-  // linux-warning@+2 {{'musttail' attribute may be ignored on ppc targets}}
+int good_callee() {
+  return 0;
+}
+int good_caller() {
+  // good-no-diagnostics
+  // longcall-error@+2 {{'musttail' attribute for this call is impossible because long calls can not be tail called}}
+  // aix-error@+1 {{'musttail' attribute is not supported on AIX}}
+  [[clang::musttail]] return good_callee();
+}
+
+int func();
+int external_call() {
+  // good-no-diagnostics
+  // longcall-error@+3 {{'musttail' attribute for this call is impossible because long calls can not be tail called}}
+  // linux-error@+2 {{'musttail' attribute for this call is impossible because external calls can not be tail called}}
+  // aix-error@+1 {{'musttail' attribute is not supported on AIX}}
+  [[clang::musttail]] return func();
+}
+
+void indirect_call(int r) {
+  auto Fn = (void (*)(int))1;
+  // good-no-diagnostics
+  // longcall-error@+3 {{'musttail' attribute for this call is impossible because long calls can not be tail called}}
+  // linux-error@+2 {{'musttail' attribute for this call is impossible because indirect calls can not be tail called}}
   // aix-error@+1 {{'musttail' attribute is not supported on AIX}}
-  [[clang::musttail]] return Func();
+  [[clang::musttail]] return Fn(r);
 }

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

@@ -146,10 +146,6 @@ static cl::opt<unsigned> PPCAIXTLSModelOptUseIEForLDLimit(
     cl::desc("Set inclusive limit count of TLS local-dynamic access(es) in a "
              "function to use initial-exec"));
 
-static cl::opt<bool> AbortOnImpossibleMusttailCall(
-    "ppc-abort-on-impossible-musttailcall", cl::init(false), cl::Hidden,
-    cl::desc("Abort if any call marked as musttail is impossible."));
-
 STATISTIC(NumTailCalls, "Number of tail calls");
 STATISTIC(NumSiblingCalls, "Number of sibling calls");
 STATISTIC(ShufflesHandledWithVPERM,
@@ -5949,14 +5945,9 @@ PPCTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
     }
   }
 
-  if (!isTailCall && CB && CB->isMustTailCall()) {
-    if (AbortOnImpossibleMusttailCall)
-      report_fatal_error("failed to perform tail call elimination on a call "
-                         "site marked musttail");
-    else
-      cast<CallInst>(const_cast<CallBase *>(CB))
-          ->setTailCallKind(llvm::CallInst::TCK_Tail);
-  }
+  if (!isTailCall && CB && CB->isMustTailCall())
+    report_fatal_error("failed to perform tail call elimination on a call "
+                       "site marked musttail");
 
   // When long calls (i.e. indirect calls) are always used, calls are always
   // made via function pointer. If we have a function name, first translate it