[PATCH] D12547: Add support for function attribute "disable_tail_calls"

[Akira Hatanaka via cfe-commits]

ahatanak created this revision.
ahatanak added a subscriber: cfe-commits.

There have been requests for a function attribute that disables tail call optimizations in the backend. This patch defines such an attribute.

http://reviews.llvm.org/D12547

Files:
  include/clang/Basic/Attr.td
  lib/CodeGen/CGCall.cpp
  lib/Sema/SemaDeclAttr.cpp
  test/CodeGen/attr-disable-tail-calls.c

Index: test/CodeGen/attr-disable-tail-calls.c
===================================================================
--- test/CodeGen/attr-disable-tail-calls.c
+++ test/CodeGen/attr-disable-tail-calls.c
@@ -1,11 +1,19 @@
-// RUN: %clang_cc1 -triple x86_64-apple-macosx10.7.0 %s -emit-llvm -mdisable-tail-calls -o - | FileCheck %s -check-prefix=CHECK -check-prefix=DISABLE
-// RUN: %clang_cc1 -triple x86_64-apple-macosx10.7.0 %s -emit-llvm -o - | FileCheck %s -check-prefix=CHECK -check-prefix=ENABLE
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.7.0 %s -emit-llvm -mdisable-tail-calls -o - | FileCheck %s -check-prefix=DISABLE
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.7.0 %s -emit-llvm -o - | FileCheck %s -check-prefix=ENABLE
 
-// CHECK: define i32 @f1() [[ATTR:#[0-9]+]] {
+// DISABLE: define i32 @f1() [[ATTRTRUE:#[0-9]+]] {
+// DISABLE: define i32 @f2() [[ATTRTRUE]] {
+// ENABLE: define i32 @f1() [[ATTRFALSE:#[0-9]+]] {
+// ENABLE: define i32 @f2() [[ATTRTRUE:#[0-9]+]] {
 
 int f1() {
   return 0;
 }
 
-// DISABLE: attributes [[ATTR]] = { {{.*}} "disable-tail-calls"="true" {{.*}} }
-// ENABLE: attributes [[ATTR]] = { {{.*}} "disable-tail-calls"="false" {{.*}} }
+int f2() __attribute__((disable_tail_calls)) {
+  return 0;
+}
+
+// DISABLE: attributes [[ATTRTRUE]] = { {{.*}} "disable-tail-calls"="true" {{.*}} }
+// ENABLE: attributes [[ATTRFALSE]] = { {{.*}} "disable-tail-calls"="false" {{.*}} }
+// ENABLE: attributes [[ATTRTRUE]] = { {{.*}} "disable-tail-calls"="true" {{.*}} }
Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -4878,6 +4878,9 @@
   case AttributeList::AT_ReturnsTwice:
     handleSimpleAttribute<ReturnsTwiceAttr>(S, D, Attr);
     break;
+  case AttributeList::AT_DisableTailCalls:
+    handleSimpleAttribute<DisableTailCallsAttr>(S, D, Attr);
+    break;
   case AttributeList::AT_Used:
     handleUsedAttr(S, D, Attr);
     break;
Index: lib/CodeGen/CGCall.cpp
===================================================================
--- lib/CodeGen/CGCall.cpp
+++ lib/CodeGen/CGCall.cpp
@@ -1474,8 +1474,12 @@
       FuncAttrs.addAttribute("no-frame-pointer-elim-non-leaf");
     }
 
-    FuncAttrs.addAttribute("disable-tail-calls",
-                           llvm::toStringRef(CodeGenOpts.DisableTailCalls));
+    if ((TargetDecl && TargetDecl->hasAttr<DisableTailCallsAttr>()) ||
+        CodeGenOpts.DisableTailCalls)
+      FuncAttrs.addAttribute("disable-tail-calls", "true");
+    else
+      FuncAttrs.addAttribute("disable-tail-calls", "false");
+
     FuncAttrs.addAttribute("less-precise-fpmad",
                            llvm::toStringRef(CodeGenOpts.LessPreciseFPMAD));
     FuncAttrs.addAttribute("no-infs-fp-math",
Index: include/clang/Basic/Attr.td
===================================================================
--- include/clang/Basic/Attr.td
+++ include/clang/Basic/Attr.td
@@ -891,6 +891,12 @@
   let Documentation = [Undocumented];
 }
 
+def DisableTailCalls : InheritableAttr {
+  let Spellings = [GNU<"disable_tail_calls">];
+  let Subjects = SubjectList<[Function]>;
+  let Documentation = [Undocumented];
+}
+
 def NoAlias : InheritableAttr {
   let Spellings = [Declspec<"noalias">];
   let Subjects = SubjectList<[Function]>;


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