[Attr] Add "willreturn" function attribute

This patch introduces a new function attribute, willreturn, to indicate
that a call of this function will either exhibit undefined behavior or
comes back and continues execution at a point in the existing call stack
that includes the current invocation.

This attribute guarantees that the function does not have any endless
loops, endless recursion, or terminating functions like abort or exit.

Patch by Hideto Ueno (@uenoku)

Reviewers: jdoerfert

Subscribers: mehdi_amini, hiraditya, steven_wu, dexonsmith, lebedev.ri, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D62801

llvm-svn: 364555

8 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/AsmParser/LLLexer.cpp b/llvm/lib/AsmParser/LLLexer.cpp
index dc8ff7f1315..1f34025b660 100644
--- a/llvm/lib/AsmParser/LLLexer.cpp
+++ b/llvm/lib/AsmParser/LLLexer.cpp
@@ -683,6 +683,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(swifterror);
   KEYWORD(swiftself);
   KEYWORD(uwtable);
+  KEYWORD(willreturn);
   KEYWORD(writeonly);
   KEYWORD(zeroext);
   KEYWORD(immarg);
diff --git a/llvm/lib/AsmParser/LLParser.cpp b/llvm/lib/AsmParser/LLParser.cpp
index b6f982bc3fb..2bd43478506 100644
--- a/llvm/lib/AsmParser/LLParser.cpp
+++ b/llvm/lib/AsmParser/LLParser.cpp
@@ -1315,6 +1315,7 @@ bool LLParser::ParseFnAttributeValuePairs(AttrBuilder &B,
       break;
     case lltok::kw_strictfp: B.addAttribute(Attribute::StrictFP); break;
     case lltok::kw_uwtable: B.addAttribute(Attribute::UWTable); break;
+    case lltok::kw_willreturn: B.addAttribute(Attribute::WillReturn); break;
     case lltok::kw_writeonly: B.addAttribute(Attribute::WriteOnly); break;
 
     // Error handling.
diff --git a/llvm/lib/AsmParser/LLToken.h b/llvm/lib/AsmParser/LLToken.h
index a1e70932178..f276a39037f 100644
--- a/llvm/lib/AsmParser/LLToken.h
+++ b/llvm/lib/AsmParser/LLToken.h
@@ -225,6 +225,7 @@ enum Kind {
   kw_swifterror,
   kw_swiftself,
   kw_uwtable,
+  kw_willreturn,
   kw_writeonly,
   kw_zeroext,
   kw_immarg,
diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 4c346176bec..4d004dcb735 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1272,6 +1272,8 @@ static uint64_t getRawAttributeMask(Attribute::AttrKind Val) {
     return 1ULL << 60;
   case Attribute::ImmArg:
     return 1ULL << 61;
+  case Attribute::WillReturn:
+    return 1ULL << 62;
   case Attribute::Dereferenceable:
     llvm_unreachable("dereferenceable attribute not supported in raw format");
     break;
@@ -1510,6 +1512,8 @@ static Attribute::AttrKind getAttrFromCode(uint64_t Code) {
     return Attribute::SwiftSelf;
   case bitc::ATTR_KIND_UW_TABLE:
     return Attribute::UWTable;
+  case bitc::ATTR_KIND_WILLRETURN:
+    return Attribute::WillReturn;
   case bitc::ATTR_KIND_WRITEONLY:
     return Attribute::WriteOnly;
   case bitc::ATTR_KIND_Z_EXT:
diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index 1f39fa34a8b..33dbbea5f8c 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -710,6 +710,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_SWIFT_SELF;
   case Attribute::UWTable:
     return bitc::ATTR_KIND_UW_TABLE;
+  case Attribute::WillReturn:
+    return bitc::ATTR_KIND_WILLRETURN;
   case Attribute::WriteOnly:
     return bitc::ATTR_KIND_WRITEONLY;
   case Attribute::ZExt:
diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp
index 67d35def9ff..99fc447c5af 100644
--- a/llvm/lib/IR/Attributes.cpp
+++ b/llvm/lib/IR/Attributes.cpp
@@ -333,6 +333,8 @@ std::string Attribute::getAsString(bool InAttrGrp) const {
     return "noredzone";
   if (hasAttribute(Attribute::NoReturn))
     return "noreturn";
+  if (hasAttribute(Attribute::WillReturn))
+    return "willreturn";
   if (hasAttribute(Attribute::NoCfCheck))
     return "nocf_check";
   if (hasAttribute(Attribute::NoRecurse))
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 0deb0367b42..0ab421e057d 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -1486,6 +1486,7 @@ void Verifier::visitModuleFlagCGProfileEntry(const MDOperand &MDO) {
 static bool isFuncOnlyAttr(Attribute::AttrKind Kind) {
   switch (Kind) {
   case Attribute::NoReturn:
+  case Attribute::WillReturn:
   case Attribute::NoCfCheck:
   case Attribute::NoUnwind:
   case Attribute::NoInline:
diff --git a/llvm/lib/Transforms/Utils/CodeExtractor.cpp b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
index 61c1e9313c2..23a404c11a6 100644
--- a/llvm/lib/Transforms/Utils/CodeExtractor.cpp
+++ b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
@@ -801,6 +801,7 @@ Function *CodeExtractor::constructFunction(const ValueSet &inputs,
       case Attribute::StructRet:
       case Attribute::SwiftError:
       case Attribute::SwiftSelf:
+      case Attribute::WillReturn:
       case Attribute::WriteOnly:
       case Attribute::ZExt:
       case Attribute::ImmArg: