Add 'nonnull', a new parameter and return attribute which indicates that the pointer is not null. Instcombine will elide comparisons between these and null. Patch by Luqman Aden!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209185 91177308-0d34-0410-b5e6-96231b3b80d8

docs/LangRef.rst

@@ -847,6 +847,13 @@ Currently, only the following parameter attributes are defined:
     operands for the :ref:`bitcast instruction <i_bitcast>`. This is not a
     valid attribute for return values and can only be applied to one parameter.
 
+``nonnull``
+    This indicates that the parameter or return pointer is not null. This
+    attribute may only be applied to pointer typed parameters. This is not
+    checked or enforced by LLVM, the caller must ensure that the pointer
+    passed in is non-null, or the callee must ensure that the returned pointer 
+    is non-null.
+
 .. _gc:
 
 Garbage Collector Names

include/llvm-c/Core.h

@@ -165,7 +165,8 @@ typedef enum {
     LLVMStackProtectStrongAttribute = 1ULL<<33,
     LLVMCold = 1ULL << 34,
     LLVMOptimizeNone = 1ULL << 35,
-    LLVMInAllocaAttribute = 1ULL << 36
+    LLVMInAllocaAttribute = 1ULL << 36,
+    LLVMNonNullAttribute = 1ULL << 37
     */
 } LLVMAttribute;
 

include/llvm/Bitcode/LLVMBitCodes.h

@@ -371,7 +371,8 @@ namespace bitc {
     ATTR_KIND_BUILTIN = 35,
     ATTR_KIND_COLD = 36,
     ATTR_KIND_OPTIMIZE_NONE = 37,
-    ATTR_KIND_IN_ALLOCA = 38
+    ATTR_KIND_IN_ALLOCA = 38,
+    ATTR_KIND_NON_NULL = 39
   };
 
 } // End bitc namespace

include/llvm/IR/Argument.h

@@ -55,6 +55,10 @@ public:
   /// For example in "void foo(int a, float b)" a is 0 and b is 1.
   unsigned getArgNo() const;
 
+  /// \brief Return true if this argument has the nonnull attribute on it in
+  /// its containing function.
+  bool hasNonNullAttr() const;
+
   /// \brief Return true if this argument has the byval attribute on it in its
   /// containing function.
   bool hasByValAttr() const;

include/llvm/IR/Attributes.h

@@ -86,6 +86,7 @@ public:
     NoInline,              ///< inline=never
     NonLazyBind,           ///< Function is called early and/or
                            ///< often, so lazy binding isn't worthwhile
+    NonNull,               ///< Pointer is known to be not null
     NoRedZone,             ///< Disable redzone
     NoReturn,              ///< Mark the function as not returning
     NoUnwind,              ///< Function doesn't unwind stack

lib/Analysis/ValueTracking.cpp

@@ -2065,9 +2065,9 @@ bool llvm::isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI) {
   // Alloca never returns null, malloc might.
   if (isa<AllocaInst>(V)) return true;
 
-  // A byval or inalloca argument is never null.
+  // A byval, inalloca, or nonnull argument is never null.
   if (const Argument *A = dyn_cast<Argument>(V))
-    return A->hasByValOrInAllocaAttr();
+    return A->hasByValOrInAllocaAttr() || A->hasNonNullAttr();
 
   // Global values are not null unless extern weak.
   if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))

lib/AsmParser/LLLexer.cpp

@@ -593,6 +593,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(noimplicitfloat);
   KEYWORD(noinline);
   KEYWORD(nonlazybind);
+  KEYWORD(nonnull);
   KEYWORD(noredzone);
   KEYWORD(noreturn);
   KEYWORD(nounwind);

lib/AsmParser/LLParser.cpp

@@ -1003,6 +1003,7 @@ bool LLParser::ParseFnAttributeValuePairs(AttrBuilder &B,
     case lltok::kw_nest:
     case lltok::kw_noalias:
     case lltok::kw_nocapture:
+    case lltok::kw_nonnull:
     case lltok::kw_returned:
     case lltok::kw_sret:
       HaveError |=
@@ -1217,6 +1218,7 @@ bool LLParser::ParseOptionalParamAttrs(AttrBuilder &B) {
     case lltok::kw_nest:            B.addAttribute(Attribute::Nest); break;
     case lltok::kw_noalias:         B.addAttribute(Attribute::NoAlias); break;
     case lltok::kw_nocapture:       B.addAttribute(Attribute::NoCapture); break;
+    case lltok::kw_nonnull:         B.addAttribute(Attribute::NonNull); break;
     case lltok::kw_readnone:        B.addAttribute(Attribute::ReadNone); break;
     case lltok::kw_readonly:        B.addAttribute(Attribute::ReadOnly); break;
     case lltok::kw_returned:        B.addAttribute(Attribute::Returned); break;
@@ -1269,6 +1271,7 @@ bool LLParser::ParseOptionalReturnAttrs(AttrBuilder &B) {
       return HaveError;
     case lltok::kw_inreg:           B.addAttribute(Attribute::InReg); break;
     case lltok::kw_noalias:         B.addAttribute(Attribute::NoAlias); break;
+    case lltok::kw_nonnull:         B.addAttribute(Attribute::NonNull); break;
     case lltok::kw_signext:         B.addAttribute(Attribute::SExt); break;
     case lltok::kw_zeroext:         B.addAttribute(Attribute::ZExt); break;
 

lib/AsmParser/LLToken.h

@@ -117,6 +117,7 @@ namespace lltok {
     kw_noimplicitfloat,
     kw_noinline,
     kw_nonlazybind,
+    kw_nonnull,
     kw_noredzone,
     kw_noreturn,
     kw_nounwind,

lib/Bitcode/Reader/BitcodeReader.cpp

@@ -569,6 +569,8 @@ static Attribute::AttrKind GetAttrFromCode(uint64_t Code) {
     return Attribute::NoInline;
   case bitc::ATTR_KIND_NON_LAZY_BIND:
     return Attribute::NonLazyBind;
+  case bitc::ATTR_KIND_NON_NULL:
+    return Attribute::NonNull;
   case bitc::ATTR_KIND_NO_RED_ZONE:
     return Attribute::NoRedZone;
   case bitc::ATTR_KIND_NO_RETURN:

lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -197,6 +197,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_NO_INLINE;
   case Attribute::NonLazyBind:
     return bitc::ATTR_KIND_NON_LAZY_BIND;
+  case Attribute::NonNull:
+    return bitc::ATTR_KIND_NON_NULL;
   case Attribute::NoRedZone:
     return bitc::ATTR_KIND_NO_RED_ZONE;
   case Attribute::NoReturn:

lib/IR/Attributes.cpp

@@ -193,6 +193,8 @@ std::string Attribute::getAsString(bool InAttrGrp) const {
     return "noinline";
   if (hasAttribute(Attribute::NonLazyBind))
     return "nonlazybind";
+  if (hasAttribute(Attribute::NonNull))
+    return "nonnull";
   if (hasAttribute(Attribute::NoRedZone))
     return "noredzone";
   if (hasAttribute(Attribute::NoReturn))
@@ -392,6 +394,7 @@ uint64_t AttributeImpl::getAttrMask(Attribute::AttrKind Val) {
   case Attribute::Builtin:         return 1ULL << 41;
   case Attribute::OptimizeNone:    return 1ULL << 42;
   case Attribute::InAlloca:        return 1ULL << 43;
+  case Attribute::NonNull:         return 1ULL << 44;
   }
   llvm_unreachable("Unsupported attribute type");
 }
@@ -1177,6 +1180,7 @@ AttributeSet AttributeFuncs::typeIncompatible(Type *Ty, uint64_t Index) {
       .addAttribute(Attribute::Nest)
       .addAttribute(Attribute::NoAlias)
       .addAttribute(Attribute::NoCapture)
+      .addAttribute(Attribute::NonNull)
       .addAttribute(Attribute::ReadNone)
       .addAttribute(Attribute::ReadOnly)
       .addAttribute(Attribute::StructRet)

lib/IR/Function.cpp

@@ -76,6 +76,14 @@ unsigned Argument::getArgNo() const {
   return ArgIdx;
 }
 
+/// hasNonNullAttr - Return true if this argument has the nonnull attribute on
+/// it in its containing function.
+bool Argument::hasNonNullAttr() const {
+  if (!getType()->isPointerTy()) return false;
+  return getParent()->getAttributes().
+    hasAttribute(getArgNo()+1, Attribute::NonNull);
+}
+
 /// hasByValAttr - Return true if this argument has the byval attribute on it
 /// in its containing function.
 bool Argument::hasByValAttr() const {

test/Bitcode/attributes.ll

@@ -218,6 +218,11 @@ define void @f36(i8* inalloca) {
         ret void
 }
 
+define nonnull i8* @f37(i8* nonnull %a) {
+; CHECK: define nonnull i8* @f37(i8* nonnull %a) {
+        ret i8* %a
+}
+
 ; CHECK: attributes #0 = { noreturn }
 ; CHECK: attributes #1 = { nounwind }
 ; CHECK: attributes #2 = { readnone }