<div class="doc_text">
<p>The NoAlias response is used when the two pointers refer to distinct objects,
-regardless of whether the pointers compare equal. For example, freed pointers
-don't alias any pointers that were allocated afterwards. As a degenerate case,
-pointers returned by malloc(0) have no bytes for an object, and are considered
-NoAlias even when malloc returns the same pointer. The same rule applies to
-NULL pointers.</p>
+even regardless of whether the pointers compare equal. For example, freed
+pointers don't alias any pointers that were allocated afterwards. As a
+degenerate case, pointers returned by malloc(0) have no bytes for an object,
+and are considered NoAlias even when malloc returns the same pointer. The same
+rule applies to NULL pointers.</p>
<p>The MayAlias response is used whenever the two pointers might refer to the
same object. If the two memory objects overlap, but do not start at the same
parameter. The caller is responsible for ensuring that this is the
case. On a function return value, <tt>noalias</tt> additionally indicates
that the pointer does not alias any other pointers visible to the
- caller. For further details, please see the discussion of the NoAlias
- response in
- <a href="http://llvm.org/docs/AliasAnalysis.html#MustMayNo">alias
- analysis</a>.</dd>
-
- <dt><tt>nocapture</tt></dt>
- <dd>This indicates that the callee does not make any copies of the pointer
- that outlive the callee itself. This is not a valid attribute for return
- values.</dd>
+ caller. Note that this applies only to pointers that can be used to actually
+ load/store a value: NULL, unique pointers from malloc(0), and freed pointers
+ are considered to not alias anything.</dd>
<dt><tt>nest</tt></dt>
<dd>This indicates that the pointer parameter can be excised using the
#ifndef LLVM_ATTRIBUTES_H
#define LLVM_ATTRIBUTES_H
-#include "llvm/Support/MathExtras.h"
#include <cassert>
#include <string>
/// Attributes - A bitset of attributes.
typedef unsigned Attributes;
-
+
namespace Attribute {
/// Function parameters and results can have attributes to indicate how they
const Attributes Nest = 1<<8; ///< Nested function static chain
const Attributes ReadNone = 1<<9; ///< Function does not access memory
const Attributes ReadOnly = 1<<10; ///< Function only reads from memory
-const Attributes NoInline = 1<<11; ///< inline=never
-const Attributes AlwaysInline = 1<<12; ///< inline=always
-const Attributes OptimizeForSize = 1<<13; ///< opt_size
-const Attributes StackProtect = 1<<14; ///< Stack protection.
-const Attributes StackProtectReq = 1<<15; ///< Stack protection required.
-const Attributes Alignment = 31<<16; ///< Alignment of parameter (5 bits)
- // stored as log2 of alignment with +1 bias
- // 0 means unaligned different from align 1
-const Attributes NoCapture = 1<<21; ///< Function creates no aliases of pointer
-
+const Attributes NoInline = 1<<11; // inline=never
+const Attributes AlwaysInline = 1<<12; // inline=always
+const Attributes OptimizeForSize = 1<<13; // opt_size
+const Attributes StackProtect = 1<<14; // Stack protection.
+const Attributes StackProtectReq = 1<<15; // Stack protection required.
+const Attributes Alignment = 0xffff<<16; ///< Alignment of parameter (16 bits)
+ // 0 = unknown, else in clear (not log)
+
/// @brief Attributes that only apply to function parameters.
-const Attributes ParameterOnly = ByVal | Nest | StructRet | NoCapture;
+const Attributes ParameterOnly = ByVal | Nest | StructRet;
/// @brief Attributes that only apply to function.
const Attributes FunctionOnly = NoReturn | NoUnwind | ReadNone | ReadOnly |
/// @brief Attributes that are mutually incompatible.
const Attributes MutuallyIncompatible[4] = {
- ByVal | InReg | Nest | StructRet,
+ ByVal | InReg | Nest | StructRet,
ZExt | SExt,
ReadNone | ReadOnly,
NoInline | AlwaysInline
/// This turns an int alignment (a power of 2, normally) into the
/// form used internally in Attributes.
inline Attributes constructAlignmentFromInt(unsigned i) {
- assert(isPowerOf2_32(i) && "Alignment must be a power of two.");
- assert(i <= 0x40000000 && "Alignment too large.");
- return (Log2_32(i)+1) << 16;
+ return (i << 16);
}
/// The set of Attributes set in Attributes is converted to a
/// getParamAlignment - Return the alignment for the specified function
/// parameter.
unsigned getParamAlignment(unsigned Idx) const {
- return 1ull << (((getAttributes(Idx) & Attribute::Alignment) >> 16) - 1);
+ return (getAttributes(Idx) & Attribute::Alignment) >> 16;
}
/// hasAttrSomewhere - Return true if the specified attribute is set for at
// callees could modify it.
break; // next use
case Instruction::Call:
- // If the argument to the call has the nocapture attribute, then the call
- // may store or load to the pointer, but it cannot escape.
- if (cast<CallInst>(I)->paramHasAttr(UI.getOperandNo(),
- Attribute::NoCapture))
- continue;
-
- // FIXME: MemIntrinsics should have their operands marked nocapture!
- if (isa<MemIntrinsic>(I))
- continue; // next use
- return true;
- case Instruction::Invoke:
- // If the argument to the call has the nocapture attribute, then the call
- // may store or load to the pointer, but it cannot escape.
- if (cast<InvokeInst>(I)->paramHasAttr(UI.getOperandNo()-2,
- Attribute::NoCapture))
- continue;
- return true;
+ // If the call is to a few known safe intrinsics, we know that it does
+ // not escape.
+ // TODO: Eventually just check the 'nocapture' attribute.
+ if (!isa<MemIntrinsic>(I))
+ return true;
+ break; // next use
default:
return true;
}
KEYWORD("nounwind", NOUNWIND);
KEYWORD("noreturn", NORETURN);
KEYWORD("noalias", NOALIAS);
- KEYWORD("nocapture", NOCAPTURE);
KEYWORD("byval", BYVAL);
KEYWORD("nest", NEST);
KEYWORD("readnone", READNONE);
%token <OtherOpVal> EXTRACTVALUE INSERTVALUE
// Function Attributes
-%token SIGNEXT ZEROEXT NORETURN INREG SRET NOUNWIND NOALIAS NOCAPTURE BYVAL
-%token READNONE READONLY GC OPTSIZE NOINLINE ALWAYSINLINE SSP SSPREQ NEST
+%token SIGNEXT ZEROEXT NORETURN INREG SRET NOUNWIND NOALIAS BYVAL NEST
+%token READNONE READONLY GC OPTSIZE NOINLINE ALWAYSINLINE SSP SSPREQ
// Visibility Styles
%token DEFAULT HIDDEN PROTECTED
CHECK_FOR_ERROR
};
-Attribute : ZEROEXT { $$ = Attribute::ZExt; }
- | ZEXT { $$ = Attribute::ZExt; }
- | SIGNEXT { $$ = Attribute::SExt; }
- | SEXT { $$ = Attribute::SExt; }
- | INREG { $$ = Attribute::InReg; }
- | SRET { $$ = Attribute::StructRet; }
- | NOALIAS { $$ = Attribute::NoAlias; }
- | NOCAPTURE { $$ = Attribute::NoCapture; }
- | BYVAL { $$ = Attribute::ByVal; }
- | NEST { $$ = Attribute::Nest; }
+Attribute : ZEROEXT { $$ = Attribute::ZExt; }
+ | ZEXT { $$ = Attribute::ZExt; }
+ | SIGNEXT { $$ = Attribute::SExt; }
+ | SEXT { $$ = Attribute::SExt; }
+ | INREG { $$ = Attribute::InReg; }
+ | SRET { $$ = Attribute::StructRet; }
+ | NOALIAS { $$ = Attribute::NoAlias; }
+ | BYVAL { $$ = Attribute::ByVal; }
+ | NEST { $$ = Attribute::Nest; }
| ALIGN EUINT64VAL { $$ =
Attribute::constructAlignmentFromInt($2); }
;
$$ = $2;
if ($$ != 0 && !isPowerOf2_32($$))
GEN_ERROR("Alignment must be a power of two");
- if ($$ > 0x40000000)
- GEN_ERROR("Alignment too large");
CHECK_FOR_ERROR
};
OptCAlign : /*empty*/ { $$ = 0; } |
$$ = $3;
if ($$ != 0 && !isPowerOf2_32($$))
GEN_ERROR("Alignment must be a power of two");
- if ($$ > 0x40000000)
- GEN_ERROR("Alignment too large");
CHECK_FOR_ERROR
};
| ALIGN EUINT64VAL {
if ($2 != 0 && !isPowerOf2_32($2))
GEN_ERROR("Alignment must be a power of two");
- if ($2 > 0x40000000)
- GEN_ERROR("Alignment too large");
CurGV->setAlignment($2);
CHECK_FOR_ERROR
};
Attributes RetAttribute = Attribute::None;
Attributes FnAttribute = Attribute::None;
for (unsigned i = 0, e = Record.size(); i != e; i += 2) {
- // FIXME: remove in LLVM 3.0
- // The alignment is stored as a 16-bit raw value from bits 31--16.
- // We shift the bits above 31 down by 11 bits.
-
- unsigned Alignment = (Record[i+1] & (0xffffull << 16)) >> 16;
- if (Alignment && !isPowerOf2_32(Alignment))
- return Error("Alignment is not a power of two.");
-
- Attributes ReconstitutedAttr = Record[i+1] & 0xffff;
- if (Alignment)
- ReconstitutedAttr |= Attribute::constructAlignmentFromInt(Alignment);
- ReconstitutedAttr |= (Record[i+1] & (0xffffull << 32)) >> 11;
- Record[i+1] = ReconstitutedAttr;
-
if (Record[i] == 0)
RetAttribute = Record[i+1];
else if (Record[i] == ~0U)
for (unsigned i = 0, e = A.getNumSlots(); i != e; ++i) {
const AttributeWithIndex &PAWI = A.getSlot(i);
Record.push_back(PAWI.Index);
-
- // FIXME: remove in LLVM 3.0
- // Store the alignment in the bitcode as a 16-bit raw value instead of a
- // 5-bit log2 encoded value. Shift the bits above the alignment up by
- // 11 bits.
- uint64_t FauxAttr = PAWI.Attrs & 0xffff;
- if (PAWI.Attrs & Attribute::Alignment)
- FauxAttr |= (1ull<<16)<<(((PAWI.Attrs & Attribute::Alignment)-1) >> 16);
- FauxAttr |= (PAWI.Attrs & (0x3FFull << 21)) << 11;
-
- Record.push_back(FauxAttr);
+ Record.push_back(PAWI.Attrs);
}
Stream.EmitRecord(bitc::PARAMATTR_CODE_ENTRY, Record);
Result += "inreg ";
if (Attrs & Attribute::NoAlias)
Result += "noalias ";
- if (Attrs & Attribute::NoCapture)
- Result += "nocapture ";
if (Attrs & Attribute::StructRet)
Result += "sret ";
if (Attrs & Attribute::ByVal)
Result += "sspreq ";
if (Attrs & Attribute::Alignment) {
Result += "align ";
- Result += utostr(1ull << (((Attrs & Attribute::Alignment)>>16) - 1));
+ Result += utostr((Attrs & Attribute::Alignment) >> 16);
Result += " ";
}
// Trim the trailing space.
- assert(!Result.empty() && "Unknown attribute!");
Result.erase(Result.end()-1);
return Result;
}
if (!isa<PointerType>(Ty))
// Attributes that only apply to pointers.
- Incompatible |= ByVal | Nest | NoAlias | StructRet | NoCapture;
+ Incompatible |= ByVal | Nest | NoAlias | StructRet;
return Incompatible;
}
-; RUN: llvm-as < %s | opt -basicaa -gvn -instcombine | llvm-dis | grep {ret i32 0}
-
-declare i32* @test(i32* nocapture)
-
-define i32 @test2() {
- %P = alloca i32
- %Q = call i32* @test(i32* %P)
- %a = load i32* %P
- store i32 4, i32* %Q ;; cannot clobber P since it is nocapture.
- %b = load i32* %P
- %c = sub i32 %a, %b
- ret i32 %c
-}
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