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Change packed struct layout so that field sizes

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are the same as in unpacked structs, only field
positions differ.  This only matters for structs
containing x86 long double or an apint; it may
cause backwards compatibility problems if someone
has bitcode containing a packed struct with a
field of one of those types.
The issue is that only 10 bytes are needed to
hold an x86 long double: the store size is 10
bytes, but the ABI size is 12 or 16 bytes (linux/
darwin) which comes from rounding the store size
up by the alignment.  Because it seemed silly not
to pack an x86 long double into 10 bytes in a
packed struct, this is what was done.  I now
think this was a mistake.  Reserving the ABI size
for an x86 long double field even in a packed
struct makes things more uniform: the ABI size is
now always used when reserving space for a type.
This means that developers are less likely to
make mistakes.  It also makes life easier for the
CBE which otherwise could not represent all LLVM
packed structs (PR2402).
Front-end people might need to adjust the way
they create LLVM structs - see following change
to llvm-gcc.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51928 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2008-06-04 08:21:45 +00:00
parent 32a9e7a265
commit a0fcc08e65
5 changed files with 29 additions and 23 deletions
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3
include/llvm/CodeGen/AsmPrinter.h
View File

@ -314,8 +314,7 @@ namespace llvm {
void EmitConstantValueOnly(const Constant *CV);
/// EmitGlobalConstant - Print a general LLVM constant to the .s file.
/// If Packed is false, pad to the ABI size.
void EmitGlobalConstant(const Constant* CV, bool Packed = false);
void EmitGlobalConstant(const Constant* CV);
virtual void EmitMachineConstantPoolValue(MachineConstantPoolValue *MCPV);

16
lib/CodeGen/AsmPrinter.cpp
View File

@ -889,11 +889,9 @@ void AsmPrinter::EmitString(const ConstantArray *CVA) const {
}
/// EmitGlobalConstant - Print a general LLVM constant to the .s file.
/// If Packed is false, pad to the ABI size.
void AsmPrinter::EmitGlobalConstant(const Constant *CV, bool Packed) {
void AsmPrinter::EmitGlobalConstant(const Constant *CV) {
const TargetData *TD = TM.getTargetData();
unsigned Size = Packed ?
TD->getTypeStoreSize(CV->getType()) : TD->getABITypeSize(CV->getType());
unsigned Size = TD->getABITypeSize(CV->getType());
if (CV->isNullValue() || isa<UndefValue>(CV)) {
EmitZeros(Size);
@ -903,7 +901,7 @@ void AsmPrinter::EmitGlobalConstant(const Constant *CV, bool Packed) {
EmitString(CVA);
} else { // Not a string. Print the values in successive locations
for (unsigned i = 0, e = CVA->getNumOperands(); i != e; ++i)
EmitGlobalConstant(CVA->getOperand(i), false);
EmitGlobalConstant(CVA->getOperand(i));
}
return;
} else if (const ConstantStruct *CVS = dyn_cast<ConstantStruct>(CV)) {
@ -914,13 +912,13 @@ void AsmPrinter::EmitGlobalConstant(const Constant *CV, bool Packed) {
const Constant* field = CVS->getOperand(i);
// Check if padding is needed and insert one or more 0s.
uint64_t fieldSize = TD->getTypeStoreSize(field->getType());
uint64_t fieldSize = TD->getABITypeSize(field->getType());
uint64_t padSize = ((i == e-1 ? Size : cvsLayout->getElementOffset(i+1))
- cvsLayout->getElementOffset(i)) - fieldSize;
sizeSoFar += fieldSize + padSize;
// Now print the actual field value without ABI size padding.
EmitGlobalConstant(field, true);
// Now print the actual field value.
EmitGlobalConstant(field);
// Insert padding - this may include padding to increase the size of the
// current field up to the ABI size (if the struct is not packed) as well
@ -1066,7 +1064,7 @@ void AsmPrinter::EmitGlobalConstant(const Constant *CV, bool Packed) {
const VectorType *PTy = CP->getType();
for (unsigned I = 0, E = PTy->getNumElements(); I < E; ++I)
EmitGlobalConstant(CP->getOperand(I), false);
EmitGlobalConstant(CP->getOperand(I));
return;
}

7
lib/Target/TargetData.cpp
View File

@ -48,10 +48,7 @@ StructLayout::StructLayout(const StructType *ST, const TargetData &TD) {
// Loop over each of the elements, placing them in memory...
for (unsigned i = 0, e = NumElements; i != e; ++i) {
const Type *Ty = ST->getElementType(i);
unsigned TyAlign = ST->isPacked() ?
1 : TD.getABITypeAlignment(Ty);
uint64_t TySize = ST->isPacked() ?
TD.getTypeStoreSize(Ty) : TD.getABITypeSize(Ty);
unsigned TyAlign = ST->isPacked() ? 1 : TD.getABITypeAlignment(Ty);
// Add padding if necessary to align the data element properly...
StructSize = (StructSize + TyAlign - 1)/TyAlign * TyAlign;
@ -60,7 +57,7 @@ StructLayout::StructLayout(const StructType *ST, const TargetData &TD) {
StructAlignment = std::max(TyAlign, StructAlignment);
MemberOffsets[i] = StructSize;
StructSize += TySize; // Consume space for this data item
StructSize += TD.getABITypeSize(Ty); // Consume space for this data item
}
// Empty structures have alignment of 1 byte.

12
lib/Transforms/Scalar/ScalarReplAggregates.cpp
View File

@ -737,8 +737,7 @@ void SROA::RewriteBitCastUserOfAlloca(Instruction *BCInst, AllocationInst *AI,
/// HasPadding - Return true if the specified type has any structure or
/// alignment padding, false otherwise.
static bool HasPadding(const Type *Ty, const TargetData &TD,
bool inPacked = false) {
static bool HasPadding(const Type *Ty, const TargetData &TD) {
if (const StructType *STy = dyn_cast<StructType>(Ty)) {
const StructLayout *SL = TD.getStructLayout(STy);
unsigned PrevFieldBitOffset = 0;
@ -746,7 +745,7 @@ static bool HasPadding(const Type *Ty, const TargetData &TD,
unsigned FieldBitOffset = SL->getElementOffsetInBits(i);
// Padding in sub-elements?
if (HasPadding(STy->getElementType(i), TD, STy->isPacked()))
if (HasPadding(STy->getElementType(i), TD))
return true;
// Check to see if there is any padding between this element and the
@ -770,12 +769,11 @@ static bool HasPadding(const Type *Ty, const TargetData &TD,
}
} else if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
return HasPadding(ATy->getElementType(), TD, false);
return HasPadding(ATy->getElementType(), TD);
} else if (const VectorType *VTy = dyn_cast<VectorType>(Ty)) {
return HasPadding(VTy->getElementType(), TD, false);
return HasPadding(VTy->getElementType(), TD);
}
return inPacked ?
false : TD.getTypeSizeInBits(Ty) != TD.getABITypeSizeInBits(Ty);
return TD.getTypeSizeInBits(Ty) != TD.getABITypeSizeInBits(Ty);
}
/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of

14
test/Other/2008-06-04-FieldSizeInPacked.ll Normal file
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@ -0,0 +1,14 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep true
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
target triple = "x86_64-unknown-linux-gnu"
%packed = type <{ x86_fp80, i8 }>
%unpacked = type { x86_fp80, i8 }
define i1 @q() nounwind {
entry:
%char_p = getelementptr %packed* null, i32 0, i32 1 ; <i8*> [#uses=1]
%char_u = getelementptr %unpacked* null, i32 0, i32 1 ; <i8*> [#uses=1]
%res = icmp eq i8* %char_p, %char_u ; <i1> [#uses=1]
ret i1 %res
}