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Teach vm core to more aggressively fold 'trunc' constantexprs,

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allowing it to simplify the crazy constantexprs in the testcases
down to something sensible.  This allows -std-compile-opts to
completely "devirtualize" the pointers to member functions in
the testcase from PR5176.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84368 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2009-10-17 21:53:27 +00:00
parent 5e5c4d3d5a
commit 59c4eba416
2 changed files with 178 additions and 9 deletions
lib/VMCore
ConstantFold.cpp
test/Transforms/ConstProp
constant-expr.ll

169
lib/VMCore/ConstantFold.cpp

@ -179,6 +179,151 @@ static Constant *FoldBitCast(LLVMContext &Context,
}
/// ExtractConstantBytes - V is an integer constant which only has a subset of
/// its bytes used. The bytes used are indicated by ByteStart (which is the
/// first byte used, counting from the least significant byte) and ByteSize,
/// which is the number of bytes used.
///
/// This function analyzes the specified constant to see if the specified byte
/// range can be returned as a simplified constant. If so, the constant is
/// returned, otherwise null is returned.
///
static Constant *ExtractConstantBytes(Constant *C, unsigned ByteStart,
unsigned ByteSize) {
assert(isa<IntegerType>(C->getType()) &&
(cast<IntegerType>(C->getType())->getBitWidth() & 7) == 0 &&
"Non-byte sized integer input");
unsigned CSize = cast<IntegerType>(C->getType())->getBitWidth()/8;
assert(ByteSize && "Must be accessing some piece");
assert(ByteStart+ByteSize <= CSize && "Extracting invalid piece from input");
assert(ByteSize != CSize && "Should not extract everything");
// Constant Integers are simple.
if (ConstantInt *CI = dyn_cast<ConstantInt>(C)) {
APInt V = CI->getValue();
if (ByteStart)
V = V.lshr(ByteStart*8);
V.trunc(ByteSize*8);
return ConstantInt::get(CI->getContext(), V);
}
// In the input is a constant expr, we might be able to recursively simplify.
// If not, we definitely can't do anything.
ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
if (CE == 0) return 0;
switch (CE->getOpcode()) {
default: return 0;
case Instruction::Or: {
Constant *RHS = ExtractConstantBytes(C->getOperand(1), ByteStart, ByteSize);
if (RHS == 0)
return 0;
// X | -1 -> -1.
if (ConstantInt *RHSC = dyn_cast<ConstantInt>(RHS))
if (RHSC->isAllOnesValue())
return RHSC;
Constant *LHS = ExtractConstantBytes(C->getOperand(0), ByteStart, ByteSize);
if (LHS == 0)
return 0;
return ConstantExpr::getOr(LHS, RHS);
}
case Instruction::And: {
Constant *RHS = ExtractConstantBytes(C->getOperand(1), ByteStart, ByteSize);
if (RHS == 0)
return 0;
// X & 0 -> 0.
if (RHS->isNullValue())
return RHS;
Constant *LHS = ExtractConstantBytes(C->getOperand(0), ByteStart, ByteSize);
if (LHS == 0)
return 0;
return ConstantExpr::getAnd(LHS, RHS);
}
case Instruction::LShr: {
ConstantInt *Amt = dyn_cast<ConstantInt>(CE->getOperand(1));
if (Amt == 0)
return 0;
unsigned ShAmt = Amt->getZExtValue();
// Cannot analyze non-byte shifts.
if ((ShAmt & 7) != 0)
return 0;
ShAmt >>= 3;
// If the extract is known to be all zeros, return zero.
if (ByteStart >= CSize-ShAmt)
return Constant::getNullValue(IntegerType::get(CE->getContext(),
ByteSize*8));
// If the extract is known to be fully in the input, extract it.
if (ByteStart+ByteSize+ShAmt <= CSize)
return ExtractConstantBytes(C->getOperand(0), ByteStart+ShAmt, ByteSize);
// TODO: Handle the 'partially zero' case.
return 0;
}
case Instruction::Shl: {
ConstantInt *Amt = dyn_cast<ConstantInt>(CE->getOperand(1));
if (Amt == 0)
return 0;
unsigned ShAmt = Amt->getZExtValue();
// Cannot analyze non-byte shifts.
if ((ShAmt & 7) != 0)
return 0;
ShAmt >>= 3;
// If the extract is known to be all zeros, return zero.
if (ByteStart+ByteSize <= ShAmt)
return Constant::getNullValue(IntegerType::get(CE->getContext(),
ByteSize*8));
// If the extract is known to be fully in the input, extract it.
if (ByteStart >= ShAmt)
return ExtractConstantBytes(C->getOperand(0), ByteStart-ShAmt, ByteSize);
// TODO: Handle the 'partially zero' case.
return 0;
}
case Instruction::ZExt: {
unsigned SrcBitSize =
cast<IntegerType>(C->getOperand(0)->getType())->getBitWidth();
// If extracting something that is completely zero, return 0.
if (ByteStart*8 >= SrcBitSize)
return Constant::getNullValue(IntegerType::get(CE->getContext(),
ByteSize*8));
// If exactly extracting the input, return it.
if (ByteStart == 0 && ByteSize*8 == SrcBitSize)
return C->getOperand(0);
// If extracting something completely in the input, if if the input is a
// multiple of 8 bits, recurse.
if ((SrcBitSize&7) == 0 && (ByteStart+ByteSize)*8 <= SrcBitSize)
return ExtractConstantBytes(C->getOperand(0), ByteStart, ByteSize);
// Otherwise, if extracting a subset of the input, which is not multiple of
// 8 bits, do a shift and trunc to get the bits.
if ((ByteStart+ByteSize)*8 < SrcBitSize) {
assert((SrcBitSize&7) && "Shouldn't get byte sized case here");
Constant *Res = C->getOperand(0);
if (ByteStart)
Res = ConstantExpr::getLShr(Res,
ConstantInt::get(Res->getType(), ByteStart*8));
return ConstantExpr::getTrunc(Res, IntegerType::get(C->getContext(),
ByteSize*8));
}
// TODO: Handle the 'partially zero' case.
return 0;
}
}
}
Constant *llvm::ConstantFoldCastInstruction(LLVMContext &Context,
unsigned opc, Constant *V,
const Type *DestTy) {
@ -236,6 +381,8 @@ Constant *llvm::ConstantFoldCastInstruction(LLVMContext &Context,
// We actually have to do a cast now. Perform the cast according to the
// opcode specified.
switch (opc) {
default:
llvm_unreachable("Failed to cast constant expression");
case Instruction::FPTrunc:
case Instruction::FPExt:
if (ConstantFP *FPC = dyn_cast<ConstantFP>(V)) {
@ -300,23 +447,27 @@ Constant *llvm::ConstantFoldCastInstruction(LLVMContext &Context,
return ConstantInt::get(Context, Result);
}
return 0;
case Instruction::Trunc:
case Instruction::Trunc: {
uint32_t DestBitWidth = cast<IntegerType>(DestTy)->getBitWidth();
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
uint32_t BitWidth = cast<IntegerType>(DestTy)->getBitWidth();
APInt Result(CI->getValue());
Result.trunc(BitWidth);
Result.trunc(DestBitWidth);
return ConstantInt::get(Context, Result);
}
// The input must be a constantexpr. See if we can simplify this based on
// the bytes we are demanding. Only do this if the source and dest are an
// even multiple of a byte.
if ((DestBitWidth & 7) == 0 &&
(cast<IntegerType>(V->getType())->getBitWidth() & 7) == 0)
if (Constant *Res = ExtractConstantBytes(V, 0, DestBitWidth / 8))
return Res;
return 0;
}
case Instruction::BitCast:
return FoldBitCast(Context, V, DestTy);
default:
assert(!"Invalid CE CastInst opcode");
break;
}
llvm_unreachable("Failed to cast constant expression");
return 0;
}
Constant *llvm::ConstantFoldSelectInstruction(LLVMContext&,

18
test/Transforms/ConstProp/constant-expr.ll

@ -40,3 +40,21 @@
@O = global i1 icmp eq (i32 zext (i1 icmp ult (i8* @X, i8* @Y) to i32), i32 0)
; CHECK: @O = global i1 icmp uge (i8* @X, i8* @Y)
; PR5176
; CHECK: @T1 = global i1 true
@T1 = global i1 icmp eq (i64 and (i64 trunc (i256 lshr (i256 or (i256 and (i256 and (i256 shl (i256 zext (i64 ptrtoint (i1* @B to i64) to i256), i256 64), i256 -6277101735386680763495507056286727952638980837032266301441), i256 6277101735386680763835789423207666416102355444464034512895), i256 shl (i256 zext (i64 ptrtoint (i1* @A to i64) to i256), i256 192)), i256 64) to i64), i64 1), i64 0)
; CHECK: @T2 = global i1* @B
@T2 = global i1* inttoptr (i64 add (i64 trunc (i256 lshr (i256 or (i256 and (i256 and (i256 shl (i256 zext (i64 ptrtoint (i1* @A to i64) to i256), i256 64), i256 -6277101735386680763495507056286727952638980837032266301441), i256 6277101735386680763835789423207666416102355444464034512895), i256 shl (i256 zext (i64 ptrtoint (i1* @B to i64) to i256), i256 192)), i256 192) to i64), i64 trunc (i256 lshr (i256 or (i256 and (i256 and (i256 shl (i256 zext (i64 ptrtoint (i1* @A to i64) to i256), i256 64), i256 -6277101735386680763495507056286727952638980837032266301441), i256 6277101735386680763835789423207666416102355444464034512895), i256 shl (i256 zext (i64 ptrtoint (i1* @B to i64) to i256), i256 192)), i256 128) to i64)) to i1*)
; CHECK: @T3 = global i64 add (i64 ptrtoint (i1* @B to i64), i64 -1)
@T3 = global i64 add (i64 trunc (i256 lshr (i256 or (i256 and (i256 and (i256 shl (i256 zext (i64 ptrtoint (i1* @B to i64) to i256), i256 64), i256 -6277101735386680763495507056286727952638980837032266301441), i256 6277101735386680763835789423207666416102355444464034512895), i256 shl (i256 zext (i64 ptrtoint (i1* @A to i64) to i256), i256 192)), i256 64) to i64), i64 -1)
; CHECK: @T4 = global i1* @B
@T4 = global i1* inttoptr (i64 trunc (i256 lshr (i256 or (i256 and (i256 and (i256 shl (i256 zext (i64 ptrtoint (i1* @B to i64) to i256), i256 64), i256 -6277101735386680763495507056286727952638980837032266301441), i256 6277101735386680763835789423207666416102355444464034512895), i256 shl (i256 zext (i64 ptrtoint (i1* @A to i64) to i256), i256 192)), i256 64) to i64) to i1*)
; CHECK: @T5 = global i1* @A
@T5 = global i1* inttoptr (i64 add (i64 trunc (i256 lshr (i256 or (i256 and (i256 and (i256 shl (i256 zext (i64 ptrtoint (i1* @B to i64) to i256), i256 64), i256 -6277101735386680763495507056286727952638980837032266301441), i256 6277101735386680763835789423207666416102355444464034512895), i256 shl (i256 zext (i64 ptrtoint (i1* @A to i64) to i256), i256 192)), i256 192) to i64), i64 trunc (i256 lshr (i256 or (i256 and (i256 and (i256 shl (i256 zext (i64 ptrtoint (i1* @B to i64) to i256), i256 64), i256 -6277101735386680763495507056286727952638980837032266301441), i256 6277101735386680763835789423207666416102355444464034512895), i256 shl (i256 zext (i64 ptrtoint (i1* @A to i64) to i256), i256 192)), i256 128) to i64)) to i1*)