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Move some shift transforms out of instcombine and into InstructionSimplify.

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While there, I noticed that the transform "undef >>a X -> undef" was wrong.
For example if X is 2 then the top two bits must be equal, so the result can
not be anything.  I fixed this in the constant folder as well.  Also, I made
the transform for "X << undef" stronger: it now folds to undef always, even
though X might be zero.  This is in accordance with the LangRef, but I must
admit that it is fairly aggressive.  Also, I added "i32 X << 32 -> undef"
following the LangRef and the constant folder, likewise fairly aggressive.

llvm-svn: 123417
This commit is contained in:
Duncan Sands 2011-01-14 00:37:45 +00:00
parent e9841116c0
commit 44c273d907
5 changed files with 190 additions and 35 deletions
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25
include/llvm/Analysis/InstructionSimplify.h
View File

@ -35,16 +35,31 @@ namespace llvm {
Value *SimplifySubInst(Value *LHS, Value *RHS, bool isNSW, bool isNUW,
const TargetData *TD = 0, const DominatorTree *DT = 0);
/// SimplifyAndInst - Given operands for an And, see if we can
/// fold the result. If not, this returns null.
Value *SimplifyAndInst(Value *LHS, Value *RHS, const TargetData *TD = 0,
const DominatorTree *DT = 0);
/// SimplifyMulInst - Given operands for a Mul, see if we can
/// fold the result. If not, this returns null.
Value *SimplifyMulInst(Value *LHS, Value *RHS, const TargetData *TD = 0,
const DominatorTree *DT = 0);
/// SimplifyShlInst - Given operands for a Shl, see if we can
/// fold the result. If not, this returns null.
Value *SimplifyShlInst(Value *Op0, Value *Op1, const TargetData *TD = 0,
const DominatorTree *DT = 0);
/// SimplifyLShrInst - Given operands for a LShr, see if we can
/// fold the result. If not, this returns null.
Value *SimplifyLShrInst(Value *Op0, Value *Op1, const TargetData *TD = 0,
const DominatorTree *DT = 0);
/// SimplifyAShrInst - Given operands for a AShr, see if we can
/// fold the result. If not, this returns null.
Value *SimplifyAShrInst(Value *Op0, Value *Op1, const TargetData *TD = 0,
const DominatorTree *DT = 0);
/// SimplifyAndInst - Given operands for an And, see if we can
/// fold the result. If not, this returns null.
Value *SimplifyAndInst(Value *LHS, Value *RHS, const TargetData *TD = 0,
const DominatorTree *DT = 0);
/// SimplifyOrInst - Given operands for an Or, see if we can
/// fold the result. If not, this returns null.
Value *SimplifyOrInst(Value *LHS, Value *RHS, const TargetData *TD = 0,

142
lib/Analysis/InstructionSimplify.cpp
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@ -684,6 +684,136 @@ Value *llvm::SimplifyMulInst(Value *Op0, Value *Op1, const TargetData *TD,
return ::SimplifyMulInst(Op0, Op1, TD, DT, RecursionLimit);
}
/// SimplifyShlInst - Given operands for an Shl, see if we can
/// fold the result. If not, this returns null.
static Value *SimplifyShlInst(Value *Op0, Value *Op1, const TargetData *TD,
const DominatorTree *DT, unsigned MaxRecurse) {
if (Constant *C0 = dyn_cast<Constant>(Op0)) {
if (Constant *C1 = dyn_cast<Constant>(Op1)) {
Constant *Ops[] = { C0, C1 };
return ConstantFoldInstOperands(Instruction::Shl, C0->getType(), Ops, 2,
TD);
}
}
// 0 << X -> 0
if (match(Op0, m_Zero()))
return Op0;
// X << 0 -> X
if (match(Op1, m_Zero()))
return Op0;
// undef << X -> 0
if (isa<UndefValue>(Op0))
return Constant::getNullValue(Op0->getType());
// X << undef -> undef because it may shift by the bitwidth.
if (isa<UndefValue>(Op1))
return Op1;
// Shifting by the bitwidth or more is undefined.
if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1))
if (CI->getValue().getLimitedValue() >=
Op0->getType()->getScalarSizeInBits())
return UndefValue::get(Op0->getType());
return 0;
}
Value *llvm::SimplifyShlInst(Value *Op0, Value *Op1, const TargetData *TD,
const DominatorTree *DT) {
return ::SimplifyShlInst(Op0, Op1, TD, DT, RecursionLimit);
}
/// SimplifyLShrInst - Given operands for an LShr, see if we can
/// fold the result. If not, this returns null.
static Value *SimplifyLShrInst(Value *Op0, Value *Op1, const TargetData *TD,
const DominatorTree *DT, unsigned MaxRecurse) {
if (Constant *C0 = dyn_cast<Constant>(Op0)) {
if (Constant *C1 = dyn_cast<Constant>(Op1)) {
Constant *Ops[] = { C0, C1 };
return ConstantFoldInstOperands(Instruction::LShr, C0->getType(), Ops, 2,
TD);
}
}
// 0 >> X -> 0
if (match(Op0, m_Zero()))
return Op0;
// undef >>l X -> 0
if (isa<UndefValue>(Op0))
return Constant::getNullValue(Op0->getType());
// X >> 0 -> X
if (match(Op1, m_Zero()))
return Op0;
// X >> undef -> undef because it may shift by the bitwidth.
if (isa<UndefValue>(Op1))
return Op1;
// Shifting by the bitwidth or more is undefined.
if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1))
if (CI->getValue().getLimitedValue() >=
Op0->getType()->getScalarSizeInBits())
return UndefValue::get(Op0->getType());
return 0;
}
Value *llvm::SimplifyLShrInst(Value *Op0, Value *Op1, const TargetData *TD,
const DominatorTree *DT) {
return ::SimplifyLShrInst(Op0, Op1, TD, DT, RecursionLimit);
}
/// SimplifyAShrInst - Given operands for an AShr, see if we can
/// fold the result. If not, this returns null.
static Value *SimplifyAShrInst(Value *Op0, Value *Op1, const TargetData *TD,
const DominatorTree *DT, unsigned MaxRecurse) {
if (Constant *C0 = dyn_cast<Constant>(Op0)) {
if (Constant *C1 = dyn_cast<Constant>(Op1)) {
Constant *Ops[] = { C0, C1 };
return ConstantFoldInstOperands(Instruction::AShr, C0->getType(), Ops, 2,
TD);
}
}
// 0 >> X -> 0
if (match(Op0, m_Zero()))
return Op0;
// all ones >>a X -> all ones
if (match(Op0, m_AllOnes()))
return Op0;
// undef >>a X -> all ones
if (isa<UndefValue>(Op0))
return Constant::getAllOnesValue(Op0->getType());
// X >> 0 -> X
if (match(Op1, m_Zero()))
return Op0;
// X >> undef -> undef because it may shift by the bitwidth.
if (isa<UndefValue>(Op1))
return Op1;
// Shifting by the bitwidth or more is undefined.
if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1))
if (CI->getValue().getLimitedValue() >=
Op0->getType()->getScalarSizeInBits())
return UndefValue::get(Op0->getType());
return 0;
}
Value *llvm::SimplifyAShrInst(Value *Op0, Value *Op1, const TargetData *TD,
const DominatorTree *DT) {
return ::SimplifyAShrInst(Op0, Op1, TD, DT, RecursionLimit);
}
/// SimplifyAndInst - Given operands for an And, see if we can
/// fold the result. If not, this returns null.
static Value *SimplifyAndInst(Value *Op0, Value *Op1, const TargetData *TD,
@ -1267,6 +1397,9 @@ static Value *SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
/* isNUW */ false, TD, DT,
MaxRecurse);
case Instruction::Mul: return SimplifyMulInst(LHS, RHS, TD, DT, MaxRecurse);
case Instruction::Shl: return SimplifyShlInst(LHS, RHS, TD, DT, MaxRecurse);
case Instruction::LShr: return SimplifyLShrInst(LHS, RHS, TD, DT, MaxRecurse);
case Instruction::AShr: return SimplifyAShrInst(LHS, RHS, TD, DT, MaxRecurse);
case Instruction::And: return SimplifyAndInst(LHS, RHS, TD, DT, MaxRecurse);
case Instruction::Or: return SimplifyOrInst(LHS, RHS, TD, DT, MaxRecurse);
case Instruction::Xor: return SimplifyXorInst(LHS, RHS, TD, DT, MaxRecurse);
@ -1345,6 +1478,15 @@ Value *llvm::SimplifyInstruction(Instruction *I, const TargetData *TD,
case Instruction::Mul:
Result = SimplifyMulInst(I->getOperand(0), I->getOperand(1), TD, DT);
break;
case Instruction::Shl:
Result = SimplifyShlInst(I->getOperand(0), I->getOperand(1), TD, DT);
break;
case Instruction::LShr:
Result = SimplifyLShrInst(I->getOperand(0), I->getOperand(1), TD, DT);
break;
case Instruction::AShr:
Result = SimplifyAShrInst(I->getOperand(0), I->getOperand(1), TD, DT);
break;
case Instruction::And:
Result = SimplifyAndInst(I->getOperand(0), I->getOperand(1), TD, DT);
break;

36
lib/Transforms/InstCombine/InstCombineShifts.cpp
View File

@ -13,6 +13,7 @@
#include "InstCombine.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Support/PatternMatch.h"
using namespace llvm;
using namespace PatternMatch;
@ -21,25 +22,6 @@ Instruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) {
assert(I.getOperand(1)->getType() == I.getOperand(0)->getType());
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
// shl X, 0 == X and shr X, 0 == X
// shl 0, X == 0 and shr 0, X == 0
if (Op1 == Constant::getNullValue(Op1->getType()) ||
Op0 == Constant::getNullValue(Op0->getType()))
return ReplaceInstUsesWith(I, Op0);
if (isa<UndefValue>(Op0)) {
if (I.getOpcode() == Instruction::AShr) // undef >>s X -> undef
return ReplaceInstUsesWith(I, Op0);
else // undef << X -> 0, undef >>u X -> 0
return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
}
if (isa<UndefValue>(Op1)) {
if (I.getOpcode() == Instruction::AShr) // X >>s undef -> X
return ReplaceInstUsesWith(I, Op0);
else // X << undef, X >>u undef -> 0
return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
}
// See if we can fold away this shift.
if (SimplifyDemandedInstructionBits(I))
return &I;
@ -635,10 +617,15 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1,
}
Instruction *InstCombiner::visitShl(BinaryOperator &I) {
if (Value *V = SimplifyShlInst(I.getOperand(0), I.getOperand(1), TD))
return ReplaceInstUsesWith(I, V);
return commonShiftTransforms(I);
}
Instruction *InstCombiner::visitLShr(BinaryOperator &I) {
if (Value *V = SimplifyLShrInst(I.getOperand(0), I.getOperand(1), TD))
return ReplaceInstUsesWith(I, V);
if (Instruction *R = commonShiftTransforms(I))
return R;
@ -665,17 +652,14 @@ Instruction *InstCombiner::visitLShr(BinaryOperator &I) {
}
Instruction *InstCombiner::visitAShr(BinaryOperator &I) {
if (Value *V = SimplifyAShrInst(I.getOperand(0), I.getOperand(1), TD))
return ReplaceInstUsesWith(I, V);
if (Instruction *R = commonShiftTransforms(I))
return R;
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (ConstantInt *CSI = dyn_cast<ConstantInt>(Op0)) {
// ashr int -1, X = -1 (for any arithmetic shift rights of ~0)
if (CSI->isAllOnesValue())
return ReplaceInstUsesWith(I, CSI);
}
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
// If the input is a SHL by the same constant (ashr (shl X, C), C), then we
// have a sign-extend idiom.

4
lib/VMCore/ConstantFold.cpp
View File

@ -977,8 +977,8 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
return Constant::getNullValue(C1->getType()); // X lshr undef -> 0
// undef lshr X -> 0
case Instruction::AShr:
if (!isa<UndefValue>(C2))
return C1; // undef ashr X --> undef
if (!isa<UndefValue>(C2)) // undef ashr X --> all ones
return Constant::getAllOnesValue(C1->getType());
else if (isa<UndefValue>(C1))
return C1; // undef ashr undef -> undef
else

18
test/Transforms/InstCombine/shift.ll
View File

@ -35,18 +35,32 @@ define i32 @test4(i8 %A) {
define i32 @test5(i32 %A) {
; CHECK: @test5
; CHECK: ret i32 0
; CHECK: ret i32 undef
%B = lshr i32 %A, 32 ;; shift all bits out
ret i32 %B
}
define i32 @test5a(i32 %A) {
; CHECK: @test5a
; CHECK: ret i32 0
; CHECK: ret i32 undef
%B = shl i32 %A, 32 ;; shift all bits out
ret i32 %B
}
define i32 @test5b() {
; CHECK: @test5b
; CHECK: ret i32 -1
%B = ashr i32 undef, 2 ;; top two bits must be equal, so not undef
ret i32 %B
}
define i32 @test5b2(i32 %A) {
; CHECK: @test5b2
; CHECK: ret i32 -1
%B = ashr i32 undef, %A ;; top %A bits must be equal, so not undef
ret i32 %B
}
define i32 @test6(i32 %A) {
; CHECK: @test6
; CHECK-NEXT: mul i32 %A, 6