According to my auto-simplifier the most common missed simplifications in

optimized code are:
  (non-negative number)+(power-of-two) != 0 -> true
and
  (x | 1) != 0 -> true
Instcombine knows about the second one of course, but only does it if X|1
has only one use.  These fire thousands of times in the testsuite.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124183 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2011-01-25 09:38:29 +00:00
parent b38824f866
commit d70d1a5c44
4 changed files with 299 additions and 13 deletions

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@ -39,6 +39,23 @@ namespace llvm {
APInt &KnownOne, const TargetData *TD = 0, APInt &KnownOne, const TargetData *TD = 0,
unsigned Depth = 0); unsigned Depth = 0);
/// ComputeSignBit - Determine whether the sign bit is known to be zero or
/// one. Convenience wrapper around ComputeMaskedBits.
void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
const TargetData *TD = 0, unsigned Depth = 0);
/// isPowerOfTwo - Return true if the given value is known to have exactly one
/// bit set when defined. For vectors return true if every element is known to
/// be a power of two when defined. Supports values with integer or pointer
/// type and vectors of integers.
bool isPowerOfTwo(Value *V, const TargetData *TD = 0, unsigned Depth = 0);
/// isKnownNonZero - Return true if the given value is known to be non-zero
/// when defined. For vectors return true if every element is known to be
/// non-zero when defined. Supports values with integer or pointer type and
/// vectors of integers.
bool isKnownNonZero(Value *V, const TargetData *TD = 0, unsigned Depth = 0);
/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
/// this predicate to simplify operations downstream. Mask is known to be /// this predicate to simplify operations downstream. Mask is known to be
/// zero for bits that V cannot have. /// zero for bits that V cannot have.

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@ -22,6 +22,7 @@
#include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ConstantFolding.h" #include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/Dominators.h" #include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Support/PatternMatch.h" #include "llvm/Support/PatternMatch.h"
#include "llvm/Support/ValueHandle.h" #include "llvm/Support/ValueHandle.h"
#include "llvm/Target/TargetData.h" #include "llvm/Target/TargetData.h"
@ -1153,7 +1154,69 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
} }
} }
// See if we are doing a comparison with a constant. // icmp <alloca*>, <global/alloca*/null> - Different stack variables have
// different addresses, and what's more the address of a stack variable is
// never null or equal to the address of a global. Note that generalizing
// to the case where LHS is a global variable address or null is pointless,
// since if both LHS and RHS are constants then we already constant folded
// the compare, and if only one of them is then we moved it to RHS already.
if (isa<AllocaInst>(LHS) && (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
isa<ConstantPointerNull>(RHS)))
// We already know that LHS != LHS.
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
// If we are comparing with zero then try hard since this is a common case.
if (match(RHS, m_Zero())) {
bool LHSKnownNonNegative, LHSKnownNegative;
switch (Pred) {
default:
assert(false && "Unknown ICmp predicate!");
case ICmpInst::ICMP_ULT:
return ConstantInt::getFalse(LHS->getContext());
case ICmpInst::ICMP_UGE:
return ConstantInt::getTrue(LHS->getContext());
case ICmpInst::ICMP_EQ:
case ICmpInst::ICMP_ULE:
if (isKnownNonZero(LHS, TD))
return ConstantInt::getFalse(LHS->getContext());
break;
case ICmpInst::ICMP_NE:
case ICmpInst::ICMP_UGT:
if (isKnownNonZero(LHS, TD))
return ConstantInt::getTrue(LHS->getContext());
break;
case ICmpInst::ICMP_SLT:
ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, TD);
if (LHSKnownNegative)
return ConstantInt::getTrue(LHS->getContext());
if (LHSKnownNonNegative)
return ConstantInt::getFalse(LHS->getContext());
break;
case ICmpInst::ICMP_SLE:
ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, TD);
if (LHSKnownNegative)
return ConstantInt::getTrue(LHS->getContext());
if (LHSKnownNonNegative && isKnownNonZero(LHS, TD))
return ConstantInt::getFalse(LHS->getContext());
break;
case ICmpInst::ICMP_SGE:
ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, TD);
if (LHSKnownNegative)
return ConstantInt::getFalse(LHS->getContext());
if (LHSKnownNonNegative)
return ConstantInt::getTrue(LHS->getContext());
break;
case ICmpInst::ICMP_SGT:
ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, TD);
if (LHSKnownNegative)
return ConstantInt::getFalse(LHS->getContext());
if (LHSKnownNonNegative && isKnownNonZero(LHS, TD))
return ConstantInt::getTrue(LHS->getContext());
break;
}
}
// See if we are doing a comparison with a constant integer.
if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) { if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
switch (Pred) { switch (Pred) {
default: break; default: break;
@ -1192,17 +1255,6 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
} }
} }
// icmp <alloca*>, <global/alloca*/null> - Different stack variables have
// different addresses, and what's more the address of a stack variable is
// never null or equal to the address of a global. Note that generalizing
// to the case where LHS is a global variable address or null is pointless,
// since if both LHS and RHS are constants then we already constant folded
// the compare, and if only one of them is then we moved it to RHS already.
if (isa<AllocaInst>(LHS) && (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
isa<ConstantPointerNull>(RHS)))
// We already know that LHS != LHS.
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
// Compare of cast, for example (zext X) != 0 -> X != 0 // Compare of cast, for example (zext X) != 0 -> X != 0
if (isa<CastInst>(LHS) && (isa<Constant>(RHS) || isa<CastInst>(RHS))) { if (isa<CastInst>(LHS) && (isa<Constant>(RHS) || isa<CastInst>(RHS))) {
Instruction *LI = cast<CastInst>(LHS); Instruction *LI = cast<CastInst>(LHS);

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@ -24,9 +24,22 @@
#include "llvm/Target/TargetData.h" #include "llvm/Target/TargetData.h"
#include "llvm/Support/GetElementPtrTypeIterator.h" #include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/MathExtras.h" #include "llvm/Support/MathExtras.h"
#include "llvm/Support/PatternMatch.h"
#include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallPtrSet.h"
#include <cstring> #include <cstring>
using namespace llvm; using namespace llvm;
using namespace llvm::PatternMatch;
const unsigned MaxDepth = 6;
/// getBitWidth - Returns the bitwidth of the given scalar or pointer type (if
/// unknown returns 0). For vector types, returns the element type's bitwidth.
static unsigned getBitWidth(const Type *Ty, const TargetData *TD) {
if (unsigned BitWidth = Ty->getScalarSizeInBits())
return BitWidth;
assert(isa<PointerType>(Ty) && "Expected a pointer type!");
return TD ? TD->getPointerSizeInBits() : 0;
}
/// ComputeMaskedBits - Determine which of the bits specified in Mask are /// ComputeMaskedBits - Determine which of the bits specified in Mask are
/// known to be either zero or one and return them in the KnownZero/KnownOne /// known to be either zero or one and return them in the KnownZero/KnownOne
@ -47,7 +60,6 @@ using namespace llvm;
void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
APInt &KnownZero, APInt &KnownOne, APInt &KnownZero, APInt &KnownOne,
const TargetData *TD, unsigned Depth) { const TargetData *TD, unsigned Depth) {
const unsigned MaxDepth = 6;
assert(V && "No Value?"); assert(V && "No Value?");
assert(Depth <= MaxDepth && "Limit Search Depth"); assert(Depth <= MaxDepth && "Limit Search Depth");
unsigned BitWidth = Mask.getBitWidth(); unsigned BitWidth = Mask.getBitWidth();
@ -620,6 +632,157 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
} }
} }
/// ComputeSignBit - Determine whether the sign bit is known to be zero or
/// one. Convenience wrapper around ComputeMaskedBits.
void llvm::ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
const TargetData *TD, unsigned Depth) {
unsigned BitWidth = getBitWidth(V->getType(), TD);
if (!BitWidth) {
KnownZero = false;
KnownOne = false;
return;
}
APInt ZeroBits(BitWidth, 0);
APInt OneBits(BitWidth, 0);
ComputeMaskedBits(V, APInt::getSignBit(BitWidth), ZeroBits, OneBits, TD,
Depth);
KnownOne = OneBits[BitWidth - 1];
KnownZero = ZeroBits[BitWidth - 1];
}
/// isPowerOfTwo - Return true if the given value is known to have exactly one
/// bit set when defined. For vectors return true if every element is known to
/// be a power of two when defined. Supports values with integer or pointer
/// types and vectors of integers.
bool llvm::isPowerOfTwo(Value *V, const TargetData *TD, unsigned Depth) {
if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
return CI->getValue().countPopulation() == 1;
// TODO: Handle vector constants.
// 1 << X is clearly a power of two if the one is not shifted off the end. If
// it is shifted off the end then the result is undefined.
if (match(V, m_Shl(m_One(), m_Value())))
return true;
// (signbit) >>l X is clearly a power of two if the one is not shifted off the
// bottom. If it is shifted off the bottom then the result is undefined.
ConstantInt *CI;
if (match(V, m_LShr(m_ConstantInt(CI), m_Value())) &&
CI->getValue().isSignBit())
return true;
// The remaining tests are all recursive, so bail out if we hit the limit.
if (Depth++ == MaxDepth)
return false;
if (ZExtInst *ZI = dyn_cast<ZExtInst>(V))
return isPowerOfTwo(ZI->getOperand(0), TD, Depth);
if (SelectInst *SI = dyn_cast<SelectInst>(V))
return isPowerOfTwo(SI->getTrueValue(), TD, Depth) &&
isPowerOfTwo(SI->getFalseValue(), TD, Depth);
return false;
}
/// isKnownNonZero - Return true if the given value is known to be non-zero
/// when defined. For vectors return true if every element is known to be
/// non-zero when defined. Supports values with integer or pointer type and
/// vectors of integers.
bool llvm::isKnownNonZero(Value *V, const TargetData *TD, unsigned Depth) {
if (Constant *C = dyn_cast<Constant>(V)) {
if (C->isNullValue())
return false;
if (isa<ConstantInt>(C))
// Must be non-zero due to null test above.
return true;
// TODO: Handle vectors
return false;
}
// The remaining tests are all recursive, so bail out if we hit the limit.
if (Depth++ == MaxDepth)
return false;
unsigned BitWidth = getBitWidth(V->getType(), TD);
// X | Y != 0 if X != 0 or Y != 0.
Value *X = 0, *Y = 0;
if (match(V, m_Or(m_Value(X), m_Value(Y))))
return isKnownNonZero(X, TD, Depth) || isKnownNonZero(Y, TD, Depth);
// ext X != 0 if X != 0.
if (isa<SExtInst>(V) || isa<ZExtInst>(V))
return isKnownNonZero(cast<Instruction>(V)->getOperand(0), TD, Depth);
// shl X, A != 0 if X is odd. Note that the value of the shift is undefined
// if the lowest bit is shifted off the end.
if (BitWidth && match(V, m_Shl(m_Value(X), m_Value(Y)))) {
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
ComputeMaskedBits(V, APInt(BitWidth, 1), KnownZero, KnownOne, TD, Depth);
if (KnownOne[0])
return true;
}
// shr X, A != 0 if X is negative. Note that the value of the shift is not
// defined if the sign bit is shifted off the end.
else if (match(V, m_Shr(m_Value(X), m_Value(Y)))) {
bool XKnownNonNegative, XKnownNegative;
ComputeSignBit(X, XKnownNonNegative, XKnownNegative, TD, Depth);
if (XKnownNegative)
return true;
}
// X + Y.
else if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
bool XKnownNonNegative, XKnownNegative;
bool YKnownNonNegative, YKnownNegative;
ComputeSignBit(X, XKnownNonNegative, XKnownNegative, TD, Depth);
ComputeSignBit(Y, YKnownNonNegative, YKnownNegative, TD, Depth);
// If X and Y are both non-negative (as signed values) then their sum is not
// zero.
if (XKnownNonNegative && YKnownNonNegative)
return true;
// If X and Y are both negative (as signed values) then their sum is not
// zero unless both X and Y equal INT_MIN.
if (BitWidth && XKnownNegative && YKnownNegative) {
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
APInt Mask = APInt::getSignedMaxValue(BitWidth);
// The sign bit of X is set. If some other bit is set then X is not equal
// to INT_MIN.
ComputeMaskedBits(X, Mask, KnownZero, KnownOne, TD, Depth);
if ((KnownOne & Mask) != 0)
return true;
// The sign bit of Y is set. If some other bit is set then Y is not equal
// to INT_MIN.
ComputeMaskedBits(Y, Mask, KnownZero, KnownOne, TD, Depth);
if ((KnownOne & Mask) != 0)
return true;
}
// The sum of a non-negative number and a power of two is not zero.
if (XKnownNonNegative && isPowerOfTwo(Y, TD, Depth))
return true;
if (YKnownNonNegative && isPowerOfTwo(X, TD, Depth))
return true;
}
// (C ? X : Y) != 0 if X != 0 and Y != 0.
else if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
if (isKnownNonZero(SI->getTrueValue(), TD, Depth) &&
isKnownNonZero(SI->getFalseValue(), TD, Depth))
return true;
}
if (!BitWidth) return false;
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
ComputeMaskedBits(V, APInt::getAllOnesValue(BitWidth), KnownZero, KnownOne,
TD, Depth);
return KnownOne != 0;
}
/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
/// this predicate to simplify operations downstream. Mask is known to be zero /// this predicate to simplify operations downstream. Mask is known to be zero
/// for bits that V cannot have. /// for bits that V cannot have.

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@ -27,6 +27,14 @@ define i1 @zext2(i1 %x) {
; CHECK: ret i1 %x ; CHECK: ret i1 %x
} }
define i1 @zext3() {
; CHECK: @zext3
%e = zext i1 1 to i32
%c = icmp ne i32 %e, 0
ret i1 %c
; CHECK: ret i1 true
}
define i1 @sext(i32 %x) { define i1 @sext(i32 %x) {
; CHECK: @sext ; CHECK: @sext
%e1 = sext i32 %x to i64 %e1 = sext i32 %x to i64
@ -43,3 +51,49 @@ define i1 @sext2(i1 %x) {
ret i1 %c ret i1 %c
; CHECK: ret i1 %x ; CHECK: ret i1 %x
} }
define i1 @sext3() {
; CHECK: @sext3
%e = sext i1 1 to i32
%c = icmp ne i32 %e, 0
ret i1 %c
; CHECK: ret i1 true
}
define i1 @add(i32 %x, i32 %y) {
; CHECK: @add
%l = lshr i32 %x, 1
%r = lshr i32 %y, 1
%s = add i32 %l, %r
%c = icmp eq i32 %s, 0
ret i1 %c
; CHECK: ret i1 false
}
define i1 @add2(i8 %x, i8 %y) {
; CHECK: @add2
%l = or i8 %x, 128
%r = or i8 %y, 129
%s = add i8 %l, %r
%c = icmp eq i8 %s, 0
ret i1 %c
; CHECK: ret i1 false
}
define i1 @addpowtwo(i32 %x, i32 %y) {
; CHECK: @addpowtwo
%l = lshr i32 %x, 1
%r = shl i32 1, %y
%s = add i32 %l, %r
%c = icmp eq i32 %s, 0
ret i1 %c
; CHECK: ret i1 false
}
define i1 @or(i32 %x) {
; CHECK: @or
%o = or i32 %x, 1
%c = icmp eq i32 %o, 0
ret i1 %c
; CHECK: ret i1 false
}