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Fold (and (setcc X, C1), (setcc X, C2))

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This is important for several reasons:

1. Benchmarks have lots of code that looks like this (perlbmk in particular):

  %tmp.2.i = setne int %tmp.0.i, 128              ; <bool> [#uses=1]
  %tmp.6343 = seteq int %tmp.0.i, 1               ; <bool> [#uses=1]
  %tmp.63 = and bool %tmp.2.i, %tmp.6343          ; <bool> [#uses=1]

   we now fold away the setne, a clear improvement.

2. In the more important cases, such as (X >= 10) & (X < 20), we now produce
   smaller code: (X-10) < 10.

3. Perhaps the nicest effect of this patch is that it really helps out the
   code generators.  In particular, for a 'range test' like the above,
   instead of generating this on X86 (the difference on PPC is even more
   pronounced):

        cmp %EAX, 50
        setge %CL
        cmp %EAX, 100
        setl %AL
        and %CL, %AL
        cmp %CL, 0

   we now generate this:

        add %EAX, -50
        cmp %EAX, 50

   Furthermore, this causes setcc's to be folded into branches more often.

These combinations trigger dozens of times in the spec benchmarks, particularly
in 176.gcc, 186.crafty, 253.perlbmk, 254.gap, & 099.go.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16559 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-09-28 21:48:02 +00:00
parent 7f12bbbc92
commit 955f331a77
1 changed files with 121 additions and 20 deletions
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141
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -137,7 +137,7 @@ namespace {
// InsertNewInstBefore - insert an instruction New before instruction Old
// in the program. Add the new instruction to the worklist.
//
Value *InsertNewInstBefore(Instruction *New, Instruction &Old) {
Instruction *InsertNewInstBefore(Instruction *New, Instruction &Old) {
assert(New && New->getParent() == 0 &&
"New instruction already inserted into a basic block!");
BasicBlock *BB = Old.getParent();
@ -334,6 +334,22 @@ static unsigned Log2(uint64_t Val) {
return Count;
}
// AddOne, SubOne - Add or subtract a constant one from an integer constant...
static Constant *AddOne(ConstantInt *C) {
return ConstantExpr::getAdd(C, ConstantInt::get(C->getType(), 1));
}
static Constant *SubOne(ConstantInt *C) {
return ConstantExpr::getSub(C, ConstantInt::get(C->getType(), 1));
}
// isTrueWhenEqual - Return true if the specified setcondinst instruction is
// true when both operands are equal...
//
static bool isTrueWhenEqual(Instruction &I) {
return I.getOpcode() == Instruction::SetEQ ||
I.getOpcode() == Instruction::SetGE ||
I.getOpcode() == Instruction::SetLE;
}
/// AssociativeOpt - Perform an optimization on an associative operator. This
/// function is designed to check a chain of associative operators for a
@ -1203,11 +1219,113 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
return BinaryOperator::createNot(Or);
}
// (setcc1 A, B) & (setcc2 A, B) --> (setcc3 A, B)
if (SetCondInst *RHS = dyn_cast<SetCondInst>(I.getOperand(1)))
if (SetCondInst *RHS = dyn_cast<SetCondInst>(Op1)) {
// (setcc1 A, B) & (setcc2 A, B) --> (setcc3 A, B)
if (Instruction *R = AssociativeOpt(I, FoldSetCCLogical(*this, RHS)))
return R;
Value *LHSVal, *RHSVal;
ConstantInt *LHSCst, *RHSCst;
Instruction::BinaryOps LHSCC, RHSCC;
if (match(Op0, m_SetCond(LHSCC, m_Value(LHSVal), m_ConstantInt(LHSCst))))
if (match(RHS, m_SetCond(RHSCC, m_Value(RHSVal), m_ConstantInt(RHSCst))))
if (LHSVal == RHSVal && // Found (X setcc C1) & (X setcc C2)
// Set[GL]E X, CST is folded to Set[GL]T elsewhere.
LHSCC != Instruction::SetGE && LHSCC != Instruction::SetLE &&
RHSCC != Instruction::SetGE && RHSCC != Instruction::SetLE) {
// Ensure that the larger constant is on the RHS.
Constant *Cmp = ConstantExpr::getSetGT(LHSCst, RHSCst);
SetCondInst *LHS = cast<SetCondInst>(Op0);
if (cast<ConstantBool>(Cmp)->getValue()) {
std::swap(LHS, RHS);
std::swap(LHSCst, RHSCst);
std::swap(LHSCC, RHSCC);
}
// At this point, we know we have have two setcc instructions
// comparing a value against two constants and and'ing the result
// together. Because of the above check, we know that we only have
// SetEQ, SetNE, SetLT, and SetGT here. We also know (from the
// FoldSetCCLogical check above), that the two constants are not
// equal.
assert(LHSCst != RHSCst && "Compares not folded above?");
switch (LHSCC) {
default: assert(0 && "Unknown integer condition code!");
case Instruction::SetEQ:
switch (RHSCC) {
default: assert(0 && "Unknown integer condition code!");
case Instruction::SetEQ: // (X == 13 & X == 15) -> false
case Instruction::SetGT: // (X == 13 & X > 15) -> false
return ReplaceInstUsesWith(I, ConstantBool::False);
case Instruction::SetNE: // (X == 13 & X != 15) -> X == 13
case Instruction::SetLT: // (X == 13 & X < 15) -> X == 13
return ReplaceInstUsesWith(I, LHS);
}
case Instruction::SetNE:
switch (RHSCC) {
default: assert(0 && "Unknown integer condition code!");
case Instruction::SetLT:
if (LHSCst == SubOne(RHSCst)) // (X != 13 & X < 14) -> X < 13
return new SetCondInst(Instruction::SetLT, LHSVal, LHSCst);
break; // (X != 13 & X < 15) -> no change
case Instruction::SetEQ: // (X != 13 & X == 15) -> X == 15
case Instruction::SetGT: // (X != 13 & X > 15) -> X > 15
return ReplaceInstUsesWith(I, RHS);
case Instruction::SetNE:
if (LHSCst == SubOne(RHSCst)) {// (X != 13 & X != 14) -> X-13 >u 1
Constant *AddCST = ConstantExpr::getNeg(LHSCst);
Instruction *Add = BinaryOperator::createAdd(LHSVal, AddCST,
LHSVal->getName()+".off");
InsertNewInstBefore(Add, I);
const Type *UnsType = Add->getType()->getUnsignedVersion();
Value *OffsetVal = InsertCastBefore(Add, UnsType, I);
AddCST = ConstantExpr::getSub(RHSCst, LHSCst);
AddCST = ConstantExpr::getCast(AddCST, UnsType);
return new SetCondInst(Instruction::SetGT, OffsetVal, AddCST);
}
break; // (X != 13 & X != 15) -> no change
}
break;
case Instruction::SetLT:
switch (RHSCC) {
default: assert(0 && "Unknown integer condition code!");
case Instruction::SetEQ: // (X < 13 & X == 15) -> false
case Instruction::SetGT: // (X < 13 & X > 15) -> false
return ReplaceInstUsesWith(I, ConstantBool::False);
case Instruction::SetNE: // (X < 13 & X != 15) -> X < 13
case Instruction::SetLT: // (X < 13 & X < 15) -> X < 13
return ReplaceInstUsesWith(I, LHS);
}
case Instruction::SetGT:
switch (RHSCC) {
default: assert(0 && "Unknown integer condition code!");
case Instruction::SetEQ: // (X > 13 & X == 15) -> X > 13
return ReplaceInstUsesWith(I, LHS);
case Instruction::SetGT: // (X > 13 & X > 15) -> X > 15
return ReplaceInstUsesWith(I, RHS);
case Instruction::SetNE:
if (RHSCst == AddOne(LHSCst)) // (X > 13 & X != 14) -> X > 14
return new SetCondInst(Instruction::SetGT, LHSVal, RHSCst);
break; // (X > 13 & X != 15) -> no change
case Instruction::SetLT: { // (X > 13 & X < 15) -> (X-14) <u 1
Constant *AddCST = ConstantExpr::getNeg(AddOne(LHSCst));
Instruction *Add = BinaryOperator::createAdd(LHSVal, AddCST,
LHSVal->getName()+".off");
InsertNewInstBefore(Add, I);
// Convert to unsigned for the comparison.
const Type *UnsType = Add->getType()->getUnsignedVersion();
Value *OffsetVal = InsertCastBefore(Add, UnsType, I);
AddCST = ConstantExpr::getAdd(AddCST, RHSCst);
AddCST = ConstantExpr::getCast(AddCST, UnsType);
return new SetCondInst(Instruction::SetLT, OffsetVal, AddCST);
}
break;
}
}
}
}
return Changed ? &I : 0;
}
@ -1429,23 +1547,6 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
return Changed ? &I : 0;
}
// AddOne, SubOne - Add or subtract a constant one from an integer constant...
static Constant *AddOne(ConstantInt *C) {
return ConstantExpr::getAdd(C, ConstantInt::get(C->getType(), 1));
}
static Constant *SubOne(ConstantInt *C) {
return ConstantExpr::getSub(C, ConstantInt::get(C->getType(), 1));
}
// isTrueWhenEqual - Return true if the specified setcondinst instruction is
// true when both operands are equal...
//
static bool isTrueWhenEqual(Instruction &I) {
return I.getOpcode() == Instruction::SetEQ ||
I.getOpcode() == Instruction::SetGE ||
I.getOpcode() == Instruction::SetLE;
}
Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
bool Changed = SimplifyCommutative(I);
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);