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Generalize the new code in instcombine's ComputeNumSignBits for handling

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and/or to handle more cases (such as this add-sitofp.ll testcase), and
port it to selectiondag's ComputeNumSignBits.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51469 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2008-05-23 02:28:01 +00:00
parent e4977cf750
commit a332f17c8c
3 changed files with 31 additions and 51 deletions
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20
lib/CodeGen/SelectionDAG/SelectionDAG.cpp
View File

@ -1628,6 +1628,7 @@ unsigned SelectionDAG::ComputeNumSignBits(SDOperand Op, unsigned Depth) const{
assert(MVT::isInteger(VT) && "Invalid VT!");
unsigned VTBits = MVT::getSizeInBits(VT);
unsigned Tmp, Tmp2;
unsigned FirstAnswer = 1;
if (Depth == 6)
return 1; // Limit search depth.
@ -1683,11 +1684,16 @@ unsigned SelectionDAG::ComputeNumSignBits(SDOperand Op, unsigned Depth) const{
case ISD::AND:
case ISD::OR:
case ISD::XOR: // NOT is handled here.
// Logical binary ops preserve the number of sign bits.
// Logical binary ops preserve the number of sign bits at the worst.
Tmp = ComputeNumSignBits(Op.getOperand(0), Depth+1);
if (Tmp == 1) return 1; // Early out.
Tmp2 = ComputeNumSignBits(Op.getOperand(1), Depth+1);
return std::min(Tmp, Tmp2);
if (Tmp != 1) {
Tmp2 = ComputeNumSignBits(Op.getOperand(1), Depth+1);
FirstAnswer = std::min(Tmp, Tmp2);
// We computed what we know about the sign bits as our first
// answer. Now proceed to the generic code that uses
// ComputeMaskedBits, and pick whichever answer is better.
}
break;
case ISD::SELECT:
Tmp = ComputeNumSignBits(Op.getOperand(1), Depth+1);
@ -1801,7 +1807,7 @@ unsigned SelectionDAG::ComputeNumSignBits(SDOperand Op, unsigned Depth) const{
Op.getOpcode() == ISD::INTRINSIC_W_CHAIN ||
Op.getOpcode() == ISD::INTRINSIC_VOID) {
unsigned NumBits = TLI.ComputeNumSignBitsForTargetNode(Op, Depth);
if (NumBits > 1) return NumBits;
if (NumBits > 1) FirstAnswer = std::max(FirstAnswer, NumBits);
}
// Finally, if we can prove that the top bits of the result are 0's or 1's,
@ -1816,7 +1822,7 @@ unsigned SelectionDAG::ComputeNumSignBits(SDOperand Op, unsigned Depth) const{
Mask = KnownOne;
} else {
// Nothing known.
return 1;
return FirstAnswer;
}
// Okay, we know that the sign bit in Mask is set. Use CLZ to determine
@ -1825,7 +1831,7 @@ unsigned SelectionDAG::ComputeNumSignBits(SDOperand Op, unsigned Depth) const{
Mask <<= Mask.getBitWidth()-VTBits;
// Return # leading zeros. We use 'min' here in case Val was zero before
// shifting. We don't want to return '64' as for an i32 "0".
return std::min(VTBits, Mask.countLeadingZeros());
return std::max(FirstAnswer, std::min(VTBits, Mask.countLeadingZeros()));
}

53
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -2072,6 +2072,7 @@ unsigned InstCombiner::ComputeNumSignBits(Value *V, unsigned Depth) const{
const IntegerType *Ty = cast<IntegerType>(V->getType());
unsigned TyBits = Ty->getBitWidth();
unsigned Tmp, Tmp2;
unsigned FirstAnswer = 1;
if (Depth == 6)
return 1; // Limit search depth.
@ -2101,54 +2102,18 @@ unsigned InstCombiner::ComputeNumSignBits(Value *V, unsigned Depth) const{
}
break;
case Instruction::And:
// Logical binary ops preserve the number of sign bits at the worst.
Tmp = ComputeNumSignBits(U->getOperand(0), Depth+1);
if (Tmp != 1) {
Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth+1);
Tmp = std::min(Tmp, Tmp2);
}
// X & C has sign bits equal to C if C's top bits are zeros.
if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) {
// See what bits are known to be zero on the output.
APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
APInt Mask = APInt::getAllOnesValue(TyBits);
ComputeMaskedBits(U->getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
KnownZero |= ~C->getValue();
// If we know that we have leading zeros, we know we have at least that
// many sign bits.
Tmp = std::max(Tmp, KnownZero.countLeadingOnes());
}
return Tmp;
case Instruction::Or:
case Instruction::Xor: // NOT is handled here.
// Logical binary ops preserve the number of sign bits at the worst.
Tmp = ComputeNumSignBits(U->getOperand(0), Depth+1);
if (Tmp != 1) {
Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth+1);
Tmp = std::min(Tmp, Tmp2);
FirstAnswer = std::min(Tmp, Tmp2);
// We computed what we know about the sign bits as our first
// answer. Now proceed to the generic code that uses
// ComputeMaskedBits, and pick whichever answer is better.
}
// X & C has sign bits equal to C if C's top bits are zeros.
if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) {
// See what bits are known to be one on the output.
APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
APInt Mask = APInt::getAllOnesValue(TyBits);
ComputeMaskedBits(U->getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
KnownOne |= C->getValue();
// If we know that we have leading ones, we know we have at least that
// many sign bits.
Tmp = std::max(Tmp, KnownOne.countLeadingOnes());
}
return Tmp;
case Instruction::Xor: // NOT is handled here.
// Logical binary ops preserve the number of sign bits.
Tmp = ComputeNumSignBits(U->getOperand(0), Depth+1);
if (Tmp == 1) return 1; // Early out.
Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth+1);
return std::min(Tmp, Tmp2);
break;
case Instruction::Select:
Tmp = ComputeNumSignBits(U->getOperand(1), Depth+1);
@ -2232,7 +2197,7 @@ unsigned InstCombiner::ComputeNumSignBits(Value *V, unsigned Depth) const{
Mask = KnownOne;
} else {
// Nothing known.
return 1;
return FirstAnswer;
}
// Okay, we know that the sign bit in Mask is set. Use CLZ to determine
@ -2241,7 +2206,7 @@ unsigned InstCombiner::ComputeNumSignBits(Value *V, unsigned Depth) const{
Mask <<= Mask.getBitWidth()-TyBits;
// Return # leading zeros. We use 'min' here in case Val was zero before
// shifting. We don't want to return '64' as for an i32 "0".
return std::min(TyBits, Mask.countLeadingZeros());
return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros()));
}

9
test/Transforms/InstCombine/add-sitofp.ll Normal file
View File

@ -0,0 +1,9 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {add i32}
define double @x(i32 %a, i32 %b) nounwind {
%m = lshr i32 %a, 24
%n = and i32 %m, %b
%o = sitofp i32 %n to double
%p = add double %o, 1.0
ret double %p
}