Generalize the new code in instcombine's ComputeNumSignBits for handling
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
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 084f874..13dbc11 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -2072,6 +2072,7 @@
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 @@
}
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 @@
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 @@
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()));
}