simplify/clarify control flow and improve comments, no functionality change.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@63480 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 186d837..f667945 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -817,22 +817,30 @@
if (isa<UndefValue>(V))
return 0;
return UndefValue::get(VTy);
- } else if (!V->hasOneUse()) { // Other users may use these bits.
- if (Depth != 0) { // Not at the root.
- // Just compute the KnownZero/KnownOne bits to simplify things downstream.
- ComputeMaskedBits(V, DemandedMask, KnownZero, KnownOne, Depth);
- return 0;
- }
- // If this is the root being simplified, allow it to have multiple uses,
- // just set the DemandedMask to all bits.
- DemandedMask = APInt::getAllOnesValue(BitWidth);
- } else if (Depth == 6) { // Limit search depth.
- return 0;
}
+ if (Depth == 6) // Limit search depth.
+ return 0;
+
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return 0; // Only analyze instructions.
-
+
+ // If there are multiple uses of this value and we aren't at the root, then
+ // we can't do any simplifications of the operands, because DemandedMask
+ // only reflects the bits demanded by *one* of the users.
+ if (Depth != 0 && !I->hasOneUse()) {
+ // Compute the KnownZero/KnownOne bits to simplify things downstream.
+ ComputeMaskedBits(I, DemandedMask, KnownZero, KnownOne, Depth);
+ return 0;
+ }
+
+ // If this is the root being simplified, allow it to have multiple uses,
+ // just set the DemandedMask to all bits so that we can try to simplify the
+ // operands. This allows visitTruncInst (for example) to simplify the
+ // operand of a trunc without duplicating all the logic below.
+ if (Depth == 0 && !V->hasOneUse())
+ DemandedMask = APInt::getAllOnesValue(BitWidth);
+
APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
APInt &RHSKnownZero = KnownZero, &RHSKnownOne = KnownOne;
switch (I->getOpcode()) {
@@ -6960,7 +6968,7 @@
Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1,
BinaryOperator &I) {
- bool isLeftShift = I.getOpcode() == Instruction::Shl;
+ bool isLeftShift = I.getOpcode() == Instruction::Shl;
// See if we can simplify any instructions used by the instruction whose sole
// purpose is to compute bits we don't care about.