Fix PR6165. The bug was that LHSKnownZero was being and'd with DemandedMask
when it should have been and'd with LowBits. Fix that and while there beef
up the logic in the case of a negative LHS.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94745 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 74a1b68..ec1ed66 100644
--- a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -681,10 +681,19 @@
LHSKnownZero, LHSKnownOne, Depth+1))
return I;
- if (LHSKnownZero[BitWidth-1] || ((LHSKnownZero & LowBits) == LowBits))
- LHSKnownZero |= ~LowBits;
+ // The low bits of LHS are unchanged by the srem.
+ KnownZero |= LHSKnownZero & LowBits;
+ KnownOne |= LHSKnownOne & LowBits;
- KnownZero |= LHSKnownZero & DemandedMask;
+ // If LHS is non-negative or has all low bits zero, then the upper bits
+ // are all zero.
+ if (LHSKnownZero[BitWidth-1] || ((LHSKnownZero & LowBits) == LowBits))
+ KnownZero |= ~LowBits;
+
+ // If LHS is negative and not all low bits are zero, then the upper bits
+ // are all one.
+ if (LHSKnownOne[BitWidth-1] && ((LHSKnownOne & LowBits) != 0))
+ KnownOne |= ~LowBits;
assert(!(KnownZero & KnownOne) && "Bits known to be one AND zero?");
}