[InstSimplify] simplify power-of-2 (single bit set) sequences
As discussed in PR42314:
https://bugs.llvm.org/show_bug.cgi?id=42314
Improving the canonicalization for these patterns:
rL363956
...means we should adjust/enhance the related simplification.
https://rise4fun.com/Alive/w1cp
Name: isPow2 or zero
%x = and i32 %xx, 2048
%a = add i32 %x, -1
%r = and i32 %a, %x
=>
%r = i32 0
llvm-svn: 363997
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index ba76c5b..ce0b8a0 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1845,6 +1845,16 @@
return Op1;
}
+ // This is a similar pattern used for checking if a value is a power-of-2:
+ // (A - 1) & A --> 0 (if A is a power-of-2 or 0)
+ // A & (A - 1) --> 0 (if A is a power-of-2 or 0)
+ if (match(Op0, m_Add(m_Specific(Op1), m_AllOnes())) &&
+ isKnownToBeAPowerOfTwo(Op1, Q.DL, /*OrZero*/ true, 0, Q.AC, Q.CxtI, Q.DT))
+ return Constant::getNullValue(Op1->getType());
+ if (match(Op1, m_Add(m_Specific(Op0), m_AllOnes())) &&
+ isKnownToBeAPowerOfTwo(Op0, Q.DL, /*OrZero*/ true, 0, Q.AC, Q.CxtI, Q.DT))
+ return Constant::getNullValue(Op0->getType());
+
if (Value *V = simplifyAndOrOfCmps(Q, Op0, Op1, true))
return V;