Generalize the and-icmp-select instcombine further by allowing selects of the form
(x & 2^n) ? 2^m+C : C
we can offset both arms by C to get the "(x & 2^n) ? 2^m : 0" form, optimize the
select to a shift and apply the offset afterwards.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121609 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 6f0da3eb..82ce311 100644
--- a/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -457,10 +457,6 @@
if (!IC || !IC->isEquality())
return 0;
- // One of the select arms must be zero.
- if (!TrueVal->isZero() && !FalseVal->isZero())
- return 0;
-
if (ConstantInt *C = dyn_cast<ConstantInt>(IC->getOperand(1)))
if (!C->isZero())
return 0;
@@ -471,6 +467,24 @@
!match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS))))
return 0;
+ // If both select arms are non-zero see if we have a select of the form
+ // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
+ // for 'x ? 2^n : 0' and fix the thing up at the end.
+ ConstantInt *Offset = 0;
+ if (!TrueVal->isZero() && !FalseVal->isZero()) {
+ if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2())
+ Offset = FalseVal;
+ else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2())
+ Offset = TrueVal;
+ else
+ return 0;
+
+ // Adjust TrueVal and FalseVal to the offset.
+ TrueVal = ConstantInt::get(Builder->getContext(),
+ TrueVal->getValue() - Offset->getValue());
+ FalseVal = ConstantInt::get(Builder->getContext(),
+ FalseVal->getValue() - Offset->getValue());
+ }
// Make sure the mask in the 'and' and one of the select arms is a power of 2.
if (!AndRHS->getValue().isPowerOf2() ||
@@ -496,6 +510,10 @@
ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
if (ShouldNotVal)
V = Builder->CreateXor(V, ValC);
+
+ // Apply an offset if needed.
+ if (Offset)
+ V = Builder->CreateAdd(V, Offset);
return V;
}