[InstCombine] foldICmpWithLowBitMaskedVal(): handle uncanonical ((1 << y)+(-1)) mask

Summary:
Same as to D52146.
`((1 << y)+(-1))` is simply non-canoniacal version of `~(-1 << y)`: https://rise4fun.com/Alive/0vl
We can not canonicalize it due to the extra uses. But we can handle it here.

Reviewers: spatel, craig.topper, RKSimon

Reviewed By: spatel

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D52147

llvm-svn: 342547

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index f06a0e83c9b..c6294d173d9 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2887,6 +2887,7 @@ Instruction *InstCombiner::foldICmpInstWithConstantNotInt(ICmpInst &I) {
 /// Where Mask is some pattern that produces all-ones in low bits:
 ///    (-1 >> y)
 ///   ~(-1 << y)
+///    ((1 << y) + (-1))    <- non-canonical, has extra uses
 /// The Mask can be a constant, too.
 /// For some predicates, the operands are commutative.
 /// For others, x can only be on a specific side.
@@ -2894,8 +2895,10 @@ static Value *foldICmpWithLowBitMaskedVal(ICmpInst &I,
                                           InstCombiner::BuilderTy &Builder) {
   ICmpInst::Predicate SrcPred;
   Value *X, *M;
-  auto m_VariableMask = m_CombineOr(m_Not(m_Shl(m_AllOnes(), m_Value())),
-                                    m_LShr(m_AllOnes(), m_Value()));
+  auto m_VariableMask =
+      m_CombineOr(m_CombineOr(m_Not(m_Shl(m_AllOnes(), m_Value())),
+                              m_Add(m_Shl(m_One(), m_Value()), m_AllOnes())),
+                  m_LShr(m_AllOnes(), m_Value()));
   auto m_Mask = m_CombineOr(m_VariableMask, m_LowBitMask());
   if (!match(&I, m_c_ICmp(SrcPred,
                           m_c_And(m_CombineAnd(m_Mask, m_Value(M)), m_Value(X)),