[InstSimplify] simplifyUnsignedRangeCheck(): handle more cases (PR43251)

Summary:
I don't have a direct motivational case for this,
but it would be good to have this for completeness/symmetry.

This pattern is basically the motivational pattern from
https://bugs.llvm.org/show_bug.cgi?id=43251
but with different predicate that requires that the offset is non-zero.

The completeness bit comes from the fact that a similar pattern (offset != zero)
will be needed for https://bugs.llvm.org/show_bug.cgi?id=43259,
so it'd seem to be good to not overlook very similar patterns..

Proofs: https://rise4fun.com/Alive/21b

Also, there is something odd with `isKnownNonZero()`, if the non-zero
knowledge was specified as an assumption, it didn't pick it up (PR43267)

Reviewers: spatel, nikic, xbolva00

Reviewed By: spatel

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67411

llvm-svn: 371718

1 files changed, 20 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 5e3a22aba96..defa3c3ea56 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1381,6 +1381,26 @@ static Value *simplifyUnsignedRangeCheck(ICmpInst *ZeroICmp,
     return nullptr;
 
   ICmpInst::Predicate UnsignedPred;
+
+  // Y = (A - B);  Y >= A && Y != 0  --> Y >= A  iff B != 0
+  // Y = (A - B);  Y <  A || Y == 0  --> Y <  A  iff B != 0
+  Value *A, *B;
+  if (match(Y, m_Sub(m_Value(A), m_Value(B))) &&
+      match(UnsignedICmp,
+            m_c_ICmp(UnsignedPred, m_Specific(Y), m_Specific(A)))) {
+    if (UnsignedICmp->getOperand(0) != Y)
+      UnsignedPred = ICmpInst::getSwappedPredicate(UnsignedPred);
+
+    if (UnsignedPred == ICmpInst::ICMP_UGE && IsAnd &&
+        EqPred == ICmpInst::ICMP_NE &&
+        isKnownNonZero(B, Q.DL, /*Depth=*/0, Q.AC, Q.CxtI, Q.DT))
+      return UnsignedICmp;
+    if (UnsignedPred == ICmpInst::ICMP_ULT && !IsAnd &&
+        EqPred == ICmpInst::ICMP_EQ &&
+        isKnownNonZero(B, Q.DL, /*Depth=*/0, Q.AC, Q.CxtI, Q.DT))
+      return UnsignedICmp;
+  }
+
   if (match(UnsignedICmp, m_ICmp(UnsignedPred, m_Value(X), m_Specific(Y))) &&
       ICmpInst::isUnsigned(UnsignedPred))
     ;