[InstSimplify] simplifyUnsignedRangeCheck(): handle few tautological cases (PR43251)

Summary:
This is split off from D67356, since these cases produce a constant,
no real need to keep them in instcombine.

Alive proofs:
https://rise4fun.com/Alive/u7Fk
https://rise4fun.com/Alive/4lV

https://bugs.llvm.org/show_bug.cgi?id=43251

Reviewers: spatel, nikic, xbolva00

Reviewed By: spatel

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67498

llvm-svn: 371921

1 files changed, 37 insertions, 16 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index defa3c3ea56..cfb37f49bcc 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1382,23 +1382,44 @@ static Value *simplifyUnsignedRangeCheck(ICmpInst *ZeroICmp,
 
   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;
+  // Y = (A - B);
+  if (match(Y, m_Sub(m_Value(A), m_Value(B)))) {
+    if (match(UnsignedICmp,
+              m_c_ICmp(UnsignedPred, m_Specific(A), m_Specific(B))) &&
+        ICmpInst::isUnsigned(UnsignedPred)) {
+      if (UnsignedICmp->getOperand(0) != A)
+        UnsignedPred = ICmpInst::getSwappedPredicate(UnsignedPred);
+
+      // A >=/<= B || (A - B) != 0  <-->  true
+      if ((UnsignedPred == ICmpInst::ICMP_UGE ||
+           UnsignedPred == ICmpInst::ICMP_ULE) &&
+          EqPred == ICmpInst::ICMP_NE && !IsAnd)
+        return ConstantInt::getTrue(UnsignedICmp->getType());
+      // A </> B && (A - B) == 0  <-->  false
+      if ((UnsignedPred == ICmpInst::ICMP_ULT ||
+           UnsignedPred == ICmpInst::ICMP_UGT) &&
+          EqPred == ICmpInst::ICMP_EQ && IsAnd)
+        return ConstantInt::getFalse(UnsignedICmp->getType());
+    }
+
+    // Given  Y = (A - B)
+    //   Y >= A && Y != 0  --> Y >= A  iff B != 0
+    //   Y <  A || Y == 0  --> Y <  A  iff B != 0
+    if (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))) &&