[llvm] r371718 - [InstSimplify] simplifyUnsignedRangeCheck(): handle more cases (PR43251)

[Roman Lebedev via llvm-commits]

Author: lebedevri
Date: Thu Sep 12 02:26:17 2019
New Revision: 371718

URL: http://llvm.org/viewvc/llvm-project?rev=371718&view=rev
Log:
[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

Modified:
    llvm/trunk/lib/Analysis/InstructionSimplify.cpp
    llvm/trunk/test/Transforms/InstSimplify/result-of-usub-by-nonzero-is-non-zero-and-no-overflow.ll

Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=371718&r1=371717&r2=371718&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Thu Sep 12 02:26:17 2019
@@ -1381,6 +1381,26 @@ static Value *simplifyUnsignedRangeCheck
     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))
     ;

Modified: llvm/trunk/test/Transforms/InstSimplify/result-of-usub-by-nonzero-is-non-zero-and-no-overflow.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/result-of-usub-by-nonzero-is-non-zero-and-no-overflow.ll?rev=371718&r1=371717&r2=371718&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/result-of-usub-by-nonzero-is-non-zero-and-no-overflow.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/result-of-usub-by-nonzero-is-non-zero-and-no-overflow.ll Thu Sep 12 02:26:17 2019
@@ -10,9 +10,7 @@ define i1 @t0(i64 %base, i64* nonnull %o
 ; CHECK-NEXT:    [[OFFSET:%.*]] = ptrtoint i64* [[OFFSETPTR:%.*]] to i64
 ; CHECK-NEXT:    [[ADJUSTED:%.*]] = sub i64 [[BASE:%.*]], [[OFFSET]]
 ; CHECK-NEXT:    [[NO_UNDERFLOW:%.*]] = icmp uge i64 [[ADJUSTED]], [[BASE]]
-; CHECK-NEXT:    [[NOT_NULL:%.*]] = icmp ne i64 [[ADJUSTED]], 0
-; CHECK-NEXT:    [[R:%.*]] = and i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 [[NO_UNDERFLOW]]
 ;
   %offset = ptrtoint i64* %offsetptr to i64
 
@@ -28,9 +26,7 @@ define i1 @t1(i64 %base, i64* nonnull %o
 ; CHECK-NEXT:    [[OFFSET:%.*]] = ptrtoint i64* [[OFFSETPTR:%.*]] to i64
 ; CHECK-NEXT:    [[ADJUSTED:%.*]] = sub i64 [[BASE:%.*]], [[OFFSET]]
 ; CHECK-NEXT:    [[NO_UNDERFLOW:%.*]] = icmp ult i64 [[ADJUSTED]], [[BASE]]
-; CHECK-NEXT:    [[NOT_NULL:%.*]] = icmp eq i64 [[ADJUSTED]], 0
-; CHECK-NEXT:    [[R:%.*]] = or i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 [[NO_UNDERFLOW]]
 ;
   %offset = ptrtoint i64* %offsetptr to i64
 
@@ -46,9 +42,7 @@ define i1 @t2_commutative(i64 %base, i64
 ; CHECK-NEXT:    [[OFFSET:%.*]] = ptrtoint i64* [[OFFSETPTR:%.*]] to i64
 ; CHECK-NEXT:    [[ADJUSTED:%.*]] = sub i64 [[BASE:%.*]], [[OFFSET]]
 ; CHECK-NEXT:    [[NO_UNDERFLOW:%.*]] = icmp ule i64 [[BASE]], [[ADJUSTED]]
-; CHECK-NEXT:    [[NOT_NULL:%.*]] = icmp ne i64 [[ADJUSTED]], 0
-; CHECK-NEXT:    [[R:%.*]] = and i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 [[NO_UNDERFLOW]]
 ;
   %offset = ptrtoint i64* %offsetptr to i64
 
@@ -64,9 +58,7 @@ define i1 @t3_commutative(i64 %base, i64
 ; CHECK-NEXT:    [[OFFSET:%.*]] = ptrtoint i64* [[OFFSETPTR:%.*]] to i64
 ; CHECK-NEXT:    [[ADJUSTED:%.*]] = sub i64 [[BASE:%.*]], [[OFFSET]]
 ; CHECK-NEXT:    [[NO_UNDERFLOW:%.*]] = icmp ugt i64 [[BASE]], [[ADJUSTED]]
-; CHECK-NEXT:    [[NOT_NULL:%.*]] = icmp eq i64 [[ADJUSTED]], 0
-; CHECK-NEXT:    [[R:%.*]] = or i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 [[NO_UNDERFLOW]]
 ;
   %offset = ptrtoint i64* %offsetptr to i64