[PATCH] D159203: [InstCombine] Fold (A/-B)==(A/B) to (A/B)==0

[Marc Auberer via Phabricator via llvm-commits]

marcauberer updated this revision to Diff 555587.
marcauberer added a comment.

Rebase onto ValueTracking change


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D159203/new/

https://reviews.llvm.org/D159203

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
  llvm/test/Transforms/InstCombine/icmp-sdiv-sdiv.ll


Index: llvm/test/Transforms/InstCombine/icmp-sdiv-sdiv.ll
===================================================================
--- llvm/test/Transforms/InstCombine/icmp-sdiv-sdiv.ll
+++ llvm/test/Transforms/InstCombine/icmp-sdiv-sdiv.ll
@@ -9,10 +9,8 @@
 ; CHECK-LABEL: @icmp_sdiv_sdiv_normal_i8(
 ; CHECK-NEXT:    [[PRECOND:%.*]] = icmp ne i8 [[C:%.*]], -128
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[PRECOND]])
-; CHECK-NEXT:    [[NEGC:%.*]] = sub i8 0, [[C]]
-; CHECK-NEXT:    [[D1:%.*]] = sdiv i8 [[X:%.*]], [[NEGC]]
-; CHECK-NEXT:    [[D2:%.*]] = sdiv i8 [[X]], [[C]]
-; CHECK-NEXT:    [[C:%.*]] = icmp eq i8 [[D1]], [[D2]]
+; CHECK-NEXT:    [[D2:%.*]] = sdiv i8 [[X:%.*]], [[C]]
+; CHECK-NEXT:    [[C:%.*]] = icmp eq i8 [[D2]], 0
 ; CHECK-NEXT:    ret i1 [[C]]
 ;
   %precond = icmp ne i8 %C, -128
@@ -28,10 +26,8 @@
 ; CHECK-LABEL: @icmp_sdiv_sdiv_normal_i64(
 ; CHECK-NEXT:    [[PRECOND:%.*]] = icmp ne i64 [[C:%.*]], -9223372036854775808
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[PRECOND]])
-; CHECK-NEXT:    [[NEGC:%.*]] = sub i64 0, [[C]]
-; CHECK-NEXT:    [[D1:%.*]] = sdiv i64 [[X:%.*]], [[NEGC]]
-; CHECK-NEXT:    [[D2:%.*]] = sdiv i64 [[X]], [[C]]
-; CHECK-NEXT:    [[C:%.*]] = icmp eq i64 [[D1]], [[D2]]
+; CHECK-NEXT:    [[D2:%.*]] = sdiv i64 [[X:%.*]], [[C]]
+; CHECK-NEXT:    [[C:%.*]] = icmp eq i64 [[D2]], 0
 ; CHECK-NEXT:    ret i1 [[C]]
 ;
   %precond = icmp ne i64 %C, -9223372036854775808
Index: llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -5164,6 +5164,23 @@
     return new ICmpInst(Pred, OtherVal, Constant::getNullValue(A->getType()));
   }
 
+  // ((A / -B) == (A / B)) -> ((A / B) == 0)
+  // if known A != INT_MIN or B != INT_MIN
+  {
+    const unsigned OpWidth = Op0->getType()->getScalarSizeInBits();
+    APInt SignedMinValue = APInt::getSignedMinValue(OpWidth);
+    Constant *MinInt = ConstantInt::get(Op0->getType(), SignedMinValue);
+    if (match(Op0, m_OneUse(m_SDiv(m_Value(A), m_OneUse(m_Neg(m_Value(B)))))) &&
+        match(Op1, m_SDiv(m_Specific(A), m_Specific(B)))) {
+      // Check if A is known to be != INT_MIN
+      if (isKnownNonEqual(A, MinInt, DL, &AC, &I, &DT, true))
+        return new ICmpInst(Pred, Op1, Constant::getNullValue(A->getType()));
+      // Check if B is known to be != INT_MIN
+      if (isKnownNonEqual(B, MinInt, DL, &AC, &I, &DT, true))
+        return new ICmpInst(Pred, Op1, Constant::getNullValue(A->getType()));
+    }
+  }
+
   // (X&Z) == (Y&Z) -> (X^Y) & Z == 0
   if (match(Op0, m_OneUse(m_And(m_Value(A), m_Value(B)))) &&
       match(Op1, m_OneUse(m_And(m_Value(C), m_Value(D))))) {


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