[llvm] [SLP]Consider (f)sub, being operand of llvm.(f)abs/icmp eq/ne 0, commutative. (PR #86196)

[Simon Pilgrim via llvm-commits]

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@@ -305,7 +305,32 @@ static bool isCommutative(Instruction *I) {
   if (auto *Cmp = dyn_cast<CmpInst>(I))
     return Cmp->isCommutative();
   if (auto *BO = dyn_cast<BinaryOperator>(I))
-    return BO->isCommutative();
+    return BO->isCommutative() ||
+           (BO->getOpcode() == Instruction::Sub &&
+            !BO->hasNUsesOrMore(UsesLimit) &&
+            all_of(BO->uses(),
+                   [](const Use &U) {
+                     // Commutative, if icmp eq/ne sub, 0
+                     ICmpInst::Predicate Pred;
+                     if (match(U.getUser(),
+                               m_ICmp(Pred, m_Specific(U.get()), m_Zero())) &&
+                         (Pred == ICmpInst::ICMP_EQ ||
+                          Pred == ICmpInst::ICMP_NE))
+                       return true;
+                     // Commutative, if abs(sub, flag).
+                     if (U.getOperandNo() != 0)
+                       return false;
+                     const auto *IC = dyn_cast<IntrinsicInst>(U.getUser());
+                     return IC && IC->getIntrinsicID() == Intrinsic::abs;
+                   })) ||
+           (BO->getOpcode() == Instruction::FSub &&
+            !BO->hasNUsesOrMore(UsesLimit) &&
+            all_of(BO->uses(), [](const Use &U) {
+              if (U.getOperandNo() != 0)
+                return false;
+              const auto *IC = dyn_cast<IntrinsicInst>(U.getUser());
+              return IC && IC->getIntrinsicID() == Intrinsic::fabs;
+            }));
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RKSimon wrote:

OK.

https://github.com/llvm/llvm-project/pull/86196