[llvm] [ValueTracking] Analyze `Select` in `isKnownNonEqual`. (PR #68427)

[Mikhail Gudim via llvm-commits]

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@@ -3112,6 +3112,39 @@ static bool isNonEqualPHIs(const PHINode *PN1, const PHINode *PN2,
   return true;
 }
 
+static bool isNonEqualSelect(const Value *V1, const Value *V2, unsigned Depth,
+                             const SimplifyQuery &Q) {
+  const SelectInst *SI1 = dyn_cast<SelectInst>(V1);
+  if (!SI1)
+    return false;
+
+  if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2)) {
+    const Value *TVal1 = nullptr;
+    const Value *TVal2 = nullptr;
+    const Value *FVal1 = nullptr;
+    const Value *FVal2 = nullptr;
+    const Value *Cond1 = SI1->getCondition();
+    const Value *Cond2 = SI2->getCondition();
+    if (Cond1 == Cond2) {
+      TVal1 = SI1->getTrueValue();
+      TVal2 = SI2->getTrueValue();
+      FVal1 = SI1->getFalseValue();
+      FVal2 = SI2->getFalseValue();
+    }
+    if (match(Cond1, m_Not(m_Specific(Cond2)))) {
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mgudim wrote:

Did I understand correctly: you mean we could have something like `%Cond1 = icmp sle %x, 10` and `%Cond2 = icmp sgt %x, 10`, so no explicit `xor, -1` between the two, but two are actually always opposite. Thanks, very good point!

Let me see if there is some API for that.

https://github.com/llvm/llvm-project/pull/68427