[llvm] [ConstraintElim] Tighten bounds using inequalities with constants. (PR #213049)

[Florian Hahn via llvm-commits]

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@@ -1781,6 +1786,47 @@ void ConstraintInfo::addFact(CmpInst::Predicate Pred, Value *A, Value *B,
   // If the Pred is eq/ne, also add the fact to signed system.
   if (CmpInst::isEquality(Pred))
     addFactImpl(Pred, A, B, NumIn, NumOut, DFSInStack, true);
+  if (Pred == CmpInst::ICMP_NE)
+    tightenBoundUsingNe(A, B, NumIn, NumOut, DFSInStack);
+}
+
+void ConstraintInfo::tightenBoundUsingNe(
+    Value *A, Value *B, unsigned NumIn, unsigned NumOut,
+    SmallVectorImpl<StackEntry> &DFSInStack) {
+  if (!isa<ConstantInt>(B) || !A->getType()->isIntegerTy())
+    return;
+
+  for (bool IsSigned : {false, true}) {
+    // In the unsigned system `A u>= 0` holds for every A, so getConstraint
+    // already turned `A != 0` into `A u> 0`.
+    if (!IsSigned && match(B, m_Zero()))
+      continue;
+
+    // Skip if there are any unknown variables.
+    const auto &Value2Index = getValue2Index(IsSigned);
+    if (any_of(decompose(A, *this, IsSigned, DL).Vars,
+               [&Value2Index](const DecompEntry &E) {
+                 return !Value2Index.contains(E.Variable);
+               }))
+      continue;
+
+    // If the system implies `A >= B` then together with `A != B` we get the
+    // strict `A > B`; symmetrically `A <= B` becomes `A < B`.
+    for (CmpInst::Predicate NonStrict :
+         {IsSigned ? CmpInst::ICMP_SGE : CmpInst::ICMP_UGE,
+          IsSigned ? CmpInst::ICMP_SLE : CmpInst::ICMP_ULE}) {
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fhahn wrote:

done thanks

https://github.com/llvm/llvm-project/pull/213049