[llvm] [InstCombine] Fold `icmp pred X + K, Y -> icmp pred2 X, Y` if both X and Y is divisible by K (PR #147130)

[Nikita Popov via llvm-commits]

================
@@ -5278,66 +5287,62 @@ Instruction *InstCombinerImpl::foldICmpBinOp(ICmpInst &I,
     return new ICmpInst(Pred, Y, Z);
   }
 
-  // icmp slt (A + -1), Op1 -> icmp sle A, Op1
-  if (A && NoOp0WrapProblem && Pred == CmpInst::ICMP_SLT &&
-      match(B, m_AllOnes()))
-    return new ICmpInst(CmpInst::ICMP_SLE, A, Op1);
-
-  // icmp sge (A + -1), Op1 -> icmp sgt A, Op1
-  if (A && NoOp0WrapProblem && Pred == CmpInst::ICMP_SGE &&
-      match(B, m_AllOnes()))
-    return new ICmpInst(CmpInst::ICMP_SGT, A, Op1);
-
-  // icmp sle (A + 1), Op1 -> icmp slt A, Op1
-  if (A && NoOp0WrapProblem && Pred == CmpInst::ICMP_SLE && match(B, m_One()))
-    return new ICmpInst(CmpInst::ICMP_SLT, A, Op1);
-
-  // icmp sgt (A + 1), Op1 -> icmp sge A, Op1
-  if (A && NoOp0WrapProblem && Pred == CmpInst::ICMP_SGT && match(B, m_One()))
-    return new ICmpInst(CmpInst::ICMP_SGE, A, Op1);
+  if (ICmpInst::isRelational(Pred)) {
+    // Return if both X and Y is divisible by Z/-Z.
+    // TODO: Generalize to check if (X - Y) is divisible by Z/-Z.
+    auto ShareCommonDivisor = [&Q](Value *X, Value *Y, Value *Z,
+                                   bool IsNegative) -> bool {
+      const APInt *OffsetC;
+      if (!match(Z, m_APInt(OffsetC)))
+        return false;
 
-  // icmp sgt Op0, (C + -1) -> icmp sge Op0, C
-  if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SGT &&
-      match(D, m_AllOnes()))
-    return new ICmpInst(CmpInst::ICMP_SGE, Op0, C);
+      // Fast path for Z == 1/-1.
+      if (IsNegative ? OffsetC->isAllOnes() : OffsetC->isOne())
+        return true;
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nikic wrote:

Okay, I see you have a fast-path here, but I think isMultipleOf() should also handle it directly, for future users.

https://github.com/llvm/llvm-project/pull/147130