[llvm] [InstCombine] Simplify `(X / C0) * C1 + (X % C0) * C2` to `(X / C0) * (C1 - C2 * C0) + X * C2` (PR #76285)

[Yingwei Zheng via llvm-commits]

================
@@ -1161,6 +1163,33 @@ Value *InstCombinerImpl::SimplifyAddWithRemainder(BinaryOperator &I) {
     }
   }
 
+  // Match I = (X / C0) * C1 + (X % C0) * C2
+  Value *Div, *Rem;
+  APInt C1, C2;
+  if (!LHS->hasOneUse() || !MatchMul(LHS, Div, C1))
+    Div = LHS, C1 = APInt(I.getType()->getScalarSizeInBits(), 1);
+  if (!RHS->hasOneUse() || !MatchMul(RHS, Rem, C2))
+    Rem = RHS, C2 = APInt(I.getType()->getScalarSizeInBits(), 1);
+  if (match(Div, m_IRem(m_Value(), m_Value()))) {
+    std::swap(Div, Rem);
+    std::swap(C1, C2);
+  }
+  Value *DivOpV;
+  APInt DivOpC;
+  if (MatchRem(Rem, X, C0, IsSigned) &&
+      MatchDiv(Div, DivOpV, DivOpC, IsSigned) && X == DivOpV && C0 == DivOpC) {
+    if (!isGuaranteedNotToBeUndef(X, &AC, &I, &DT))
----------------
dtcxzyw wrote:

Done.

https://github.com/llvm/llvm-project/pull/76285