[InstCombine] Handle commuted pattern for ((X s/ C1) << C2) + X (llvm#121737)

Closes llvm#121700

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -1326,6 +1326,18 @@ Instruction *InstCombinerImpl::foldAddLikeCommutative(Value *LHS, Value *RHS,
     R->setHasNoUnsignedWrap(NUWOut);
     return R;
   }
+
+  // ((X s/ C1) << C2) + X => X s% -C1 where -C1 is 1 << C2
+  const APInt *C1, *C2;
+  if (match(LHS, m_Shl(m_SDiv(m_Specific(RHS), m_APInt(C1)), m_APInt(C2)))) {
+    APInt One(C2->getBitWidth(), 1);
+    APInt MinusC1 = -(*C1);
+    if (MinusC1 == (One << *C2)) {
+      Constant *NewRHS = ConstantInt::get(RHS->getType(), MinusC1);
+      return BinaryOperator::CreateSRem(RHS, NewRHS);
+    }
+  }
+
   return nullptr;
 }
 
@@ -1623,17 +1635,7 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
   // X % C0 + (( X / C0 ) % C1) * C0 => X % (C0 * C1)
   if (Value *V = SimplifyAddWithRemainder(I)) return replaceInstUsesWith(I, V);
 
-  // ((X s/ C1) << C2) + X => X s% -C1 where -C1 is 1 << C2
-  const APInt *C1, *C2;
-  if (match(LHS, m_Shl(m_SDiv(m_Specific(RHS), m_APInt(C1)), m_APInt(C2)))) {
-    APInt one(C2->getBitWidth(), 1);
-    APInt minusC1 = -(*C1);
-    if (minusC1 == (one << *C2)) {
-      Constant *NewRHS = ConstantInt::get(RHS->getType(), minusC1);
-      return BinaryOperator::CreateSRem(RHS, NewRHS);
-    }
-  }
-
+  const APInt *C1;
   // (A & 2^C1) + A => A & (2^C1 - 1) iff bit C1 in A is a sign bit
   if (match(&I, m_c_Add(m_And(m_Value(A), m_APInt(C1)), m_Deferred(A))) &&
       C1->isPowerOf2() && (ComputeNumSignBits(A) > C1->countl_zero())) {

llvm/test/Transforms/InstCombine/add-shl-sdiv-to-srem.ll

@@ -12,6 +12,17 @@ define i8 @add-shl-sdiv-scalar0(i8 %x) {
   ret i8 %rz
 }
 
+define i8 @add-shl-sdiv-scalar0_commuted(i8 %x) {
+; CHECK-LABEL: @add-shl-sdiv-scalar0_commuted(
+; CHECK-NEXT:    [[RZ:%.*]] = srem i8 [[X:%.*]], 4
+; CHECK-NEXT:    ret i8 [[RZ]]
+;
+  %sd = sdiv i8 %x, -4
+  %sl = shl i8 %sd, 2
+  %rz = add i8 %x, %sl
+  ret i8 %rz
+}
+
 define i8 @add-shl-sdiv-scalar1(i8 %x) {
 ; CHECK-LABEL: @add-shl-sdiv-scalar1(
 ; CHECK-NEXT:    [[RZ:%.*]] = srem i8 [[X:%.*]], 64