[RISCV][NFC] Match 3/5/9 * 3/5/9 * 2^N without a loop (#165547)

#158851 matches `3/5/9 * 3/5/9` with a `switch`.
Reuse it for the shifted case to improve compilation time.

Author: pfusik

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -16495,6 +16495,35 @@ static SDValue expandMulToAddOrSubOfShl(SDNode *N, SelectionDAG &DAG,
   return DAG.getNode(Op, DL, VT, Shift1, Shift2);
 }
 
+static SDValue getShlAddShlAdd(SDNode *N, SelectionDAG &DAG, unsigned ShX,
+                               unsigned ShY) {
+  SDLoc DL(N);
+  EVT VT = N->getValueType(0);
+  SDValue X = N->getOperand(0);
+  SDValue Mul359 = DAG.getNode(RISCVISD::SHL_ADD, DL, VT, X,
+                               DAG.getConstant(ShY, DL, VT), X);
+  return DAG.getNode(RISCVISD::SHL_ADD, DL, VT, Mul359,
+                     DAG.getConstant(ShX, DL, VT), Mul359);
+}
+
+static SDValue expandMulToShlAddShlAdd(SDNode *N, SelectionDAG &DAG,
+                                       uint64_t MulAmt) {
+  switch (MulAmt) {
+  case 5 * 3:
+    return getShlAddShlAdd(N, DAG, 2, 1);
+  case 9 * 3:
+    return getShlAddShlAdd(N, DAG, 3, 1);
+  case 5 * 5:
+    return getShlAddShlAdd(N, DAG, 2, 2);
+  case 9 * 5:
+    return getShlAddShlAdd(N, DAG, 3, 2);
+  case 9 * 9:
+    return getShlAddShlAdd(N, DAG, 3, 3);
+  default:
+    return SDValue();
+  }
+}
+
 // Try to expand a scalar multiply to a faster sequence.
 static SDValue expandMul(SDNode *N, SelectionDAG &DAG,
                          TargetLowering::DAGCombinerInfo &DCI,
@@ -16524,18 +16553,17 @@ static SDValue expandMul(SDNode *N, SelectionDAG &DAG,
   if (Subtarget.hasVendorXqciac() && isInt<12>(CNode->getSExtValue()))
     return SDValue();
 
-  // WARNING: The code below is knowingly incorrect with regards to undef semantics.
-  // We're adding additional uses of X here, and in principle, we should be freezing
-  // X before doing so.  However, adding freeze here causes real regressions, and no
-  // other target properly freezes X in these cases either.
-  SDValue X = N->getOperand(0);
-
+  // WARNING: The code below is knowingly incorrect with regards to undef
+  // semantics.  We're adding additional uses of X here, and in principle, we
+  // should be freezing X before doing so.  However, adding freeze here causes
+  // real regressions, and no other target properly freezes X in these cases
+  // either.
   if (Subtarget.hasShlAdd(3)) {
+    SDValue X = N->getOperand(0);
     int Shift;
     if (int ShXAmount = isShifted359(MulAmt, Shift)) {
       // 3/5/9 * 2^N -> shl (shXadd X, X), N
       SDLoc DL(N);
-      SDValue X = N->getOperand(0);
       // Put the shift first if we can fold a zext into the shift forming
       // a slli.uw.
       if (X.getOpcode() == ISD::AND && isa<ConstantSDNode>(X.getOperand(1)) &&
@@ -16554,38 +16582,8 @@ static SDValue expandMul(SDNode *N, SelectionDAG &DAG,
     }
 
     // 3/5/9 * 3/5/9 -> shXadd (shYadd X, X), (shYadd X, X)
-    int ShX;
-    int ShY;
-    switch (MulAmt) {
-    case 3 * 5:
-      ShY = 1;
-      ShX = 2;
-      break;
-    case 3 * 9:
-      ShY = 1;
-      ShX = 3;
-      break;
-    case 5 * 5:
-      ShX = ShY = 2;
-      break;
-    case 5 * 9:
-      ShY = 2;
-      ShX = 3;
-      break;
-    case 9 * 9:
-      ShX = ShY = 3;
-      break;
-    default:
-      ShX = ShY = 0;
-      break;
-    }
-    if (ShX) {
-      SDLoc DL(N);
-      SDValue Mul359 = DAG.getNode(RISCVISD::SHL_ADD, DL, VT, X,
-                                   DAG.getConstant(ShY, DL, VT), X);
-      return DAG.getNode(RISCVISD::SHL_ADD, DL, VT, Mul359,
-                         DAG.getConstant(ShX, DL, VT), Mul359);
-    }
+    if (SDValue V = expandMulToShlAddShlAdd(N, DAG, MulAmt))
+      return V;
 
     // If this is a power 2 + 2/4/8, we can use a shift followed by a single
     // shXadd. First check if this a sum of two power of 2s because that's
@@ -16648,23 +16646,12 @@ static SDValue expandMul(SDNode *N, SelectionDAG &DAG,
       }
     }
 
-    for (uint64_t Divisor : {3, 5, 9}) {
-      if (MulAmt % Divisor != 0)
-        continue;
-      uint64_t MulAmt2 = MulAmt / Divisor;
-      // 3/5/9 * 3/5/9 * 2^N - In particular, this covers multiples
-      // of 25 which happen to be quite common.
-      if (int ShBAmount = isShifted359(MulAmt2, Shift)) {
-        SDLoc DL(N);
-        SDValue Mul359A =
-            DAG.getNode(RISCVISD::SHL_ADD, DL, VT, X,
-                        DAG.getConstant(Log2_64(Divisor - 1), DL, VT), X);
-        SDValue Mul359B =
-            DAG.getNode(RISCVISD::SHL_ADD, DL, VT, Mul359A,
-                        DAG.getConstant(ShBAmount, DL, VT), Mul359A);
-        return DAG.getNode(ISD::SHL, DL, VT, Mul359B,
-                           DAG.getConstant(Shift, DL, VT));
-      }
+    // 3/5/9 * 3/5/9 * 2^N - In particular, this covers multiples
+    // of 25 which happen to be quite common.
+    Shift = llvm::countr_zero(MulAmt);
+    if (SDValue V = expandMulToShlAddShlAdd(N, DAG, MulAmt >> Shift)) {
+      SDLoc DL(N);
+      return DAG.getNode(ISD::SHL, DL, VT, V, DAG.getConstant(Shift, DL, VT));
     }
   }