[llvm] [RISCV] Generalize the (ADD (SLLI X, 32), X) special case in constant… (PR #66931)

[Philip Reames via llvm-commits]

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@@ -195,29 +195,24 @@ static SDValue selectImm(SelectionDAG *CurDAG, const SDLoc &DL, const MVT VT,
   RISCVMatInt::InstSeq Seq =
       RISCVMatInt::generateInstSeq(Imm, Subtarget.getFeatureBits());
 
-  // See if we can create this constant as (ADD (SLLI X, 32), X) where X is at
+  // See if we can create this constant as (ADD (SLLI X, C), X) where X is at
   // worst an LUI+ADDIW. This will require an extra register, but avoids a
   // constant pool.
   // If we have Zba we can use (ADD_UW X, (SLLI X, 32)) to handle cases where
   // low and high 32 bits are the same and bit 31 and 63 are set.
   if (Seq.size() > 3) {
-    int64_t LoVal = SignExtend64<32>(Imm);
-    int64_t HiVal = SignExtend64<32>(((uint64_t)Imm - (uint64_t)LoVal) >> 32);
-    if (LoVal == HiVal ||
-        (Subtarget.hasStdExtZba() && Lo_32(Imm) == Hi_32(Imm))) {
-      RISCVMatInt::InstSeq SeqLo =
-          RISCVMatInt::generateInstSeq(LoVal, Subtarget.getFeatureBits());
-      if ((SeqLo.size() + 2) < Seq.size()) {
-        SDValue Lo = selectImmSeq(CurDAG, DL, VT, SeqLo);
-
-        SDValue SLLI = SDValue(
-            CurDAG->getMachineNode(RISCV::SLLI, DL, VT, Lo,
-                                   CurDAG->getTargetConstant(32, DL, VT)),
-            0);
-        // Prefer ADD when possible.
-        unsigned AddOpc = (LoVal == HiVal) ? RISCV::ADD : RISCV::ADD_UW;
-        return SDValue(CurDAG->getMachineNode(AddOpc, DL, VT, Lo, SLLI), 0);
-      }
+    unsigned ShiftAmt, AddOpc;
+    RISCVMatInt::InstSeq SeqLo = RISCVMatInt::generateTwoRegInstSeq(
+        Imm, Subtarget.getFeatureBits(), ShiftAmt, AddOpc);
+    if (!SeqLo.empty() && (SeqLo.size() + 2) < Seq.size()) {
+      SDValue Lo = selectImmSeq(CurDAG, DL, VT, SeqLo);
+
+      SDValue SLLI = SDValue(
+          CurDAG->getMachineNode(RISCV::SLLI, DL, VT, Lo,
+                                 CurDAG->getTargetConstant(ShiftAmt, DL, VT)),
+          0);
+      // Prefer ADD when possible.
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preames wrote:

Kill the oddly placed comment

https://github.com/llvm/llvm-project/pull/66931