[llvm] [RISCV] Fold LI 1 / SLLI into BSETI during i64 materialization (PR #142348)

[Piotr Fusik via llvm-commits]

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@@ -353,6 +353,13 @@ InstSeq generateInstSeq(int64_t Val, const MCSubtargetInfo &STI) {
       } while (Hi != 0);
       Res = TmpSeq;
     }
+
+    // Fold LI 1 + SLLI into BSETI.
+    if (Res[0].getOpcode() == RISCV::ADDI && Res[0].getImm() == 1 &&
+        Res[1].getOpcode() == RISCV::SLLI) {
+      Res.erase(Res.begin()); // Remove ADDI.
+      Res.front() = Inst(RISCV::BSETI, Res.front().getImm()); // Patch SLLI.
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pfusik wrote:

Another option would be to add `setOpcode()`.

https://github.com/llvm/llvm-project/pull/142348