[llvm] [RISCV] Fold shxadd into Xqcisls scaled load/store in RISCVMergeBaseOffset (PR #182221)

[Sam Elliott via llvm-commits]

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@@ -575,6 +576,114 @@ bool RISCVMergeBaseOffsetOpt::foldIntoMemoryOps(MachineInstr &Hi,
   return true;
 }
 
+// Try to fold sequences of the form:
+//   Hi/lo:    qc.e.li vreg1, s           -> qc.e.li vreg1, s+imm
+//   TailAdd:  shxadd vreg2, vreg3, vreg1 -> deleted
+//   Tail:     lx vreg4, imm(vreg2)       -> qc.lrx vreg4, vreg1, vreg3, (1/2/3)
+bool RISCVMergeBaseOffsetOpt::foldShxaddIntoScaledMemory(MachineInstr &Hi,
+                                                         MachineInstr &Lo) {
+  if (!ST->hasVendorXqcisls())
+    return false;
+
+  if (Hi.getOpcode() != RISCV::QC_E_LI)
+    return false;
+
+  Register BaseReg = Hi.getOperand(0).getReg();
+  if (!BaseReg.isVirtual() || !MRI->hasOneUse(BaseReg))
+    return false;
+
+  MachineInstr &ShxAdd = *MRI->use_instr_begin(BaseReg);
+  unsigned ShxOpc = ShxAdd.getOpcode();
+  if (ShxOpc != RISCV::SH1ADD && ShxOpc != RISCV::SH2ADD &&
+      ShxOpc != RISCV::SH3ADD)
+    return false;
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lenary wrote:

Can you add a TODO to support `qc.shladd`?

https://github.com/llvm/llvm-project/pull/182221