[llvm] [RISCV][VLOPT] Add support for Vector Fixed-Point Arithmetic Instructions (PR #126483)

[Luke Lau via llvm-commits]

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@@ -1173,8 +1201,16 @@ bool RISCVVLOptimizer::isCandidate(const MachineInstr &MI) const {
   const MCInstrDesc &Desc = MI.getDesc();
   if (!RISCVII::hasVLOp(Desc.TSFlags) || !RISCVII::hasSEWOp(Desc.TSFlags))
     return false;
-  if (MI.getNumDefs() != 1)
+
+  if (MI.getNumExplicitDefs() != 1)
+    return false;
+
+  // Some instructions have implicit defs e.g. $vxsat. If they might be read
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lukel97 wrote:

I quickly checked the qemu implementation, it seems to only set it for active elements: https://github.com/qemu/qemu/blob/04d3d0e9f54d4c42759f3810aa135ce314d98dc4/target/riscv/vector_helper.c#L2162-L2179

https://github.com/llvm/llvm-project/pull/126483