[llvm] RISCV: Use m_GImplicitDef instead of getVRegDef + opcode check (PR #216514)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-globalisel

Author: Matt Arsenault (arsenm)

<details>
<summary>Changes</summary>

Co-authored-by: Claude (Opus 4.8) <noreply@<!-- -->anthropic.com>

---
Full diff: https://github.com/llvm/llvm-project/pull/216514.diff


1 Files Affected:

- (modified) llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp (+3-2) 


``````````diff
diff --git a/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp b/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
index c5459d862b03f..22f60dc0c1c24 100644
--- a/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
+++ b/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
@@ -17,6 +17,7 @@
 #include "llvm/CodeGen/GlobalISel/GIMatchTableExecutor.h"
 #include "llvm/CodeGen/GlobalISel/GenericMachineInstrs.h"
 #include "llvm/CodeGen/GlobalISel/LegalizerHelper.h"
+#include "llvm/CodeGen/GlobalISel/MIPatternMatch.h"
 #include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
 #include "llvm/CodeGen/MachineConstantPool.h"
 #include "llvm/CodeGen/MachineJumpTableInfo.h"
@@ -33,6 +34,7 @@
 using namespace llvm;
 using namespace LegalityPredicates;
 using namespace LegalizeMutations;
+using namespace MIPatternMatch;
 
 static LegalityPredicate
 typeIsLegalIntOrFPVec(unsigned TypeIdx,
@@ -1311,8 +1313,7 @@ bool RISCVLegalizerInfo::legalizeInsertSubvector(MachineInstr &MI,
   LLT BigTy = MRI.getType(BigVec);
   LLT LitTy = MRI.getType(LitVec);
 
-  if (Idx == 0 &&
-      MRI.getVRegDef(BigVec)->getOpcode() == TargetOpcode::G_IMPLICIT_DEF)
+  if (Idx == 0 && mi_match(BigVec, MRI, m_GImplicitDef()))
     return true;
 
   // We don't have the ability to slide mask vectors up indexed by their i1

``````````

</details>


https://github.com/llvm/llvm-project/pull/216514