[llvm] [RISCV] Move RISCVInsertVSETVLI to after phi elimination (PR #91440)

[Luke Lau via llvm-commits]

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@@ -519,28 +527,31 @@ class VSETVLIInfo {
   bool getTailAgnostic() const { return TailAgnostic; }
   bool getMaskAgnostic() const { return MaskAgnostic; }
 
-  bool hasNonZeroAVL() const {
+  bool hasNonZeroAVL(const LiveIntervals *LIS) const {
     if (hasAVLImm())
       return getAVLImm() > 0;
-    if (hasAVLReg())
-      return isNonZeroLoadImmediate(getAVLDefMI());
+    if (hasAVLReg()) {
+      if (auto *DefMI = LIS->getInstructionFromIndex(getAVLVNInfo()->def))
+        return isNonZeroLoadImmediate(*DefMI);
+    }
     if (hasAVLVLMAX())
       return true;
     if (hasAVLIgnored())
       return false;
     return false;
   }
 
-  bool hasEquallyZeroAVL(const VSETVLIInfo &Other) const {
+  bool hasEquallyZeroAVL(const VSETVLIInfo &Other,
+                         const LiveIntervals *LIS) const {
     if (hasSameAVL(Other))
       return true;
-    return (hasNonZeroAVL() && Other.hasNonZeroAVL());
+    return (hasNonZeroAVL(LIS) && Other.hasNonZeroAVL(LIS));
   }
 
   bool hasSameAVL(const VSETVLIInfo &Other) const {
     if (hasAVLReg() && Other.hasAVLReg())
-      return AVLRegDef.DefMI == Other.AVLRegDef.DefMI &&
-             AVLRegDef.DefReg == Other.AVLRegDef.DefReg;
+      return getAVLVNInfo()->id == Other.getAVLVNInfo()->id &&
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lukel97 wrote:

I didn't notice any difference between using id and def, but is it possible for two different phi nodes to end up with the same def after phi elimination? I.e. both would point to the start of the block

https://github.com/llvm/llvm-project/pull/91440