[llvm] [RISCV] Use LiveIntervals to determine if AVL dominates when coalescing (PR #118285)

[Craig Topper via llvm-commits]

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@@ -1619,14 +1619,15 @@ bool RISCVInsertVSETVLI::canMutatePriorConfig(
     }
 
     auto &AVL = MI.getOperand(1);
-    auto &PrevAVL = PrevMI.getOperand(1);
 
-    // If the AVL is a register, we need to make sure MI's AVL dominates PrevMI.
-    // For now just check that PrevMI uses the same virtual register.
-    if (AVL.isReg() && AVL.getReg() != RISCV::X0 &&
-        (!MRI->hasOneDef(AVL.getReg()) || !PrevAVL.isReg() ||
-         PrevAVL.getReg() != AVL.getReg()))
-      return false;
+    // If the AVL is a register, we need to make sure its definition is the same
+    // at PrevMI as it was at MI.
+    if (AVL.isReg() && AVL.getReg() != RISCV::X0) {
+      VNInfo *VNI = getVNInfoFromReg(AVL.getReg(), MI, LIS);
+      VNInfo *PrevVNI = getVNInfoFromReg(AVL.getReg(), PrevMI, LIS);
+      if (!VNI || !PrevVNI || VNI->id != PrevVNI->id)
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topperc wrote:

Is comparing the `id` equivalent to comparing the VNInfo* pointers?

https://github.com/llvm/llvm-project/pull/118285