[llvm] [regalloc][LiveRegMatrix][AMDGPU] Fix LiveInterval dangling pointers in LiveRegMatrix. (PR #168556)

[Scott Linder via llvm-commits]

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@@ -290,6 +306,33 @@ Register LiveRegMatrix::getOneVReg(unsigned PhysReg) const {
   return MCRegister::NoRegister;
 }
 
+bool LiveRegMatrix::isValid() const {
+  // Build set of all valid LiveInterval pointers from LiveIntervals.
+  DenseSet<LiveInterval *> ValidIntervals;
+  for (unsigned RegIdx = 0, NumRegs = VRM->getRegInfo().getNumVirtRegs();
+       RegIdx < NumRegs; ++RegIdx) {
+    Register VReg = Register::index2VirtReg(RegIdx);
+    // Only track assigned registers since unassigned ones won't be in Matrix
+    if (VRM->hasPhys(VReg) && LIS->hasInterval(VReg))
+      ValidIntervals.insert(&LIS->getInterval(VReg));
+  }
+
+  // Now scan all LiveIntervalUnions in the matrix and verify each pointer
+  unsigned NumDanglingPointers = 0;
+  for (unsigned I = 0, Size = Matrix.size(); I != Size; ++I) {
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slinder1 wrote:

Nit: inconsistent condition in these two loops, `<` vs `!=`

https://github.com/llvm/llvm-project/pull/168556