[MachineVerifier] Improve verification of live-in lists.

MachineVerifier::visitMachineFunctionAfter() is extended to check the
live-through case for live-in lists. This is only done for registers without
aliases and that are neither allocatable or reserved, such as the SystemZ::CC
register.

The MachineVerifier earlier only catched the case of a live-in use without
an entry in the live-in list (as "using an undefined physical register").

A comment in LivePhysRegs.h has been added stating a guarantee that
addLiveOuts() can be trusted for a full register both before and after
register allocation.

Review: Quentin Colombet
https://reviews.llvm.org/D68267

1 files changed, 26 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineVerifier.cpp b/llvm/lib/CodeGen/MachineVerifier.cpp
index 969743e..b5dea28 100644
--- a/llvm/lib/CodeGen/MachineVerifier.cpp
+++ b/llvm/lib/CodeGen/MachineVerifier.cpp
@@ -2304,6 +2304,32 @@ void MachineVerifier::visitMachineFunctionAfter() {
   if (LiveInts)
     verifyLiveIntervals();
 
+  // Check live-in list of each MBB. If a register is live into MBB, check
+  // that the register is in regsLiveOut of each predecessor block. Since
+  // this must come from a definition in the predecesssor or its live-in
+  // list, this will catch a live-through case where the predecessor does not
+  // have the register in its live-in list.  This currently only checks
+  // registers that have no aliases, are not allocatable and are not
+  // reserved, which could mean a condition code register for instance.
+  if (MRI->tracksLiveness())
+    for (const auto &MBB : *MF)
+      for (MachineBasicBlock::RegisterMaskPair P : MBB.liveins()) {
+        MCPhysReg LiveInReg = P.PhysReg;
+        bool hasAliases = MCRegAliasIterator(LiveInReg, TRI, false).isValid();
+        if (hasAliases || isAllocatable(LiveInReg) || isReserved(LiveInReg))
+          continue;
+        for (const MachineBasicBlock *Pred : MBB.predecessors()) {
+          BBInfo &PInfo = MBBInfoMap[Pred];
+          if (!PInfo.regsLiveOut.count(LiveInReg)) {
+            report("Live in register not found to be live out from predecessor.",
+                   &MBB);
+            errs() << TRI->getName(LiveInReg)
+                   << " not found to be live out from "
+                   << printMBBReference(*Pred) << "\n";
+          }
+        }
+      }
+
   for (auto CSInfo : MF->getCallSitesInfo())
     if (!CSInfo.first->isCall())
       report("Call site info referencing instruction that is not call", MF);