[LiveVariables] Don't set undef reg PHI used as live for FromMBB

Summary:
In the patch D73152, it adds a new function LiveVariables::addNewBlock.
This new function will add the reg which PHI used to the MBB which reg
is from.
But the new function may cause LiveVariable Verification failed when the
Src reg in PHI is undef.

Reviewed By: bjope

Differential Revision: https://reviews.llvm.org/D80077

diff --git a/llvm/lib/CodeGen/LiveVariables.cpp b/llvm/lib/CodeGen/LiveVariables.cpp
index 7e89471..6610491 100644 (file)
--- a/llvm/lib/CodeGen/LiveVariables.cpp
+++ b/llvm/lib/CodeGen/LiveVariables.cpp
@@ -828,7 +828,8 @@ void LiveVariables::addNewBlock(MachineBasicBlock *BB,
          BBE = SuccBB->end();
        BBI != BBE && BBI->isPHI(); ++BBI) {
     for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2)
-      if (BBI->getOperand(i + 1).getMBB() == BB)
+      if (BBI->getOperand(i + 1).getMBB() == BB &&
+          BBI->getOperand(i).readsReg())
         getVarInfo(BBI->getOperand(i).getReg())
           .AliveBlocks.set(NumNew);
   }

diff --git a/llvm/test/CodeGen/AArch64/PHIElimination-crash.mir b/llvm/test/CodeGen/AArch64/PHIElimination-crash.mir
new file mode 100644 (file)
index 0000000..1a1ba15
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/PHIElimination-crash.mir
@@ -0,0 +1,25 @@
+# RUN: llc -mtriple=aarch64-linux-gnu -verify-machineinstrs -o /dev/null %s \
+# RUN:   -run-pass=livevars,phi-node-elimination,twoaddressinstruction \
+# RUN:   -no-phi-elim-live-out-early-exit=1 -phi-elim-split-all-critical-edges=1
+
+# Used to result in
+#
+#     *** Bad machine code: LiveVariables: Block should not be in AliveBlocks ***
+#
+# Just verify that we do not crash (or get verifier error).
+
+---
+name: test
+tracksRegLiveness: true
+body: |
+  bb.0:
+    liveins: $nzcv, $wzr
+    Bcc 8, %bb.2, implicit $nzcv
+
+  bb.1:
+    %x:gpr32 = COPY $wzr
+
+  bb.2:
+    %y:gpr32 = PHI %x:gpr32, %bb.1, undef %undef:gpr32, %bb.0
+    $wzr = COPY %y:gpr32
+...