[PATCH] D80077: [LiveVariables] Don't set undef reg PHI used as live for FromMBB

[Zhang Kang via Phabricator via llvm-commits]

ZhangKang updated this revision to Diff 265110.
ZhangKang added a comment.

Use a small test case.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D80077/new/

https://reviews.llvm.org/D80077

Files:
  llvm/lib/CodeGen/LiveVariables.cpp
  llvm/test/CodeGen/AArch64/PHIElimination-crash.mir


Index: llvm/test/CodeGen/AArch64/PHIElimination-crash.mir
===================================================================
--- /dev/null
+++ 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
+...
Index: llvm/lib/CodeGen/LiveVariables.cpp
===================================================================
--- llvm/lib/CodeGen/LiveVariables.cpp
+++ llvm/lib/CodeGen/LiveVariables.cpp
@@ -828,7 +828,8 @@
          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);
   }


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