Tail duplication can mix incompatible registers in phi nodes

Do not tail duplicate blocks where the successor has a phi node,
and the corresponding value in that phi node uses a subregister.

http://reviews.llvm.org/D13922

llvm-svn: 250877

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/TailDuplication.cpp b/llvm/lib/CodeGen/TailDuplication.cpp
index c2e8b93..ff86dab 100644
--- a/llvm/lib/CodeGen/TailDuplication.cpp
+++ b/llvm/lib/CodeGen/TailDuplication.cpp
@@ -607,6 +607,27 @@ TailDuplicatePass::shouldTailDuplicate(const MachineFunction &MF,
       return false;
   }
 
+  // Check if any of the successors of TailBB has a PHI node in which the
+  // value corresponding to TailBB uses a subregister.
+  // If a phi node uses a register paired with a subregister, the actual
+  // "value type" of the phi may differ from the type of the register without
+  // any subregisters. Due to a bug, tail duplication may add a new operand
+  // without a necessary subregister, producing an invalid code. This is
+  // demonstrated by test/CodeGen/Hexagon/tail-dup-subreg-abort.ll.
+  // Disable tail duplication for this case for now, until the problem is
+  // fixed.
+  for (auto SB : TailBB.successors()) {
+    for (auto &I : *SB) {
+      if (!I.isPHI())
+        break;
+      unsigned Idx = getPHISrcRegOpIdx(&I, &TailBB);
+      assert(Idx != 0);
+      MachineOperand &PU = I.getOperand(Idx);
+      if (PU.getSubReg() != 0)
+        return false;
+    }
+  }
+
   if (HasIndirectbr && PreRegAlloc)
     return true;