MC: mayAffectControlFlow() handling for variadic instructions.

Variadic MC instructions don't note whether the variable operands
are uses or defs, so mayAffectControlFlow() must conservatively
assume they are defs and return true if the PC is in the operand
list.

rdar://14488628

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186846 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 14 insertions, 2 deletions

diff --git a/include/llvm/MC/MCInstrDesc.h b/include/llvm/MC/MCInstrDesc.h
index 9b5415add2..310f706877 100644
--- a/include/llvm/MC/MCInstrDesc.h
+++ b/include/llvm/MC/MCInstrDesc.h
@@ -268,8 +268,20 @@ public:
     if (isBranch() || isCall() || isReturn() || isIndirectBranch())
       return true;
     unsigned PC = RI.getProgramCounter();
-    if (PC == 0) return false;
-    return hasDefOfPhysReg(MI, PC, RI);
+    if (PC == 0)
+      return false;
+    if (hasDefOfPhysReg(MI, PC, RI))
+      return true;
+    // A variadic instruction may define PC in the variable operand list.
+    // There's currently no indication of which entries in a variable
+    // list are defs and which are uses. While that's the case, this function
+    // needs to assume they're defs in order to be conservatively correct.
+    for (int i = NumOperands, e = MI.getNumOperands(); i != e; ++i) {
+      if (MI.getOperand(i).isReg() &&
+          RI.isSubRegisterEq(PC, MI.getOperand(i).getReg()))
+        return true;
+    }
+    return false;
   }
 
   /// \brief Return true if this instruction has a predicate operand