[X86] Re-enable conditional tail calls and fix PR31257.

This reverts r294348, which removed support for conditional tail calls
due to the PR above. It fixes the PR by marking live registers as
implicitly used and defined by the now predicated tailcall. This is
similar to how IfConversion predicates instructions.

Differential Revision: https://reviews.llvm.org/D29856

llvm-svn: 295262

1 files changed, 8 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index 0887643ed5a..65949531126 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -499,11 +499,16 @@ ReSimplify:
     break;
   }
 
-  // TAILJMPd, TAILJMPd64 - Lower to the correct jump instruction.
+  // TAILJMPd, TAILJMPd64, TailJMPd_cc - Lower to the correct jump instruction.
   { unsigned Opcode;
   case X86::TAILJMPr:   Opcode = X86::JMP32r; goto SetTailJmpOpcode;
   case X86::TAILJMPd:
   case X86::TAILJMPd64: Opcode = X86::JMP_1;  goto SetTailJmpOpcode;
+  case X86::TAILJMPd_CC:
+  case X86::TAILJMPd64_CC:
+    Opcode = X86::GetCondBranchFromCond(
+        static_cast<X86::CondCode>(MI->getOperand(1).getImm()));
+    goto SetTailJmpOpcode;
 
   SetTailJmpOpcode:
     MCOperand Saved = OutMI.getOperand(0);
@@ -1294,9 +1299,11 @@ void X86AsmPrinter::EmitInstruction(const MachineInstr *MI) {
   case X86::TAILJMPr:
   case X86::TAILJMPm:
   case X86::TAILJMPd:
+  case X86::TAILJMPd_CC:
   case X86::TAILJMPr64:
   case X86::TAILJMPm64:
   case X86::TAILJMPd64:
+  case X86::TAILJMPd64_CC:
   case X86::TAILJMPr64_REX:
   case X86::TAILJMPm64_REX:
     // Lower these as normal, but add some comments.