[Statepoints] Support for "patchable" statepoints.

Summary:
This change adds two new parameters to the statepoint intrinsic, `i64 id`
and `i32 num_patch_bytes`.  `id` gets propagated to the ID field
in the generated StackMap section.  If the `num_patch_bytes` is
non-zero then the statepoint is lowered to `num_patch_bytes` bytes of
nops instead of a call (the spill and reload code remains unchanged).
A non-zero `num_patch_bytes` is useful in situations where a language
runtime requires complete control over how a call is lowered.

This change brings statepoints one step closer to patchpoints.  With
some additional work (that is not part of this patch) it should be
possible to get rid of `TargetOpcode::STATEPOINT` altogether.

PlaceSafepoints generates `statepoint` wrappers with `id` set to
`0xABCDEF00` (the old default value for the ID reported in the stackmap)
and `num_patch_bytes` set to `0`.  This can be made more sophisticated
later.

Reviewers: reames, pgavlin, swaroop.sridhar, AndyAyers

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9546

llvm-svn: 237214

1 files changed, 43 insertions, 36 deletions

diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index 273444cccc0..d55e9f656b0 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -812,43 +812,50 @@ void X86AsmPrinter::LowerSTATEPOINT(const MachineInstr &MI,
                                     X86MCInstLower &MCIL) {
   assert(Subtarget->is64Bit() && "Statepoint currently only supports X86-64");
 
-  // Lower call target and choose correct opcode
-  const MachineOperand &CallTarget = StatepointOpers(&MI).getCallTarget();
-  MCOperand CallTargetMCOp;
-  unsigned CallOpcode;
-  switch (CallTarget.getType()) {
-  case MachineOperand::MO_GlobalAddress:
-  case MachineOperand::MO_ExternalSymbol:
-    CallTargetMCOp = MCIL.LowerSymbolOperand(
-        CallTarget, MCIL.GetSymbolFromOperand(CallTarget));
-    CallOpcode = X86::CALL64pcrel32;
-    // Currently, we only support relative addressing with statepoints.
-    // Otherwise, we'll need a scratch register to hold the target
-    // address.  You'll fail asserts during load & relocation if this
-    // symbol is to far away. (TODO: support non-relative addressing)
-    break;
-  case MachineOperand::MO_Immediate:
-    CallTargetMCOp = MCOperand::CreateImm(CallTarget.getImm());
-    CallOpcode = X86::CALL64pcrel32;
-    // Currently, we only support relative addressing with statepoints.
-    // Otherwise, we'll need a scratch register to hold the target
-    // immediate.  You'll fail asserts during load & relocation if this
-    // address is to far away. (TODO: support non-relative addressing)
-    break;
-  case MachineOperand::MO_Register:
-    CallTargetMCOp = MCOperand::CreateReg(CallTarget.getReg());
-    CallOpcode = X86::CALL64r;
-    break;
-  default:
-    llvm_unreachable("Unsupported operand type in statepoint call target");
-    break;
-  }
+  StatepointOpers SOpers(&MI);
 
-  // Emit call
-  MCInst CallInst;
-  CallInst.setOpcode(CallOpcode);
-  CallInst.addOperand(CallTargetMCOp);
-  OutStreamer->EmitInstruction(CallInst, getSubtargetInfo());
+  if (unsigned PatchBytes = SOpers.getNumPatchBytes()) {
+    EmitNops(*OutStreamer, PatchBytes, Subtarget->is64Bit(),
+             getSubtargetInfo());
+  } else {
+    // Lower call target and choose correct opcode
+    const MachineOperand &CallTarget = SOpers.getCallTarget();
+    MCOperand CallTargetMCOp;
+    unsigned CallOpcode;
+    switch (CallTarget.getType()) {
+    case MachineOperand::MO_GlobalAddress:
+    case MachineOperand::MO_ExternalSymbol:
+      CallTargetMCOp = MCIL.LowerSymbolOperand(
+          CallTarget, MCIL.GetSymbolFromOperand(CallTarget));
+      CallOpcode = X86::CALL64pcrel32;
+      // Currently, we only support relative addressing with statepoints.
+      // Otherwise, we'll need a scratch register to hold the target
+      // address.  You'll fail asserts during load & relocation if this
+      // symbol is to far away. (TODO: support non-relative addressing)
+      break;
+    case MachineOperand::MO_Immediate:
+      CallTargetMCOp = MCOperand::CreateImm(CallTarget.getImm());
+      CallOpcode = X86::CALL64pcrel32;
+      // Currently, we only support relative addressing with statepoints.
+      // Otherwise, we'll need a scratch register to hold the target
+      // immediate.  You'll fail asserts during load & relocation if this
+      // address is to far away. (TODO: support non-relative addressing)
+      break;
+    case MachineOperand::MO_Register:
+      CallTargetMCOp = MCOperand::CreateReg(CallTarget.getReg());
+      CallOpcode = X86::CALL64r;
+      break;
+    default:
+      llvm_unreachable("Unsupported operand type in statepoint call target");
+      break;
+    }
+
+    // Emit call
+    MCInst CallInst;
+    CallInst.setOpcode(CallOpcode);
+    CallInst.addOperand(CallTargetMCOp);
+    OutStreamer->EmitInstruction(CallInst, getSubtargetInfo());
+  }
 
   // Record our statepoint node in the same section used by STACKMAP
   // and PATCHPOINT