commit c63244daa19971760aed20a40d938ff592ad3574
author Sanjoy Das <sanjoy@playingwithpointers.com> Mon Jun 15 18:44:08 2015 +0000
committer Sanjoy Das <sanjoy@playingwithpointers.com> Mon Jun 15 18:44:08 2015 +0000
tree de4416d659f970f83bb3a4c8330bac7a7932b9c8
parent 2d869b230b482c6a7972d8cd4948ef2b96e389d8

[CodeGen] Introduce a FAULTING_LOAD_OP pseudo-op.

Summary:
This instruction encodes a loading operation that may fault, and a label
to branch to if the load page-faults.  The locations of potentially
faulting loads and their "handler" destinations are recorded in a
FaultMap section, meant to be consumed by LLVM's clients.

Nothing generates FAULTING_LOAD_OP instructions yet, but they will be
used in a future change.

The documentation (FaultMaps.rst) needs improvement and I will update
this diff with a more expanded version shortly.

Depends on D10196

Reviewers: rnk, reames, AndyAyers, ab, atrick, pgavlin

Reviewed By: atrick, pgavlin

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D10197

llvm-svn: 239740

llvm/lib/Target/X86/X86AsmPrinter.cpp

diff --git a/llvm/lib/Target/X86/X86AsmPrinter.cpp b/llvm/lib/Target/X86/X86AsmPrinter.cpp
index 64fc6d0..3b11e69 100644
--- a/llvm/lib/Target/X86/X86AsmPrinter.cpp
+++ b/llvm/lib/Target/X86/X86AsmPrinter.cpp
@@ -674,6 +674,7 @@
     }
 
     SM.serializeToStackMapSection();
+    FM.serializeToFaultMapSection();
 
     // Funny Darwin hack: This flag tells the linker that no global symbols
     // contain code that falls through to other global symbols (e.g. the obvious
@@ -726,8 +727,10 @@
     }
   }
 
-  if (TT.isOSBinFormatELF())
+  if (TT.isOSBinFormatELF()) {
     SM.serializeToStackMapSection();
+    FM.serializeToFaultMapSection();
+  }
 }
 
 //===----------------------------------------------------------------------===//

llvm/lib/Target/X86/X86AsmPrinter.h

diff --git a/llvm/lib/Target/X86/X86AsmPrinter.h b/llvm/lib/Target/X86/X86AsmPrinter.h
index 3beeb17..acba211 100644
--- a/llvm/lib/Target/X86/X86AsmPrinter.h
+++ b/llvm/lib/Target/X86/X86AsmPrinter.h
@@ -12,6 +12,7 @@
 
 #include "X86Subtarget.h"
 #include "llvm/CodeGen/AsmPrinter.h"
+#include "llvm/CodeGen/FaultMaps.h"
 #include "llvm/CodeGen/StackMaps.h"
 #include "llvm/Target/TargetMachine.h"
 
@@ -27,6 +28,7 @@
 class LLVM_LIBRARY_VISIBILITY X86AsmPrinter : public AsmPrinter {
   const X86Subtarget *Subtarget;
   StackMaps SM;
+  FaultMaps FM;
 
   void GenerateExportDirective(const MCSymbol *Sym, bool IsData);
 
@@ -83,13 +85,15 @@
   void LowerSTACKMAP(const MachineInstr &MI);
   void LowerPATCHPOINT(const MachineInstr &MI, X86MCInstLower &MCIL);
   void LowerSTATEPOINT(const MachineInstr &MI, X86MCInstLower &MCIL);
+  void LowerFAULTING_LOAD_OP(const MachineInstr &MI, X86MCInstLower &MCIL);
 
   void LowerTlsAddr(X86MCInstLower &MCInstLowering, const MachineInstr &MI);
 
  public:
    explicit X86AsmPrinter(TargetMachine &TM,
                           std::unique_ptr<MCStreamer> Streamer)
-       : AsmPrinter(TM, std::move(Streamer)), SM(*this), SMShadowTracker(TM) {}
+       : AsmPrinter(TM, std::move(Streamer)), SM(*this), FM(*this),
+         SMShadowTracker(TM) {}
 
   const char *getPassName() const override {
     return "X86 Assembly / Object Emitter";

llvm/lib/Target/X86/X86MCInstLower.cpp

diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index e47ab17..655e06a 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -864,6 +864,28 @@
   SM.recordStatepoint(MI);
 }
 
+void X86AsmPrinter::LowerFAULTING_LOAD_OP(const MachineInstr &MI,
+                                       X86MCInstLower &MCIL) {
+  // FAULTING_LOAD_OP <def>, <handler label>, <load opcode>, <load operands>
+
+  unsigned LoadDefRegister = MI.getOperand(0).getReg();
+  MCSymbol *HandlerLabel = MI.getOperand(1).getMCSymbol();
+  unsigned LoadOpcode = MI.getOperand(2).getImm();
+  unsigned LoadOperandsBeginIdx = 3;
+
+  FM.recordFaultingOp(FaultMaps::FaultingLoad, HandlerLabel);
+
+  MCInst LoadMI;
+  LoadMI.setOpcode(LoadOpcode);
+  LoadMI.addOperand(MCOperand::createReg(LoadDefRegister));
+  for (auto I = MI.operands_begin() + LoadOperandsBeginIdx,
+            E = MI.operands_end();
+       I != E; ++I)
+    if (auto MaybeOperand = MCIL.LowerMachineOperand(&MI, *I))
+      LoadMI.addOperand(MaybeOperand.getValue());
+
+  OutStreamer->EmitInstruction(LoadMI, getSubtargetInfo());
+}
 
 // Lower a stackmap of the form:
 // <id>, <shadowBytes>, ...
@@ -1119,6 +1141,9 @@
   case TargetOpcode::STATEPOINT:
     return LowerSTATEPOINT(*MI, MCInstLowering);
 
+  case TargetOpcode::FAULTING_LOAD_OP:
+    return LowerFAULTING_LOAD_OP(*MI, MCInstLowering);
+
   case TargetOpcode::STACKMAP:
     return LowerSTACKMAP(*MI);