[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239740 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/FaultMaps.h

@@ -0,0 +1,73 @@
+//===------------------- FaultMaps.h - StackMaps ----------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_FAULTMAPS_H
+#define LLVM_CODEGEN_FAULTMAPS_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/MC/MCSymbol.h"
+
+#include <vector>
+#include <map>
+
+namespace llvm {
+
+class AsmPrinter;
+class MCExpr;
+class MCSymbol;
+class MCStreamer;
+
+class FaultMaps {
+public:
+  enum FaultType { FaultingLoad = 1, FaultTypeMax };
+
+  static const char *faultTypeToString(FaultType);
+
+  explicit FaultMaps(AsmPrinter &AP);
+
+  void recordFaultingOp(FaultType FaultTy, const MCSymbol *HandlerLabel);
+  void serializeToFaultMapSection();
+
+private:
+  static const char *WFMP;
+
+  struct FaultInfo {
+    FaultType FaultType;
+    const MCExpr *FaultingOffsetExpr;
+    const MCExpr *HandlerOffsetExpr;
+
+    FaultInfo()
+        : FaultType(FaultTypeMax), FaultingOffsetExpr(nullptr),
+          HandlerOffsetExpr(nullptr) {}
+
+    explicit FaultInfo(FaultMaps::FaultType FType, const MCExpr *FaultingOffset,
+                       const MCExpr *HandlerOffset)
+        : FaultType(FType), FaultingOffsetExpr(FaultingOffset),
+          HandlerOffsetExpr(HandlerOffset) {}
+  };
+
+  typedef std::vector<FaultInfo> FunctionFaultInfos;
+
+  // We'd like to keep a stable iteration order for FunctionInfos to help
+  // FileCheck based testing.
+  struct MCSymbolComparator {
+    bool operator()(const MCSymbol *LHS, const MCSymbol *RHS) const {
+      return LHS->getName() < RHS->getName();
+    }
+  };
+
+  std::map<const MCSymbol *, FunctionFaultInfos, MCSymbolComparator>
+      FunctionInfos;
+  AsmPrinter &AP;
+
+  void emitFunctionInfo(const MCSymbol *FnLabel, const FunctionFaultInfos &FFI);
+};
+}
+
+#endif

include/llvm/MC/MCObjectFileInfo.h

@@ -139,6 +139,9 @@ protected:
   /// StackMap section.
   MCSection *StackMapSection;
 
+  /// FaultMap section.
+  MCSection *FaultMapSection;
+
   /// EH frame section.
   ///
   /// It is initialized on demand so it can be overwritten (with uniquing).
@@ -262,6 +265,7 @@ public:
   MCSection *getTLSBSSSection() const { return TLSBSSSection; }
 
   MCSection *getStackMapSection() const { return StackMapSection; }
+  MCSection *getFaultMapSection() const { return FaultMapSection; }
 
   // ELF specific sections.
   MCSection *getDataRelSection() const { return DataRelSection; }

include/llvm/Target/Target.td

@@ -881,6 +881,12 @@ def FRAME_ALLOC : Instruction {
   let hasSideEffects = 0;
   let hasCtrlDep = 1;
 }
+def FAULTING_LOAD_OP : Instruction {
+  let OutOperandList = (outs unknown:$dst);
+  let InOperandList = (ins variable_ops);
+  let usesCustomInserter = 1;
+  let mayLoad = 1;
+}
 }
 
 //===----------------------------------------------------------------------===//

include/llvm/Target/TargetOpcodes.h

@@ -122,6 +122,12 @@ enum {
   /// label. Created by the llvm.frameallocate intrinsic. It has two arguments:
   /// the symbol for the label and the frame index of the stack allocation.
   FRAME_ALLOC = 21,
+
+  /// Loading instruction that may page fault, bundled with associated
+  /// information on how to handle such a page fault.  It is intended to support
+  /// "zero cost" null checks in managed languages by allowing LLVM to fold
+  /// comparisions into existing memory operations.
+  FAULTING_LOAD_OP = 22,
 };
 } // end namespace TargetOpcode
 } // end namespace llvm