[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

1 files changed, 114 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/FaultMaps.cpp b/llvm/lib/CodeGen/FaultMaps.cpp
new file mode 100644
index 00000000000..2f849511d69
--- /dev/null
+++ b/llvm/lib/CodeGen/FaultMaps.cpp
@@ -0,0 +1,114 @@
+//===---------------------------- FaultMaps.cpp ---------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/FaultMaps.h"
+
+#include "llvm/CodeGen/AsmPrinter.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCObjectFileInfo.h"
+#include "llvm/MC/MCStreamer.h"
+#include "llvm/Support/Debug.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "faultmaps"
+
+static const int FaultMapVersion = 1;
+const char *FaultMaps::WFMP = "Fault Maps: ";
+
+FaultMaps::FaultMaps(AsmPrinter &AP) : AP(AP) {}
+
+void FaultMaps::recordFaultingOp(FaultType FaultTy,
+                                 const MCSymbol *HandlerLabel) {
+  MCContext &OutContext = AP.OutStreamer->getContext();
+  MCSymbol *FaultingLabel = OutContext.createTempSymbol();
+
+  AP.OutStreamer->EmitLabel(FaultingLabel);
+
+  const MCExpr *FaultingOffset = MCBinaryExpr::createSub(
+      MCSymbolRefExpr::create(FaultingLabel, OutContext),
+      MCSymbolRefExpr::create(AP.CurrentFnSymForSize, OutContext), OutContext);
+
+  const MCExpr *HandlerOffset = MCBinaryExpr::createSub(
+      MCSymbolRefExpr::create(HandlerLabel, OutContext),
+      MCSymbolRefExpr::create(AP.CurrentFnSymForSize, OutContext), OutContext);
+
+  FunctionInfos[AP.CurrentFnSym].emplace_back(FaultTy, FaultingOffset,
+                                              HandlerOffset);
+}
+
+void FaultMaps::serializeToFaultMapSection() {
+  if (FunctionInfos.empty())
+    return;
+
+  MCContext &OutContext = AP.OutStreamer->getContext();
+  MCStreamer &OS = *AP.OutStreamer;
+
+  // Create the section.
+  MCSection *FaultMapSection =
+      OutContext.getObjectFileInfo()->getFaultMapSection();
+  OS.SwitchSection(FaultMapSection);
+
+  // Emit a dummy symbol to force section inclusion.
+  OS.EmitLabel(OutContext.getOrCreateSymbol(Twine("__LLVM_FaultMaps")));
+
+  DEBUG(dbgs() << "********** Fault Map Output **********\n");
+
+  // Header
+  OS.EmitIntValue(FaultMapVersion, 1); // Version.
+  OS.EmitIntValue(0, 1);               // Reserved.
+  OS.EmitIntValue(0, 2);               // Reserved.
+
+  DEBUG(dbgs() << WFMP << "#functions = " << FunctionInfos.size() << "\n");
+  OS.EmitIntValue(FunctionInfos.size(), 4);
+
+  DEBUG(dbgs() << WFMP << "functions:\n");
+
+  for (const auto &FFI : FunctionInfos)
+    emitFunctionInfo(FFI.first, FFI.second);
+}
+
+void FaultMaps::emitFunctionInfo(const MCSymbol *FnLabel,
+                                 const FunctionFaultInfos &FFI) {
+  MCStreamer &OS = *AP.OutStreamer;
+
+  DEBUG(dbgs() << WFMP << "  function addr: " << *FnLabel << "\n");
+  OS.EmitSymbolValue(FnLabel, 8);
+
+  DEBUG(dbgs() << WFMP << "  #faulting PCs: " << FFI.size() << "\n");
+  OS.EmitIntValue(FFI.size(), 4);
+
+  OS.EmitIntValue(0, 4); // Reserved
+
+  for (auto &Fault : FFI) {
+    DEBUG(dbgs() << WFMP << "    fault type: "
+          << faultTypeToString(Fault.FaultType) << "\n");
+    OS.EmitIntValue(Fault.FaultType, 4);
+
+    DEBUG(dbgs() << WFMP << "    faulting PC offset: "
+          << *Fault.FaultingOffsetExpr << "\n");
+    OS.EmitValue(Fault.FaultingOffsetExpr, 4);
+
+    DEBUG(dbgs() << WFMP << "    fault handler PC offset: "
+          << *Fault.HandlerOffsetExpr << "\n");
+    OS.EmitValue(Fault.HandlerOffsetExpr, 4);
+  }
+}
+
+
+const char *FaultMaps::faultTypeToString(FaultMaps::FaultType FT) {
+  switch (FT) {
+  default:
+    llvm_unreachable("unhandled fault type!");
+
+  case FaultMaps::FaultingLoad:
+    return "FaultingLoad";
+  }
+}