1 files changed, 157 insertions, 0 deletions
diff --git a/lib/Transforms/NaCl/ExpandArithWithOverflow.cpp b/lib/Transforms/NaCl/ExpandArithWithOverflow.cpp
new file mode 100644
index 0000000000..e120b24293
--- /dev/null
+++ b/lib/Transforms/NaCl/ExpandArithWithOverflow.cpp
@@ -0,0 +1,157 @@
+//===- ExpandArithWithOverflow.cpp - Expand out uses of *.with.overflow----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// The llvm.*.with.overflow.*() intrinsics are awkward for PNaCl
+// support because they return structs, and we want to omit struct
+// types from IR in PNaCl's stable ABI.
+//
+// However, llvm.{umul,uadd}.with.overflow.*() are used by Clang to
+// implement an overflow check for C++'s new[] operator.  This pass
+// expands out these uses so that PNaCl does not have to support
+// *.with.overflow as part of PNaCl's stable ABI.
+//
+// This pass only handles adding/multiplying by a constant, which is
+// the only use of *.with.overflow that is currently generated by
+// Clang (unless '-ftrapv' is passed to Clang).
+//
+// X * Const overflows iff X > UINT_MAX / Const, where UINT_MAX is the
+// maximum value for the integer type being used.
+//
+// Similarly, X + Const overflows iff X > UINT_MAX - Const.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/NaCl.h"
+
+using namespace llvm;
+
+namespace {
+  // This is a ModulePass so that the pass can easily iterate over all
+  // uses of the intrinsics.
+  class ExpandArithWithOverflow : public ModulePass {
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    ExpandArithWithOverflow() : ModulePass(ID) {
+      initializeExpandArithWithOverflowPass(*PassRegistry::getPassRegistry());
+    }
+
+    virtual bool runOnModule(Module &M);
+  };
+}
+
+char ExpandArithWithOverflow::ID = 0;
+INITIALIZE_PASS(ExpandArithWithOverflow, "expand-arith-with-overflow",
+                "Expand out some uses of *.with.overflow intrinsics",
+                false, false)
+
+static uint64_t UintTypeMax(unsigned Bits) {
+  // Avoid doing 1 << 64 because that is undefined on a uint64_t.
+  if (Bits == 64)
+    return ~(uint64_t) 0;
+  return (((uint64_t) 1) << Bits) - 1;
+}
+
+static bool ExpandOpForIntSize(Module *M, unsigned Bits, bool Mul) {
+  IntegerType *IntTy = IntegerType::get(M->getContext(), Bits);
+  SmallVector<Type *, 1> Types;
+  Types.push_back(IntTy);
+  Intrinsic::ID ID = (Mul ? Intrinsic::umul_with_overflow
+                          : Intrinsic::uadd_with_overflow);
+  std::string Name = Intrinsic::getName(ID, Types);
+  Function *Intrinsic = M->getFunction(Name);
+  if (!Intrinsic)
+    return false;
+  for (Value::use_iterator CallIter = Intrinsic->use_begin(),
+         E = Intrinsic->use_end(); CallIter != E; ) {
+    CallInst *Call = dyn_cast<CallInst>(*CallIter++);
+    if (!Call) {
+      report_fatal_error("ExpandArithWithOverflow: Taking the address of a "
+                         "*.with.overflow intrinsic is not allowed");
+    }
+    Value *VariableArg;
+    ConstantInt *ConstantArg;
+    if (ConstantInt *C = dyn_cast<ConstantInt>(Call->getArgOperand(0))) {
+      VariableArg = Call->getArgOperand(1);
+      ConstantArg = C;
+    } else if (ConstantInt *C = dyn_cast<ConstantInt>(Call->getArgOperand(1))) {
+      VariableArg = Call->getArgOperand(0);
+      ConstantArg = C;
+    } else {
+      errs() << "Use: " << *Call << "\n";
+      report_fatal_error("ExpandArithWithOverflow: At least one argument of "
+                         "*.with.overflow must be a constant");
+    }
+
+    Value *ArithResult = BinaryOperator::Create(
+        (Mul ? Instruction::Mul : Instruction::Add), VariableArg, ConstantArg,
+        Call->getName() + ".arith", Call);
+
+    uint64_t ArgMax;
+    if (Mul) {
+      ArgMax = UintTypeMax(Bits) / ConstantArg->getZExtValue();
+    } else {
+      ArgMax = UintTypeMax(Bits) - ConstantArg->getZExtValue();
+    }
+    Value *Overflow = new ICmpInst(
+        Call, CmpInst::ICMP_UGT, VariableArg, ConstantInt::get(IntTy, ArgMax),
+        Call->getName() + ".overflow");
+
+    for (Value::use_iterator FieldIter = Call->use_begin(),
+           E = Call->use_end(); FieldIter != E; ) {
+      User *U = *FieldIter++;
+      ExtractValueInst *Field = dyn_cast<ExtractValueInst>(U);
+      if (!Field) {
+        errs() << "Use: " << *U << "\n";
+        report_fatal_error(
+            "ExpandArithWithOverflow: Use is not an extractvalue");
+      }
+      if (Field->getNumIndices() != 1) {
+        report_fatal_error("ExpandArithWithOverflow: Unexpected indices");
+      }
+      unsigned Index = Field->getIndices()[0];
+      if (Index == 0) {
+        Field->replaceAllUsesWith(ArithResult);
+      } else if (Index == 1) {
+        Field->replaceAllUsesWith(Overflow);
+      } else {
+        report_fatal_error("ExpandArithWithOverflow: Unexpected index");
+      }
+      Field->eraseFromParent();
+    }
+    Call->eraseFromParent();
+  }
+  Intrinsic->eraseFromParent();
+  return true;
+}
+
+static bool ExpandForIntSize(Module *M, unsigned Bits) {
+  bool Modified = false;
+  Modified |= ExpandOpForIntSize(M, Bits, true); // Expand umul
+  Modified |= ExpandOpForIntSize(M, Bits, false); // Expand uadd
+  return Modified;
+}
+
+bool ExpandArithWithOverflow::runOnModule(Module &M) {
+  bool Modified = false;
+  Modified |= ExpandForIntSize(&M, 64);
+  Modified |= ExpandForIntSize(&M, 32);
+  Modified |= ExpandForIntSize(&M, 16);
+  Modified |= ExpandForIntSize(&M, 8);
+  return Modified;
+}
+
+ModulePass *llvm::createExpandArithWithOverflowPass() {
+  return new ExpandArithWithOverflow();
+}