PNaCl: Add ExpandSmallArguments pass to widen parameters to 32 bits

This widens i1, i8 and i16 function arguments and return types.

Factor out RecreateFunction() helper function from existing PNaCl
passes since this is a reoccurring code fragment.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3342
TEST=*.ll tests + PNaCl toolchain trybots + GCC torture tests + LLVM test suite

Review URL: https://codereview.chromium.org/15971007

1 files changed, 217 insertions, 0 deletions

diff --git a/lib/Transforms/NaCl/ExpandSmallArguments.cpp b/lib/Transforms/NaCl/ExpandSmallArguments.cpp
new file mode 100644
index 0000000000..c8a321edb9
--- /dev/null
+++ b/lib/Transforms/NaCl/ExpandSmallArguments.cpp
@@ -0,0 +1,217 @@
+//===- ExpandSmallArguments.cpp - Expand out arguments smaller than i32----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// LLVM IR allows function return types and argument types such as
+// "zeroext i8" and "signext i8".  The Language Reference says that
+// zeroext "indicates to the code generator that the parameter or
+// return value should be zero-extended to the extent required by the
+// target's ABI (which is usually 32-bits, but is 8-bits for a i1 on
+// x86-64) by the caller (for a parameter) or the callee (for a return
+// value)".
+//
+// This can lead to non-portable behaviour when calling functions
+// without C prototypes or with wrong C prototypes.
+//
+// In order to remove this non-portability from PNaCl, and to simplify
+// the language that the PNaCl translator accepts, the
+// ExpandSmallArguments pass widens integer arguments and return types
+// to be at least 32 bits.  The pass inserts explicit cast
+// instructions (ZExtInst/SExtInst/TruncInst) as needed.
+//
+// The pass chooses between ZExtInst and SExtInst widening based on
+// whether a "signext" attribute is present.  However, in principle
+// the pass could always use zero-extension, because the extent to
+// which either zero-extension or sign-extension is done is up to the
+// target ABI, which is up to PNaCl to specify.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/NaCl.h"
+
+using namespace llvm;
+
+namespace {
+  // This is a ModulePass because the pass recreates functions in
+  // order to change their arguments' types.
+  class ExpandSmallArguments : public ModulePass {
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    ExpandSmallArguments() : ModulePass(ID) {
+      initializeExpandSmallArgumentsPass(*PassRegistry::getPassRegistry());
+    }
+
+    virtual bool runOnModule(Module &M);
+  };
+}
+
+char ExpandSmallArguments::ID = 0;
+INITIALIZE_PASS(ExpandSmallArguments, "expand-small-arguments",
+                "Expand function arguments to be at least 32 bits in size",
+                false, false)
+
+// Returns the normalized version of the given argument/return type.
+static Type *NormalizeType(Type *Ty) {
+  if (IntegerType *IntTy = dyn_cast<IntegerType>(Ty)) {
+    if (IntTy->getBitWidth() < 32) {
+      return IntegerType::get(Ty->getContext(), 32);
+    }
+  }
+  return Ty;
+}
+
+// Returns the normalized version of the given function type.
+static FunctionType *NormalizeFunctionType(FunctionType *FTy) {
+  if (FTy->isVarArg()) {
+    report_fatal_error(
+        "ExpandSmallArguments does not handle varargs functions");
+  }
+  SmallVector<Type *, 8> ArgTypes;
+  for (unsigned I = 0; I < FTy->getNumParams(); ++I) {
+    ArgTypes.push_back(NormalizeType(FTy->getParamType(I)));
+  }
+  return FunctionType::get(NormalizeType(FTy->getReturnType()),
+                           ArgTypes, false);
+}
+
+// Convert the given function to use normalized argument/return types.
+static bool ConvertFunction(Function *Func) {
+  FunctionType *FTy = Func->getFunctionType();
+  FunctionType *NFTy = NormalizeFunctionType(FTy);
+  if (NFTy == FTy)
+    return false; // No change needed.
+  Function *NewFunc = RecreateFunction(Func, NFTy);
+
+  // Move the arguments across to the new function.
+  for (Function::arg_iterator Arg = Func->arg_begin(), E = Func->arg_end(),
+         NewArg = NewFunc->arg_begin();
+       Arg != E; ++Arg, ++NewArg) {
+    NewArg->takeName(Arg);
+    if (Arg->getType() == NewArg->getType()) {
+      Arg->replaceAllUsesWith(NewArg);
+    } else {
+      Instruction *Trunc = new TruncInst(
+          NewArg, Arg->getType(), NewArg->getName() + ".arg_trunc",
+          NewFunc->getEntryBlock().getFirstInsertionPt());
+      Arg->replaceAllUsesWith(Trunc);
+    }
+  }
+
+  if (FTy->getReturnType() != NFTy->getReturnType()) {
+    // Fix up return instructions.
+    Instruction::CastOps CastType =
+        Func->getAttributes().hasAttribute(0, Attribute::SExt) ?
+        Instruction::SExt : Instruction::ZExt;
+    for (Function::iterator BB = NewFunc->begin(), E = NewFunc->end();
+         BB != E;
+         ++BB) {
+      for (BasicBlock::iterator Iter = BB->begin(), E = BB->end();
+           Iter != E; ) {
+        Instruction *Inst = Iter++;
+        if (ReturnInst *Ret = dyn_cast<ReturnInst>(Inst)) {
+          Value *Ext = CopyDebug(
+              CastInst::Create(CastType, Ret->getReturnValue(),
+                               NFTy->getReturnType(),
+                               Ret->getReturnValue()->getName() + ".ret_ext",
+                               Ret),
+              Ret);
+          CopyDebug(ReturnInst::Create(Ret->getContext(), Ext, Ret), Ret);
+          Ret->eraseFromParent();
+        }
+      }
+    }
+  }
+
+  Func->eraseFromParent();
+  return true;
+}
+
+// Convert the given call to use normalized argument/return types.
+static bool ConvertCall(CallInst *Call) {
+  // Don't try to change calls to intrinsics.
+  if (isa<IntrinsicInst>(Call))
+    return false;
+  FunctionType *FTy = cast<FunctionType>(
+      Call->getCalledValue()->getType()->getPointerElementType());
+  FunctionType *NFTy = NormalizeFunctionType(FTy);
+  if (NFTy == FTy)
+    return false; // No change needed.
+
+  // Convert arguments.
+  SmallVector<Value *, 8> Args;
+  for (unsigned I = 0; I < Call->getNumArgOperands(); ++I) {
+    Value *Arg = Call->getArgOperand(I);
+    if (NFTy->getParamType(I) != FTy->getParamType(I)) {
+      Instruction::CastOps CastType =
+          Call->getAttributes().hasAttribute(I + 1, Attribute::SExt) ?
+          Instruction::SExt : Instruction::ZExt;
+      Arg = CopyDebug(CastInst::Create(CastType, Arg, NFTy->getParamType(I),
+                                       "arg_ext", Call), Call);
+    }
+    Args.push_back(Arg);
+  }
+  Value *CastFunc =
+    CopyDebug(new BitCastInst(Call->getCalledValue(), NFTy->getPointerTo(),
+                              Call->getName() + ".arg_cast", Call), Call);
+  CallInst *NewCall = CallInst::Create(CastFunc, Args, "", Call);
+  CopyDebug(NewCall, Call);
+  NewCall->takeName(Call);
+  NewCall->setAttributes(Call->getAttributes());
+  NewCall->setCallingConv(Call->getCallingConv());
+  NewCall->setTailCall(Call->isTailCall());
+  Value *Result = NewCall;
+  if (FTy->getReturnType() != NFTy->getReturnType()) {
+    Result = CopyDebug(new TruncInst(NewCall, FTy->getReturnType(),
+                                     NewCall->getName() + ".ret_trunc",
+                                     Call), Call);
+  }
+  Call->replaceAllUsesWith(Result);
+  Call->eraseFromParent();
+  return true;
+}
+
+bool ExpandSmallArguments::runOnModule(Module &M) {
+  bool Changed = false;
+  for (Module::iterator Iter = M.begin(), E = M.end(); Iter != E; ) {
+    Function *Func = Iter++;
+    // Don't try to change intrinsic declarations because intrinsics
+    // will continue to have non-normalized argument types.  For
+    // example, memset() takes an i8 argument.  It shouldn't matter
+    // whether we modify the types of other function declarations, but
+    // we don't expect to see non-intrinsic function declarations in a
+    // PNaCl pexe.
+    if (Func->empty())
+      continue;
+
+    for (Function::iterator BB = Func->begin(), E = Func->end();
+         BB != E; ++BB) {
+      for (BasicBlock::iterator Iter = BB->begin(), E = BB->end();
+           Iter != E; ) {
+        Instruction *Inst = Iter++;
+        if (CallInst *Call = dyn_cast<CallInst>(Inst)) {
+          Changed |= ConvertCall(Call);
+        } else if (isa<InvokeInst>(Inst)) {
+          report_fatal_error(
+              "ExpandSmallArguments does not handle invoke instructions");
+        }
+      }
+    }
+
+    Changed |= ConvertFunction(Func);
+  }
+  return Changed;
+}
+
+ModulePass *llvm::createExpandSmallArgumentsPass() {
+  return new ExpandSmallArguments();
+}