[NVPTX] Add NVVMReflect pass to allow compile-time selection of

specific code paths.

This allows us to write code like:

  if (__nvvm_reflect("FOO"))
    // Do something
  else
    // Do something else

and compile into a library, then give "FOO" a value at kernel
compile-time so the check becomes a no-op.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178416 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/NVPTX/CMakeLists.txt

@@ -22,6 +22,7 @@ set(NVPTXCodeGen_sources
   NVPTXAllocaHoisting.cpp
   NVPTXAsmPrinter.cpp
   NVPTXUtilities.cpp
+  NVVMReflect.cpp
   )
 
 add_llvm_target(NVPTXCodeGen ${NVPTXCodeGen_sources})

lib/Target/NVPTX/NVPTXTargetMachine.cpp

@@ -47,6 +47,10 @@
 
 using namespace llvm;
 
+namespace llvm {
+void initializeNVVMReflectPass(PassRegistry&);
+}
+
 extern "C" void LLVMInitializeNVPTXTarget() {
   // Register the target.
   RegisterTargetMachine<NVPTXTargetMachine32> X(TheNVPTXTarget32);
@@ -55,6 +59,9 @@ extern "C" void LLVMInitializeNVPTXTarget() {
   RegisterMCAsmInfo<NVPTXMCAsmInfo> A(TheNVPTXTarget32);
   RegisterMCAsmInfo<NVPTXMCAsmInfo> B(TheNVPTXTarget64);
 
+  // FIXME: This pass is really intended to be invoked during IR optimization,
+  // but it's very NVPTX-specific.
+  initializeNVVMReflectPass(*PassRegistry::getPassRegistry());
 }
 
 NVPTXTargetMachine::NVPTXTargetMachine(

lib/Target/NVPTX/NVVMReflect.cpp

@@ -0,0 +1,193 @@
+//===- NVVMReflect.cpp - NVVM Emulate conditional compilation -------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass replaces occurences of __nvvm_reflect("string") with an
+// integer based on -nvvm-reflect-list string=<int> option given to this pass.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/StringMap.h"
+#include "llvm/Pass.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Type.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_os_ostream.h"
+#include "llvm/Transforms/Scalar.h"
+#include <map>
+#include <sstream>
+#include <string>
+#include <vector>
+
+#define NVVM_REFLECT_FUNCTION "__nvvm_reflect"
+
+using namespace llvm;
+
+namespace llvm { void initializeNVVMReflectPass(PassRegistry &); }
+
+namespace {
+class LLVM_LIBRARY_VISIBILITY NVVMReflect : public ModulePass {
+private:
+  //std::map<std::string, int> VarMap;
+  StringMap<int> VarMap;
+  typedef std::map<std::string, int>::iterator VarMapIter;
+  Function *reflectFunction;
+
+public:
+  static char ID;
+  NVVMReflect() : ModulePass(ID) {
+    VarMap.clear();
+    reflectFunction = 0;
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const { AU.setPreservesAll(); }
+  virtual bool runOnModule(Module &);
+
+  void setVarMap();
+};
+}
+
+static cl::opt<bool>
+NVVMReflectEnabled("nvvm-reflect-enable", cl::init(true),
+                   cl::desc("NVVM reflection, enabled by default"));
+
+char NVVMReflect::ID = 0;
+INITIALIZE_PASS(NVVMReflect, "nvvm-reflect",
+                "Replace occurences of __nvvm_reflect() calls with 0/1", false,
+                false)
+
+static cl::list<std::string>
+ReflectList("nvvm-reflect-list", cl::value_desc("name=0/1"),
+            cl::desc("A list of string=num assignments, where num=0 or 1"),
+            cl::ValueRequired);
+
+/// This function does the same operation as perl's split.
+/// For example, calling this with ("a=1,b=2,c=0", ",") will
+/// return ["a=1", "b=2", "c=0"] in the return std::vector.
+static std::vector<std::string>
+Tokenize(const std::string &str, const std::string &delim) {
+  std::vector<std::string> tokens;
+
+  size_t p0 = 0, p1 = std::string::npos;
+  while (p0 != std::string::npos) {
+    p1 = str.find_first_of(delim, p0);
+    if (p1 != p0) {
+      std::string token = str.substr(p0, p1 - p0);
+      tokens.push_back(token);
+    }
+    p0 = str.find_first_not_of(delim, p1);
+  }
+
+  return tokens;
+}
+
+/// The command line can look as follows :
+/// -R a=1,b=2 -R c=3,d=0 -R e=2
+/// The strings "a=1,b=2", "c=3,d=0", "e=2" are available in the
+/// ReflectList vector. First, each of ReflectList[i] is 'split'
+/// using "," as the delimiter. Then each of this part is split
+/// using "=" as the delimiter.
+void NVVMReflect::setVarMap() {
+  for (unsigned i = 0, e = ReflectList.size(); i != e; ++i) {
+    //    DEBUG(dbgs() << "Option : "  << ReflectList[i] << std::endl);
+    std::vector<std::string> nameValList = Tokenize(ReflectList[i], ",");
+    for (unsigned j = 0, ej = nameValList.size(); j != ej; ++j) {
+      std::vector<std::string> nameValPair = Tokenize(nameValList[j], "=");
+      assert(nameValPair.size() == 2 && "name=val expected");
+      std::stringstream valstream(nameValPair[1]);
+      int val;
+      valstream >> val;
+      assert((!(valstream.fail())) && "integer value expected");
+      VarMap[nameValPair[0]] = val;
+    }
+  }
+}
+
+bool NVVMReflect::runOnModule(Module &M) {
+  if (!NVVMReflectEnabled)
+    return false;
+
+  setVarMap();
+
+  reflectFunction = M.getFunction(NVVM_REFLECT_FUNCTION);
+
+  // If reflect function is not used, then there will be
+  // no entry in the module.
+  if (reflectFunction == 0) {
+    return false;
+  }
+
+  // Validate _reflect function
+  assert(reflectFunction->isDeclaration() &&
+         "_reflect function should not have a body");
+  assert(reflectFunction->getReturnType()->isIntegerTy() &&
+         "_reflect's return type should be integer");
+
+  std::vector<Instruction *> toRemove;
+
+  // Go through the uses of reflectFunction in this Function.
+  // Each of them should a CallInst with a ConstantArray argument.
+  // First validate that. If the c-string corresponding to the
+  // ConstantArray can be found successfully, see if it can be
+  // found in VarMap. If so, replace the uses of CallInst with the
+  // value found in VarMap. If not, replace the use  with value 0.
+  for (Value::use_iterator iter = reflectFunction->use_begin(),
+                           iterEnd = reflectFunction->use_end();
+       iter != iterEnd; ++iter) {
+    assert(isa<CallInst>(*iter) && "Only a call instruction can use _reflect");
+    CallInst *reflect = cast<CallInst>(*iter);
+
+    assert((reflect->getNumOperands() == 2) &&
+           "Only one operand expect for _reflect function");
+    // In cuda, we will have an extra constant-to-generic conversion of
+    // the string.
+    const Value *conv = reflect->getArgOperand(0);
+    assert(isa<CallInst>(conv) && "Expected a const-to-gen conversion");
+    const CallInst *convcall = cast<CallInst>(conv);
+    const Value *str = convcall->getArgOperand(0);
+    assert(isa<ConstantExpr>(str) &&
+           "Format of _reflect function not recognized");
+    const ConstantExpr *gep = cast<ConstantExpr>(str);
+
+    const Value *sym = gep->getOperand(0);
+    assert(isa<Constant>(sym) && "Format of _reflect function not recognized");
+
+    const Constant *symstr = cast<Constant>(sym);
+
+    assert(isa<ConstantDataSequential>(symstr->getOperand(0)) &&
+           "Format of _reflect function not recognized");
+
+    assert(cast<ConstantDataSequential>(symstr->getOperand(0))->isCString() &&
+           "Format of _reflect function not recognized");
+
+    std::string reflectArg =
+        cast<ConstantDataSequential>(symstr->getOperand(0))->getAsString();
+
+    reflectArg = reflectArg.substr(0, reflectArg.size() - 1);
+    //    DEBUG(dbgs() << "Arg of _reflect : " << reflectArg << std::endl);
+
+    int reflectVal = 0; // The default value is 0
+    if (VarMap.find(reflectArg) != VarMap.end()) {
+      reflectVal = VarMap[reflectArg];
+    }
+    reflect->replaceAllUsesWith(
+        ConstantInt::get(reflect->getType(), reflectVal));
+    toRemove.push_back(reflect);
+  }
+  if (toRemove.size() == 0)
+    return false;
+
+  for (unsigned i = 0, e = toRemove.size(); i != e; ++i)
+    toRemove[i]->eraseFromParent();
+  return true;
+}

test/CodeGen/NVPTX/nvvm-reflect.ll

@@ -0,0 +1,34 @@
+; RUN: opt < %s -S -nvvm-reflect -nvvm-reflect-list USE_MUL=0 -O2 | FileCheck %s --check-prefix=USE_MUL_0
+; RUN: opt < %s -S -nvvm-reflect -nvvm-reflect-list USE_MUL=1 -O2 | FileCheck %s --check-prefix=USE_MUL_1
+
+@str = private addrspace(4) unnamed_addr constant [8 x i8] c"USE_MUL\00"
+
+declare i32 @__nvvm_reflect(i8*)
+declare i8* @llvm.nvvm.ptr.constant.to.gen.p0i8.p4i8(i8 addrspace(4)*)
+
+define float @foo(float %a, float %b) {
+; USE_MUL_0: define float @foo
+; USE_MUL_0-NOT: call i32 @__nvvm_reflect
+; USE_MUL_1: define float @foo
+; USE_MUL_1-NOT: call i32 @__nvvm_reflect
+  %ptr = tail call i8* @llvm.nvvm.ptr.constant.to.gen.p0i8.p4i8(i8 addrspace(4)* getelementptr inbounds ([8 x i8] addrspace(4)* @str, i32 0, i32 0))
+  %reflect = tail call i32 @__nvvm_reflect(i8* %ptr)
+  %cmp = icmp ugt i32 %reflect, 0
+  br i1 %cmp, label %use_mul, label %use_add
+
+use_mul:
+; USE_MUL_1: fmul float %a, %b
+; USE_MUL_0-NOT: fadd float %a, %b
+  %ret1 = fmul float %a, %b
+  br label %exit
+
+use_add:
+; USE_MUL_0: fadd float %a, %b
+; USE_MUL_1-NOT: fmul float %a, %b
+  %ret2 = fadd float %a, %b
+  br label %exit
+
+exit:
+  %ret = phi float [%ret1, %use_mul], [%ret2, %use_add]
+  ret float %ret
+}