PNaCl: Add support for GCC/LLVM vector extensions

lib/Transforms/NaCl/GlobalizeConstantVectors.cpp

+//===- GlobalizeConstantVectors.cpp - Globalize constant vector -----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass replaces all constant vector operands by loads of the same
+// vector value from a constant global. After this pass functions don't
+// rely on ConstantVector and ConstantDataVector.

[jvoung (off chromium), 2014/04/16 00:10:27]

Maybe reference the FlattenGlobals pass too -- It seemed important that the
transformations were later picked up by FlattenGlobals to fully simplify
things... though I guess other passes don't talk about which other passes will
do cleanup (e.g., i1 loads getting simplified further)... so up to you.

[JF, 2014/04/16 20:48:07]

Done.

+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/InstIterator.h"
+#include "llvm/Transforms/NaCl.h"
+
+using namespace llvm;
+
+namespace {
+// Must be a ModulePass since it adds globals.
+class GlobalizeConstantVectors : public ModulePass {
+public:
+  static char ID; // Pass identification, replacement for typeid
+  GlobalizeConstantVectors() : ModulePass(ID), DL(0) {
+    initializeGlobalizeConstantVectorsPass(*PassRegistry::getPassRegistry());
+  }
+  virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+    AU.setPreservesCFG();
+    AU.addRequired<DataLayout>();
+  }
+  virtual bool runOnModule(Module &M);
+
+private:
+  typedef SmallVector<Value *, 128> Values;
+  const DataLayout *DL;
+
+  void findConstantVectors(const Function &F, Values &CVs) const;
+  void globalizeConstantVectors(Module &M, Function &F,
+                                const Values &CVs) const;
+};
+} // anonymous namespace
+
+char GlobalizeConstantVectors::ID = 0;
+INITIALIZE_PASS(GlobalizeConstantVectors, "globalize-constant-vectors",
+                "Replace constant vector operands with equivalent loads", false,
+                false)
+
+void GlobalizeConstantVectors::findConstantVectors(const Function &F,
+                                                   Values &CVs) const {
+  for (const_inst_iterator II = inst_begin(F), IE = inst_end(F); II != IE;
+       ++II) {
+    for (User::const_op_iterator OI = II->op_begin(), OE = II->op_end();
+         OI != OE; ++OI) {
+      Value *V = OI->get();
+      if (isa<ConstantVector>(V) || isa<ConstantDataVector>(V))
+        CVs.push_back(V);
+    }
+  }
+}
+
+void
+GlobalizeConstantVectors::globalizeConstantVectors(Module &M, Function &F,
+                                                   const Values &CVs) const {
+  // The first instruction in a function dominates all others, it is
+  // therefore a safe insertion point.
+  // TODO(jfb) Sink values closer to their use?
+  Instruction *FirstInst = F.getEntryBlock().getFirstNonPHI();
+  for (Values::const_iterator VI = CVs.begin(), VE = CVs.end(); VI != VE;
+       ++VI) {
+    Value *V = *VI;
+    static const char Name[] = "constant_vector";
+
+    GlobalVariable *GV = new GlobalVariable(
+        M, V->getType(), /* isConstant= */ true, GlobalValue::InternalLinkage,
+        cast<Constant>(V), Name);
+    GV->setAlignment(DL->getPrefTypeAlignment(V->getType()));
+    LoadInst *MaterializedGV = new LoadInst(GV, Name, /* isVolatile= */ false,
+                                            GV->getAlignment(), FirstInst);
+
+    for (Value::use_iterator UI = V->use_begin(), UE = V->use_end(); UI != UE;
+         ++UI) {
+      User *U = *UI;
+      if (Instruction *I = dyn_cast<Instruction>(U))
+        if (I->getParent()->getParent() != &F)
+          // Skip uses of the constant vector in other functions: we
+          // need to materialize it in every function which has a use.
+          continue;
+      if (isa<GlobalVariable>(U))
+        // Don't replace global uses of the constant vector: we just
+        // created a new one. This avoid recursive references.
+        continue;
+      for (User::op_iterator OI = U->op_begin(), OE = U->op_end(); OI != OE;
+           ++OI)
+        if (dyn_cast<Value>(*OI) == V)
+          // The current operand is a use of the constant vector,
+          // replace it with the materialized one.
+          *OI = MaterializedGV;
+    }
+  }
+}
+
+bool GlobalizeConstantVectors::runOnModule(Module &M) {
+  bool Changed = false;
+  DL = &getAnalysis<DataLayout>();
+  for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI) {
+    Function &F = *FI;
+    Values ConstantVectors;
+    findConstantVectors(F, ConstantVectors);
+    if (!ConstantVectors.empty()) {
+      Changed = true;
+      globalizeConstantVectors(M, F, ConstantVectors);
+    }
+  }
+  return Changed;
+}
+
+ModulePass *llvm::createGlobalizeConstantVectorsPass() {
+  return new GlobalizeConstantVectors();
+}