PNaCl: Add ExpandConstantExpr pass for converting ConstantExprs to Instructions

Once this pass is enabled, it will simplify the language to reduce the
set of constructs that a PNaCl translator needs to handle as part of a
stable wire format for PNaCl.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3337
TEST=test/Transforms/NaCl/expand-constantexpr.ll

Review URL: https://codereview.chromium.org/12792011

2 files changed, 113 insertions, 0 deletions

diff --git a/lib/Transforms/NaCl/CMakeLists.txt b/lib/Transforms/NaCl/CMakeLists.txt
index 5e24cc7e28..acf7656f64 100644
--- a/lib/Transforms/NaCl/CMakeLists.txt
+++ b/lib/Transforms/NaCl/CMakeLists.txt
@@ -1,4 +1,5 @@
 add_llvm_library(LLVMTransformsNaCl
+  ExpandConstantExpr.cpp
   ExpandCtors.cpp
   ExpandTls.cpp
   ExpandTlsConstantExpr.cpp
diff --git a/lib/Transforms/NaCl/ExpandConstantExpr.cpp b/lib/Transforms/NaCl/ExpandConstantExpr.cpp
new file mode 100644
index 0000000000..5ff47cb00c
--- /dev/null
+++ b/lib/Transforms/NaCl/ExpandConstantExpr.cpp
@@ -0,0 +1,112 @@
+//===- ExpandConstantExpr.cpp - Convert ConstantExprs to Instructions------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass expands out ConstantExprs into Instructions.
+//
+// Note that this only converts ConstantExprs that are referenced by
+// Instructions.  It does not convert ConstantExprs that are used as
+// initializers for global variables.
+//
+// This simplifies the language so that the PNaCl translator does not
+// need to handle ConstantExprs as part of a stable wire format for
+// PNaCl.
+//
+//===----------------------------------------------------------------------===//
+
+#include <map>
+
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/NaCl.h"
+
+using namespace llvm;
+
+static bool expandInstruction(Instruction *Inst);
+
+namespace {
+  // This is a FunctionPass because our handling of PHI nodes means
+  // that our modifications may cross BasicBlocks.
+  struct ExpandConstantExpr : public FunctionPass {
+    static char ID; // Pass identification, replacement for typeid
+    ExpandConstantExpr() : FunctionPass(ID) {
+      initializeExpandConstantExprPass(*PassRegistry::getPassRegistry());
+    }
+
+    virtual bool runOnFunction(Function &Func);
+  };
+}
+
+char ExpandConstantExpr::ID = 0;
+INITIALIZE_PASS(ExpandConstantExpr, "expand-constant-expr",
+                "Expand out ConstantExprs into Instructions",
+                false, false)
+
+static Value *expandConstantExpr(Instruction *InsertPt, ConstantExpr *Expr) {
+  Instruction *NewInst = Expr->getAsInstruction();
+  NewInst->insertBefore(InsertPt);
+  NewInst->setName("expanded");
+  expandInstruction(NewInst);
+  return NewInst;
+}
+
+static bool expandInstruction(Instruction *Inst) {
+  // A landingpad can only accept ConstantExprs, so it should remain
+  // unmodified.
+  if (isa<LandingPadInst>(Inst))
+    return false;
+
+  bool Modified = false;
+  if (PHINode *PN = dyn_cast<PHINode>(Inst)) {
+    // PHI nodes require special treatment.  A incoming block may be
+    // listed twice, but its incoming values must match so they must
+    // be converted only once.
+    std::map<BasicBlock*,Value*> Converted;
+    for (unsigned OpNum = 0; OpNum < Inst->getNumOperands(); OpNum++) {
+      if (ConstantExpr *Expr =
+          dyn_cast<ConstantExpr>(Inst->getOperand(OpNum))) {
+        Modified = true;
+        BasicBlock *Incoming = PN->getIncomingBlock(OpNum);
+        if (Converted.count(Incoming) == 0) {
+          Converted[Incoming] = expandConstantExpr(Incoming->getTerminator(),
+                                                   Expr);
+        }
+        Inst->setOperand(OpNum, Converted[Incoming]);
+      }
+    }
+    return Modified;
+  }
+
+  for (unsigned OpNum = 0; OpNum < Inst->getNumOperands(); OpNum++) {
+    if (ConstantExpr *Expr =
+        dyn_cast<ConstantExpr>(Inst->getOperand(OpNum))) {
+      Modified = true;
+      Inst->setOperand(OpNum, expandConstantExpr(Inst, Expr));
+    }
+  }
+  return Modified;
+}
+
+bool ExpandConstantExpr::runOnFunction(Function &Func) {
+  bool Modified = false;
+  for (llvm::Function::iterator BB = Func.begin(), E = Func.end();
+       BB != E;
+       ++BB) {
+    for (BasicBlock::InstListType::iterator Inst = BB->begin(), E = BB->end();
+         Inst != E;
+         ++Inst) {
+      Modified |= expandInstruction(Inst);
+    }
+  }
+  return Modified;
+}
+
+FunctionPass *llvm::createExpandConstantExprPass() {
+  return new ExpandConstantExpr();
+}