PNaCl: Impl the other atomicrmw operations: nand, max, min, umax, and umin.

lib/Transforms/NaCl/RewriteAtomics.cpp

Index: lib/Transforms/NaCl/RewriteAtomics.cpp
diff --git a/lib/Transforms/NaCl/RewriteAtomics.cpp b/lib/Transforms/NaCl/RewriteAtomics.cpp
index 652635ab0a2c85028e055476f90f6fa231af639a..858a4d7ca861d1ee0bbe3d0918cd9c18cf752d12 100644
--- a/lib/Transforms/NaCl/RewriteAtomics.cpp
+++ b/lib/Transforms/NaCl/RewriteAtomics.cpp
@@ -15,6 +15,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/ADT/Triple.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Function.h"
@@ -28,6 +29,7 @@
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/TargetRegistry.h"
 #include "llvm/Transforms/NaCl.h"
 #include <climits>
 #include <string>
@@ -75,6 +77,8 @@ public:
   void visitAtomicRMWInst(AtomicRMWInst &I);
   void visitFenceInst(FenceInst &I);
 
+  SmallVectorImpl<Function*>& getFunsWithExtraRMWOps() { return FunsWithExtraRMWOps; }
+
 private:
   Module &M;
   LLVMContext &C;
@@ -82,6 +86,13 @@ private:
   NaCl::AtomicIntrinsics AI;
   bool ModifiedModule;
 
+  /// These functions have atomic instructions which we expand with
+  /// -atomic-expand. We collect them here so we don't have to check every
+  /// instruction of every basicblock of every function in the module twice over
+  /// the coarse of the pass (under the assumption that atomic operations are
+  /// the expection rather than the rule).

[JF, 2015/07/23 22:44:38]

"exception"

+  SmallVector<Function*, 32> FunsWithExtraRMWOps;
+
   AtomicVisitor() = delete;
   AtomicVisitor(const AtomicVisitor &) = delete;
   AtomicVisitor &operator=(const AtomicVisitor &) = delete;
@@ -162,9 +173,53 @@ INITIALIZE_PASS(RewriteAtomics, "nacl-rewrite-atomics",
                 false, false)
 
 bool RewriteAtomics::runOnModule(Module &M) {
+  // rewrite nand, (u)max, (u)min rmw atomics:
+  // First we need a target machine to appease its lordship:
+
+  // Get the target specific parser.
+  std::string Error;
+  Triple TheTriple = Triple("i686-none-nacl");
+  const Target *TheTarget = TargetRegistry::lookupTarget("", TheTriple,
+                                                         Error);
+  if (!TheTarget) {
+    errs() << "Looking up 'i686-none-nacl':" << ": " << Error;
+    report_fatal_error("Did you forget to initialize the x86 target?");
+  }
+
+  // Create the target machine:
+  std::unique_ptr<TargetMachine> Target(
+      TheTarget->createTargetMachine(TheTriple.getTriple(), "generic", "",
+                                     TargetOptions(), Reloc::Default,
+                                     CodeModel::Default, CodeGenOpt::Default));
+  assert(Target != nullptr);
+
+  std::unique_ptr<FunctionPass> AtomicRMWExpander
+    (createAtomicExpandPass(Target.get()));
+
+
   AtomicVisitor AV(M, *this);
   AV.visit(M);
-  return AV.modifiedModule();
+
+  bool Changed = AV.modifiedModule();
+
+  // Expand any leftover RMW atomics:
+  // This is done after because otherwise -atomic-expand will expand stuff we're
+  // capable of expanding, leaving us with less efficient code.
+  const size_t PrevLen = AV.getFunsWithExtraRMWOps().size();
+  for(auto *F : AV.getFunsWithExtraRMWOps()) {
+    const bool Expanded = AtomicRMWExpander->runOnFunction(*F);
+    (void)Expanded;
+    assert(Expanded);
+    // revisit the function, rewriting cmpxchg to the corresponding
+    // llvm.nacl.etc.etc.
+    AV.visit(*F);
+    Changed = true;
+  }
+  // assert that -atomic-expand didn't leave things we can't expand.
+  (void)PrevLen;
+  assert(PrevLen == AV.getFunsWithExtraRMWOps().size());
+
+  return Changed;
 }
 
 template <class Instruction>
@@ -347,7 +402,11 @@ void AtomicVisitor::visitStoreInst(StoreInst &I) {
 void AtomicVisitor::visitAtomicRMWInst(AtomicRMWInst &I) {
   NaCl::AtomicRMWOperation Op;
   switch (I.getOperation()) {
-  default: report_fatal_error("unsupported atomicrmw operation: " + ToStr(I));
+  default: {
+    // delegate to -atomic-expand
+    FunsWithExtraRMWOps.push_back(I.getParent()->getParent());
+    return;
+  }
   case AtomicRMWInst::Add: Op = NaCl::AtomicAdd; break;
   case AtomicRMWInst::Sub: Op = NaCl::AtomicSub; break;
   case AtomicRMWInst::And: Op = NaCl::AtomicAnd; break;