[PATCH] llvm.noalias - Add IRBuilder support

[Philip Reames]

================
Comment at: include/llvm/IR/IRBuilder.h:449
@@ +448,3 @@
+  /// \brief Create an noalias intrinsic.
+  Instruction *CreateNoAlias(Value *Ptr, MDNode *ScopeTag);
+
----------------
CreateNoAlias sounds confusing.  Maybe, CreateNoAliasMarker?  CreateNoAliasIntrinsic?

================
Comment at: lib/IR/IRBuilder.cpp:190
@@ +189,3 @@
+Instruction *IRBuilderBase::CreateNoAlias(Value *Ptr, MDNode *ScopeTag) {
+  // FIXME: We can currently mangle just about everything, but not literal
+  // structs (for those, bitcast to i8*).
----------------
I would rather see you just bitcast everything.  Having one weird special case when we're moving to unified pointers anyways seems unjustified.

Very minor preference here; feel free to ignore.

================
Comment at: lib/IR/IRBuilder.cpp:201
@@ +200,3 @@
+  Value *Ops[] = { CPtr, MetadataAsValue::get(Context, ScopeTag) };
+  Module *M = BB->getParent()->getParent();
+  Value *FnNoAlias = Intrinsic::getDeclaration(M, Intrinsic::noalias, Types);
----------------
Use getModule

================
Comment at: lib/IR/IRBuilder.cpp:204
@@ +203,3 @@
+  Instruction *Ret = createCallHelper(FnNoAlias, Ops, this);
+  cast<CallInst>(Ret)->setDoesNotThrow();
+
----------------
If the original pointer is noalias, should the return also be noalias?  I note that this is a different noalias per discussion on another thread.  Slightly confusing to say the least.

Other attributes: nonnull, dereferenceable, etc..?  I'd be fine with instcombine rules instead.  

================
Comment at: lib/IR/IRBuilder.cpp:208
@@ +207,3 @@
+    BitCastInst *BCI = new BitCastInst(Ret, Ptr->getType(), "");
+    BB->getInstList().insert(InsertPt, BCI);
+    SetInstDebugLocation(BCI);
----------------
Using BitCastInst::Create might simplify these two lines.

http://reviews.llvm.org/D9378

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