Improve BasicAA CS-CS queries

BasicAA contains knowledge of certain intrinsics, such as memcpy and memset,
and uses that information to form more-accurate answers to CallSite vs. Loc
ModRef queries. Unfortunately, it did not use this information when answering
CallSite vs. CallSite queries.

Generically, when an intrinsic takes one or more pointers and the intrinsic is
marked only to read/write from its arguments, the offset/size is unknown. As a
result, the generic code that answers CallSite vs. CallSite (and CallSite vs.
Loc) queries in AA uses UnknownSize when forming Locs from an intrinsic's
arguments. While BasicAA's CallSite vs. Loc override could use more-accurate
size information for some intrinsics, it did not do the same for CallSite vs.
CallSite queries.

This change refactors the intrinsic-specific logic in BasicAA into a generic AA
query function: getArgLocation, which is overridden by BasicAA to supply the
intrinsic-specific knowledge, and used by AA's generic implementation. This
allows the intrinsic-specific knowledge to be used by both CallSite vs. Loc and
CallSite vs. CallSite queries, and simplifies the BasicAA implementation.

Currently, only one function, Mac's memset_pattern16, is handled by BasicAA
(all the rest are intrinsics). As a side-effect of this refactoring, BasicAA's
getModRefBehavior override now also returns OnlyAccessesArgumentPointees for
this function (which is an improvement).

llvm-svn: 212572

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/NoAliasAnalysis.cpp b/llvm/lib/Analysis/NoAliasAnalysis.cpp
index 4e11e50e289..139fa38b8a9 100644
--- a/llvm/lib/Analysis/NoAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/NoAliasAnalysis.cpp
@@ -15,6 +15,7 @@
 #include "llvm/Analysis/Passes.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/LLVMContext.h"
 #include "llvm/Pass.h"
 using namespace llvm;
 
@@ -53,6 +54,13 @@ namespace {
     bool pointsToConstantMemory(const Location &Loc, bool OrLocal) override {
       return false;
     }
+    Location getArgLocation(ImmutableCallSite CS, unsigned ArgIdx,
+                            ModRefResult &Mask) override {
+      Mask = ModRef;
+      return Location(CS.getArgument(ArgIdx), UnknownSize,
+                      CS.getInstruction()->getMetadata(LLVMContext::MD_tbaa));
+    }
+
     ModRefResult getModRefInfo(ImmutableCallSite CS,
                                const Location &Loc) override {
       return ModRef;