If a function only reads memory, then we know that...

it only reads memory!  The other change has no
functional effect, it just seems more logical to
go in order of decreasing knowledge.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@64463 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 11 insertions, 7 deletions

diff --git a/lib/Analysis/AliasAnalysis.cpp b/lib/Analysis/AliasAnalysis.cpp
index 369f2f4f90..67b2faac55 100644
--- a/lib/Analysis/AliasAnalysis.cpp
+++ b/lib/Analysis/AliasAnalysis.cpp
@@ -120,9 +120,13 @@ AliasAnalysis::getModRefBehavior(CallSite CS,
 AliasAnalysis::ModRefBehavior
 AliasAnalysis::getModRefBehavior(Function *F,
                                  std::vector<PointerAccessInfo> *Info) {
-  if (F && F->doesNotAccessMemory())
-    // Can't do better than this.
-    return DoesNotAccessMemory;
+  if (F) {
+    if (F->doesNotAccessMemory())
+      // Can't do better than this.
+      return DoesNotAccessMemory;
+    else if (F->onlyReadsMemory())
+      return OnlyReadsMemory;
+  }
   return UnknownModRefBehavior;
 }
 
@@ -130,10 +134,10 @@ AliasAnalysis::ModRefResult
 AliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
   ModRefResult Mask = ModRef;
   ModRefBehavior MRB = getModRefBehavior(CS);
-  if (MRB == OnlyReadsMemory)
-    Mask = Ref;
-  else if (MRB == DoesNotAccessMemory)
+  if (MRB == DoesNotAccessMemory)
     return NoModRef;
+  else if (MRB == OnlyReadsMemory)
+    Mask = Ref;
   else if (MRB == AliasAnalysis::AccessesArguments) {
     bool doesAlias = false;
     for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
@@ -142,7 +146,7 @@ AliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
         doesAlias = true;
         break;
       }
-    
+
     if (!doesAlias)
       return NoModRef;
   }