[llvm-commits] [llvm] r61753 - /llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp

[Duncan Sands]

Author: baldrick
Date: Mon Jan  5 15:19:53 2009
New Revision: 61753

URL: http://llvm.org/viewvc/llvm-project?rev=61753&view=rev
Log:
When checking if an Argument escapes, check if
the argument is marked nocapture - no need to
analyze the argument if the answer is already
known!

Modified:
    llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp

Modified: llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp?rev=61753&r1=61752&r2=61753&view=diff

==============================================================================
--- llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp Mon Jan  5 15:19:53 2009
@@ -35,10 +35,11 @@
 // Useful predicates
 //===----------------------------------------------------------------------===//
 
-// Determine if an AllocationInst instruction escapes from the function it is
-// contained in. If it does not escape, there is no way for another function to
-// mod/ref it.  We do this by looking at its uses and determining if the uses
-// can escape (recursively).
+// Determine if a value escapes from the function it is contained in (being
+// returned by the function does not count as escaping here).  If a value local
+// to the function does not escape, there is no way another function can mod/ref
+// it.  We do this by looking at its uses and determining if they can escape
+// (recursively).
 static bool AddressMightEscape(const Value *V) {
   for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
        UI != E; ++UI) {
@@ -161,12 +162,17 @@
   // If this is a local allocation, check to see if it escapes.
   if (isa<AllocationInst>(V) || isNoAliasCall(V))
     return !AddressMightEscape(V);
-      
+
   // If this is an argument that corresponds to a byval or noalias argument,
-  // it can't escape either.
+  // then it has not escaped before entering the function.  Check if it escapes
+  // inside the function.
   if (const Argument *A = dyn_cast<Argument>(V))
-    if (A->hasByValAttr() || A->hasNoAliasAttr())
+    if (A->hasByValAttr() || A->hasNoAliasAttr()) {
+      // Don't bother analyzing arguments already known not to escape.
+      if (A->hasNoCaptureAttr())
+        return true;
       return !AddressMightEscape(V);
+    }
   return false;
 }