[Lint] Don't warn about noalias argument aliasing if other argument is byval

Summary:
When using byval, the data is effectively copied as part of the call
anyway, so we aren't actually passing the pointer and thus there is no
reason to issue a warning.

Reviewers: rnk

Reviewed By: rnk

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D40118

llvm-svn: 321478

1 files changed, 10 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/Lint.cpp b/llvm/lib/Analysis/Lint.cpp
index 7b792ed0a2e..0e3f498cb14 100644
--- a/llvm/lib/Analysis/Lint.cpp
+++ b/llvm/lib/Analysis/Lint.cpp
@@ -265,13 +265,21 @@ void Lint::visitCallSite(CallSite CS) {
         // Check that noalias arguments don't alias other arguments. This is
         // not fully precise because we don't know the sizes of the dereferenced
         // memory regions.
-        if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy())
-          for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI)
+        if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy()) {
+          AttributeList PAL = CS.getAttributes();
+          unsigned ArgNo = 0;
+          for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI) {
+            // Skip ByVal arguments since they will be memcpy'd to the callee's
+            // stack so we're not really passing the pointer anyway.
+            if (PAL.hasParamAttribute(ArgNo++, Attribute::ByVal))
+              continue;
             if (AI != BI && (*BI)->getType()->isPointerTy()) {
               AliasResult Result = AA->alias(*AI, *BI);
               Assert(Result != MustAlias && Result != PartialAlias,
                      "Unusual: noalias argument aliases another argument", &I);
             }
+          }
+        }
 
         // Check that an sret argument points to valid memory.
         if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {