[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

2 files changed, 58 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()) {
diff --git a/llvm/test/Analysis/Lint/noalias-byval.ll b/llvm/test/Analysis/Lint/noalias-byval.ll
new file mode 100644
index 00000000000..5b36c6d15df
--- /dev/null
+++ b/llvm/test/Analysis/Lint/noalias-byval.ll
@@ -0,0 +1,48 @@
+; RUN: opt < %s -lint -disable-output 2>&1 | FileCheck %s
+
+%s = type { i8 }
+
+; Function Attrs: argmemonly nounwind
+declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture writeonly, i8* nocapture readonly, i32, i32, i1) #0
+
+; Function Attrs: argmemonly nounwind
+declare void @llvm.memset.p0i8.i8.i32(i8* nocapture writeonly, i8, i32, i32, i1) #0
+
+declare void @f1(%s* noalias nocapture sret, %s* nocapture readnone)
+
+define void @f2() {
+entry:
+  %c = alloca %s
+  %tmp = alloca %s
+  %0 = bitcast %s* %c to i8*
+  %1 = bitcast %s* %tmp to i8*
+  call void @llvm.memset.p0i8.i8.i32(i8* %0, i8 0, i32 1, i32 1, i1 false)
+  call void @f1(%s* sret %c, %s* %c)
+  ret void
+}
+
+; Lint should complain about us passing %c to both arguments since one of them
+; is noalias.
+; CHECK: Unusual: noalias argument aliases another argument
+; CHECK-NEXT: call void @f1(%s* sret %c, %s* %c)
+
+declare void @f3(%s* noalias nocapture sret, %s* byval nocapture readnone)
+
+define void @f4() {
+entry:
+  %c = alloca %s
+  %tmp = alloca %s
+  %0 = bitcast %s* %c to i8*
+  %1 = bitcast %s* %tmp to i8*
+  call void @llvm.memset.p0i8.i8.i32(i8* %0, i8 0, i32 1, i32 1, i1 false)
+  call void @f3(%s* sret %c, %s* byval %c)
+  ret void
+}
+
+; Lint should not complain about passing %c to both arguments even if one is
+; noalias, since the other one is byval, effectively copying the data to the
+; stack instead of passing the pointer itself.
+; CHECK-NOT: Unusual: noalias argument aliases another argument
+; CHECK-NOT: call void @f3(%s* sret %c, %s* %c)
+
+attributes #0 = { argmemonly nounwind }