[PATCH] D40118: [Lint] Don't warn about noalias argument aliasing if other argument is byval

[Mikael Holmén via Phabricator via llvm-commits]

uabelho created this revision.

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.


https://reviews.llvm.org/D40118

Files:
  lib/Analysis/Lint.cpp
  test/Analysis/Lint/noalias-byval.ll


Index: test/Analysis/Lint/noalias-byval.ll
===================================================================
--- /dev/null
+++ 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 }
Index: lib/Analysis/Lint.cpp
===================================================================
--- lib/Analysis/Lint.cpp
+++ lib/Analysis/Lint.cpp
@@ -265,13 +265,25 @@
         // 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()) {
+          const AttributeList &PAL =
+            CS.isCall() ?
+             cast<CallInst>(CS.getInstruction())->getAttributes() :
+             cast<InvokeInst>(CS.getInstruction())->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()) {


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