[Lint] Don't warn about passing alloca'd value to tail call if using byval

[uabelho]

Summary

This fixes PR35241.

When using byval, the data is effectively copied as part of the call
anyway, so the pointer returned by the alloca will not be leaked to the
callee and thus there is no reason to issue a warning.

[rnk]

lgtm with suggestion

lib/Analysis/Lint.cpp

293–294

You should be able to update this to range-based for like:

for (const Value *Arg : CS.args()) {
  ...

[uabelho]

Updated the for loop so it's range based. (Couldn't make Arg const though since the findValue
argument isn't const.)

[uabelho]

Thanks for the review. I fixed the suggestion so I'll submit this now.

lib/Analysis/Lint.cpp

for (; AI != AE; ++AI) {
           visitMemoryReference(I, Actual, DL->getTypeStoreSize(Ty),
                                DL->getABITypeAlignment(Ty), Ty,
                                MemRef::Read | MemRef::Write);
         }
       }
     }
   }
 
-  if (CS.isCall() && cast<CallInst>(CS.getInstruction())->isTailCall())
+  if (CS.isCall()) {
+    const CallInst *CI = cast<CallInst>(CS.getInstruction());
+    if (CI->isTailCall()) {
+      const AttributeList &PAL = CI->getAttributes();
+      unsigned ArgNo = 0;
       for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
            AI != AE; ++AI) {
+        // Skip ByVal arguments since they will be memcpy'd to the callee's
+        // stack anyway.
+        if (PAL.hasParamAttribute(ArgNo++, Attribute::ByVal))
+          continue;
         Value *Obj = findValue(*AI, /*OffsetOk=*/true);
         Assert(!isa<AllocaInst>(Obj),
                "Undefined behavior: Call with \"tail\" keyword references "
                "alloca",
                &I);
       }
+    }
+  }
 
 
   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
     switch (II->getIntrinsicID()) {
     default: break;
 
     // TODO: Check more intrinsics
 

test/Analysis/Lint/tail-call-byval.ll

+; RUN: opt < %s -lint -disable-output 2>&1 | FileCheck %s
+
+%s = type { i8 }
+
+declare void @f1(%s*)
+
+define void @f2() {
+entry:
+  %c = alloca %s
+  tail call void @f1(%s* %c)
+  ret void
+}
+
+; Lint should complain about the tail call passing the alloca'd value %c to f1.
+; CHECK: Undefined behavior: Call with "tail" keyword references alloca
+; CHECK-NEXT:  tail call void @f1(%s* %c)
+
+declare void @f3(%s* byval)
+
+define void @f4() {
+entry:
+  %c = alloca %s
+  tail call void @f3(%s* byval %c)
+  ret void
+}
+
+; Lint should not complain about passing the alloca'd %c since it's passed
+; byval, effectively copying the data to the stack instead of leaking the
+; pointer itself.
+; CHECK-NOT: Undefined behavior: Call with "tail" keyword references alloca
+; CHECK-NOT:  tail call void @f3(%s* byval %c)
+
+