[FunctionAttrs] Remove readonly and writeonly assertion

[luke]

Summary

There are scenarios where mutually recursive functions may cause the SCC
to contain both read only and write only functions. This removes an
assertion when adding read attributes which caused a crash with a the
provided test case, and instead just doesn't add the attributes.

[jdoerfert]

LGTM

I hope D60076 doesn't have the same problem ;)

[luke]

Hopefully not!
Also just a heads up, I don't have commit access to land this

[luke]

@jdoerfert Can you commit this?

[luke]

ping @homerdin

[xbolva00]

In D60761#1470317, @luke wrote:

Hopefully not!
Also just a heads up, I don't have commit access to land this

Can you please rebase the patch?

[luke]

Rebase

[xbolva00]

Thanks. I wanted to land it for you, but since I dont use monorepo now, it does not apply well for me.

Maybe @jdoerfert could land it for you?

[vivekvpandya]

This is already accepted. Do you want me to commit this on behalf of you?

[luke]

@vivekvpandya if possible, please

[vivekvpandya]

llvm/test/Transforms/FunctionAttrs/read-write-scc.ll

21

while running check-all after your patch I am getting this lit test failed.
I am getting string
attributes #0 = { nofree nounwind }
could you please check this against tot?

[jdoerfert]

I fixed the test and committed this.

llvm/lib/Transforms/IPO/FunctionAttrs.cpp

case MAK_WriteOnly:
       WritesMemory = true;
       break;
     case MAK_ReadNone:
       // Nothing to do!
       break;
     }
   }
 
+  // If the SCC contains both functions that read and functions that write, then
+  // we cannot add readonly attributes.
+  if (ReadsMemory && WritesMemory)
+    return false;
+
   // Success!  Functions in this SCC do not access memory, or only read memory.
   // Give them the appropriate attribute.
   bool MadeChange = false;
 
-  assert(!(ReadsMemory && WritesMemory) &&
-          "Function marked read-only and write-only");
   for (Function *F : SCCNodes) {
     if (F->doesNotAccessMemory())
       // Already perfect!
       continue;
 
     if (F->onlyReadsMemory() && ReadsMemory)
       // No change.
       continue;

llvm/test/Transforms/FunctionAttrs/read-write-scc.ll

+; RUN: opt -S -functionattrs < %s | FileCheck %s
+; RUN: opt -S -passes=function-attrs < %s | FileCheck %s
+
+@i = global i32 0
+
+define void @foo() {
+; CHECK-LABEL: define void @foo() #0 {
+  store i32 1, i32* @i
+  call void @bar()
+  ret void
+}
+
+define void @bar() {
+; CHECK-LABEL: define void @bar() #0 {
+  %i = load i32, i32* @i
+  call void @foo()
+  ret void
+}
+
+; CHECK: attributes #0 = { nounwind }