[AttributeFuncs] Consider `noundef` in `typeIncompatible`

[jdoerfert]

Summary

Drop noundef for return values that are replaced by void and make it
illegal to put noundef on a void value.

[fhahn]

llvm/test/Transforms/DeadArgElim/returned.ll

48

could you also add a test where noundef needs to be dropped? Here it seems like it is added.

[jdoerfert]

Rebase on top of D87304

[jdoerfert]

llvm/test/Transforms/DeadArgElim/returned.ll

48

Here it is dropped. I add it in the input and the output doesn't have any attributes (it's void)

[fhahn]

LGTM, thanks!

llvm/test/Transforms/DeadArgElim/returned.ll

48

Oh right, didn't look closely enough. The function gets turned into one that returns void

llvm/lib/IR/Attributes.cpp

Incompatible.addAttribute(Attribute::Nest)
         .addAttribute(Attribute::ReadNone)
         .addAttribute(Attribute::ReadOnly)
         .addAttribute(Attribute::StructRet)
         .addAttribute(Attribute::InAlloca)
         .addPreallocatedAttr(Ty)
         .addByValAttr(Ty)
         .addByRefAttr(Ty);
 
+  // Some attributes can apply to all "values" but there are no `void` values.
+  if (Ty->isVoidTy())
+    Incompatible.addAttribute(Attribute::NoUndef);
+
   return Incompatible;
 }
 
 template<typename AttrClass>
 static bool isEqual(const Function &Caller, const Function &Callee) {
   return Caller.getFnAttribute(AttrClass::getKind()) ==
          Callee.getFnAttribute(AttrClass::getKind());
 }

llvm/test/Transforms/DeadArgElim/returned.ll

 
 define internal %Ty* @test5(%Ty* %this) {
   store volatile %Ty* %this, %Ty** @dummy
   ret %Ty* %this
 }
 
 ; Drop all these attributes
 ; CHECK-LABEL: define internal void @test6
-define internal align 8 dereferenceable_or_null(2) noalias i8* @test6() {
+define internal align 8 dereferenceable_or_null(2) noundef noalias i8* @test6() {
   ret i8* null
 }
 
 define %Ty* @caller(%Ty* %this) {
   %1 = call %Ty* @test1(%Ty* %this)
   %2 = call %Ty* @test2(%Ty* %this)
   %3 = call %Ty* @test3(%Ty* %this)
   %4 = call %Ty* @test4(%Ty* %this)
 ; ...instead, drop 'returned' form the call site
 ; CHECK: call void @test5(%Ty* %this)
   %5 = call %Ty* @test5(%Ty* returned %this)
   %6 = call i8* @test6()
   ret %Ty* %this
 }

llvm/test/Verifier/align.ll

 ; RUN: not llvm-as < %s -o /dev/null 2>&1 | FileCheck %s
 
 ; CHECK: Wrong types for attribute: inalloca nest noalias nocapture nonnull readnone readonly byref(i32) byval(i32) preallocated(i32) sret(i32) align 1 dereferenceable(1) dereferenceable_or_null(1)
 ; CHECK-NEXT: @align_non_pointer1
 define void @align_non_pointer1(i32 align 4 %a) {
   ret void
 }
 
-; CHECK: Wrong types for attribute: inalloca nest noalias nocapture nonnull readnone readonly signext zeroext byref(void) byval(void) preallocated(void) sret(void) align 1 dereferenceable(1) dereferenceable_or_null(1)
+; CHECK: Wrong types for attribute: inalloca nest noalias nocapture noundef nonnull readnone readonly signext zeroext byref(void) byval(void) preallocated(void) sret(void) align 1 dereferenceable(1) dereferenceable_or_null(1)
 ; CHECK-NEXT: @align_non_pointer2
 define align 4 void @align_non_pointer2(i32 %a) {
   ret void
 }

llvm/test/Verifier/noundef.ll

+; RUN: not llvm-as < %s -o /dev/null 2>&1 | FileCheck %s
+
+; CHECK: Wrong types for attribute: inalloca nest noalias nocapture noundef nonnull readnone readonly signext zeroext byref(void) byval(void) preallocated(void) sret(void) align 1 dereferenceable(1) dereferenceable_or_null(1)
+; CHECK-NEXT: @noundef_void
+define noundef void @noundef_void() {
+  ret void
+}