[llvm] [tblgen] Fix behavior of !isa to prevent premature folding (PR #130442)

[Krzysztof Drewniak via llvm-commits]

https://github.com/krzysz00 created https://github.com/llvm/llvm-project/pull/130442

The test included with this commit shows a case where, even though a record's true type was !isa<> some unrelated class, the isa<> operator wolud use the declared type of the argument it was examining in order to conclude that the !isa<> expression had to be be false.

The issues is fixed by checking to make sure that the argument to the !isa operator is fully concrete before declaring its result to be false.

>From 1b2a73eccd879349475dff61ee7966805dc40edf Mon Sep 17 00:00:00 2001
From: Krzysztof Drewniak <krzysdrewniak at gmail.com>
Date: Sat, 8 Mar 2025 14:41:00 -0800
Subject: [PATCH] [tblgen] Fix behavior of !isa to prevent premature folding

The test included with this commit shows a case where, even though a
record's true type was !isa<> some unrelated class, the isa<> operator
wolud use the declared type of the argument it was examining in order
to conclude that the !isa<> expression had to be be false.

The issues is fixed by checking to make sure that the argument to the
!isa operator is fully concrete before declaring its result to be false.
---
 llvm/lib/TableGen/Record.cpp          | 10 ++++----
 llvm/test/TableGen/isa-non-primary.td | 33 +++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 4 deletions(-)
 create mode 100644 llvm/test/TableGen/isa-non-primary.td

diff --git a/llvm/lib/TableGen/Record.cpp b/llvm/lib/TableGen/Record.cpp
index 590656786bc66..5e40c8f3cfa62 100644
--- a/llvm/lib/TableGen/Record.cpp
+++ b/llvm/lib/TableGen/Record.cpp
@@ -2094,10 +2094,12 @@ const Init *IsAOpInit::Fold() const {
       return IntInit::get(getRecordKeeper(), 1);
 
     if (isa<RecordRecTy>(CheckType)) {
-      // If the target type is not a subclass of the expression type, or if
-      // the expression has fully resolved to a record, we know that it can't
-      // be of the required type.
-      if (!CheckType->typeIsConvertibleTo(TI->getType()) || isa<DefInit>(Expr))
+      // If the target type is not a subclass of the expression type once the
+      // expression has been made concrete, or if the expression has fully
+      // resolved to a record, we know that it can't be of the required type.
+      if ((!CheckType->typeIsConvertibleTo(TI->getType()) &&
+           Expr->isConcrete()) ||
+          isa<DefInit>(Expr))
         return IntInit::get(getRecordKeeper(), 0);
     } else {
       // We treat non-record types as not castable.
diff --git a/llvm/test/TableGen/isa-non-primary.td b/llvm/test/TableGen/isa-non-primary.td
new file mode 100644
index 0000000000000..96f9dfbc29d3a
--- /dev/null
+++ b/llvm/test/TableGen/isa-non-primary.td
@@ -0,0 +1,33 @@
+// RUN: llvm-tblgen %s | FileCheck %s
+
+// CHECK: --- Defs ---
+// CHECK: def Op1 {       // Op
+// CHECK-NEXT:  string res = "yes";
+// CHECK-NEXT: }
+// CHECK: def Op2 {       // Op
+// CHECK-NEXT:  string res = "no";
+// CHECK-NEXT: }
+
+class A<int a> {
+  int x = a;
+}
+
+class B<int a> : A<a> {
+  bit y = 0;
+}
+
+class C<int a> {
+  int z = !add(a, 16);
+}
+
+class D<int a> : B<a>, C<a>;
+
+def E1 : D<5>;
+def E2 : B<2>;
+
+class Op<A value> {
+  string res = !if(!isa<C>(value), "yes", "no");
+}
+
+def Op1 : Op<E1>;
+def Op2 : Op<E2>;