Fix selects of packed fields in GlobalStructOptimization (#6947)

We emit a select between two objects when only two objects exist of a
particular type. However, if the field is packed, we did not handle truncating the
written values.

2 files changed, 53 insertions, 2 deletions

diff --git a/src/passes/GlobalStructInference.cpp b/src/passes/GlobalStructInference.cpp
index 7526cdb76..4158db051 100644
--- a/src/passes/GlobalStructInference.cpp
+++ b/src/passes/GlobalStructInference.cpp
@@ -50,6 +50,7 @@
 
 #include <variant>
 
+#include "ir/bits.h"
 #include "ir/debuginfo.h"
 #include "ir/find_all.h"
 #include "ir/module-utils.h"
@@ -421,8 +422,9 @@ struct GlobalStructInference : public Pass {
           Expression* ret;
           if (value.isConstant()) {
             // This is known to be a constant, so simply emit an expression for
-            // that constant.
-            ret = value.getConstant().makeExpression(wasm);
+            // that constant, and handle if the field is packed.
+            auto* expr = value.getConstant().makeExpression(wasm);
+            ret = Bits::makePackedFieldGet(expr, field, curr->signed_, wasm);
           } else {
             // Otherwise, this is non-constant, so we are in the situation where
             // we want to un-nest the value out of the struct.new it is in. Note
diff --git a/test/lit/passes/gsi.wast b/test/lit/passes/gsi.wast
index 57d8137f4..299b19e00 100644
--- a/test/lit/passes/gsi.wast
+++ b/test/lit/passes/gsi.wast
@@ -1895,3 +1895,52 @@
     )
   )
 )
+
+;; Test packed fields.
+(module
+  ;; CHECK:      (type $struct (struct (field i8)))
+  (type $struct (struct (field i8)))
+
+  ;; CHECK:      (type $1 (func (result i32)))
+
+  ;; CHECK:      (global $A (ref $struct) (struct.new $struct
+  ;; CHECK-NEXT:  (i32.const 257)
+  ;; CHECK-NEXT: ))
+  (global $A (ref $struct) (struct.new $struct
+    (i32.const 257)
+  ))
+
+  ;; CHECK:      (global $B (ref $struct) (struct.new $struct
+  ;; CHECK-NEXT:  (i32.const 258)
+  ;; CHECK-NEXT: ))
+  (global $B (ref $struct) (struct.new $struct
+    (i32.const 258)
+  ))
+
+  ;; CHECK:      (func $test (type $1) (result i32)
+  ;; CHECK-NEXT:  (select
+  ;; CHECK-NEXT:   (i32.and
+  ;; CHECK-NEXT:    (i32.const 257)
+  ;; CHECK-NEXT:    (i32.const 255)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:   (i32.and
+  ;; CHECK-NEXT:    (i32.const 258)
+  ;; CHECK-NEXT:    (i32.const 255)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:   (ref.eq
+  ;; CHECK-NEXT:    (ref.as_non_null
+  ;; CHECK-NEXT:     (global.get $A)
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:    (global.get $A)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $test (result i32)
+    ;; We can infer this value is one of two things since only two objects exist
+    ;; of this type. We must emit the proper truncated value for them, as the
+    ;; values are truncated into i8.
+    (struct.get_u $struct 0
+     (global.get $A)
+    )
+  )
+)