diff --git a/src/mtype.c b/src/mtype.c
index 87850601ba08..fefad7822ff4 100644
--- a/src/mtype.c
+++ b/src/mtype.c
@@ -5770,71 +5770,76 @@ Type *TypeFunction::semantic(Loc loc, Scope *sc)
 void TypeFunction::purityLevel()
 {
     TypeFunction *tf = this;
-    if (tf->purity == PUREfwdref)
-    {   /* Evaluate what kind of purity based on the modifiers for the parameters
+    if (tf->purity != PUREfwdref)
+        return;
+
+    /* Evaluate what kind of purity based on the modifiers for the parameters
+     */
+    tf->purity = PUREstrong;        // assume strong until something weakens it
+
+    size_t dim = Parameter::dim(tf->parameters);
+    if (!dim)
+        return;
+    for (size_t i = 0; i < dim; i++)
+    {
+        Parameter *fparam = Parameter::getNth(tf->parameters, i);
+        Type *t = fparam->type;
+        if (!t)
+            continue;
+
+        if (fparam->storageClass & (STClazy | STCout))
+        {
+            tf->purity = PUREweak;
+            break;
+        }
+        if (fparam->storageClass & STCref)
+        {
+            if (t->mod & MODimmutable)
+                continue;
+            if (t->mod & (MODconst | MODwild))
+            {
+                tf->purity = PUREconst;
+                continue;
+            }
+            tf->purity = PUREweak;
+            break;
+        }
+
+        t = t->baseElemOf();
+        if (!t->hasPointers())
+            continue;
+        if (t->mod & MODimmutable)
+            continue;
+
+        /* Accept immutable(T)[] and immutable(T)* as being strongly pure
          */
-        tf->purity = PUREstrong;        // assume strong until something weakens it
-        if (tf->parameters)
+        if (t->ty == Tarray || t->ty == Tpointer)
         {
-            size_t dim = Parameter::dim(tf->parameters);
-            for (size_t i = 0; i < dim; i++)
-            {   Parameter *fparam = Parameter::getNth(tf->parameters, i);
-                if (fparam->storageClass & STClazy)
-                {
-                    tf->purity = PUREweak;
-                    break;
-                }
-                if (fparam->storageClass & STCout)
-                {
-                    tf->purity = PUREweak;
-                    break;
-                }
-                if (!fparam->type)
-                    continue;
-                if (fparam->storageClass & STCref)
-                {
-                    if (!(fparam->type->mod & (MODconst | MODimmutable | MODwild)))
-                    {   tf->purity = PUREweak;
-                        break;
-                    }
-                    if (fparam->type->mod & MODconst)
-                    {   tf->purity = PUREconst;
-                        continue;
-                    }
-                }
-                Type *t = fparam->type->toBasetype();
-                if (!t->hasPointers())
-                    continue;
-                if (t->mod & MODimmutable)
-                    continue;
-                /* The rest of this is too strict; fix later.
-                 * For example, the only pointer members of a struct may be immutable,
-                 * which would maintain strong purity.
-                 */
-                if (t->mod & (MODconst | MODwild))
-                {   tf->purity = PUREconst;
-                    continue;
-                }
-                Type *tn = t->nextOf();
-                if (tn)
-                {   tn = tn->toBasetype();
-                    if (tn->ty == Tpointer || tn->ty == Tarray)
-                    {   /* Accept immutable(T)* and immutable(T)[] as being strongly pure
-                         */
-                        if (tn->mod & MODimmutable)
-                            continue;
-                        if (tn->mod & (MODconst | MODwild))
-                        {   tf->purity = PUREconst;
-                            continue;
-                        }
-                    }
-                }
-                /* Should catch delegates and function pointers, and fold in their purity
-                 */
-                tf->purity = PUREweak;          // err on the side of too strict
-                break;
+            Type *tn = t->nextOf()->toBasetype();
+            if (tn->mod & MODimmutable)
+                continue;
+            if (tn->mod & (MODconst | MODwild))
+            {
+                tf->purity = PUREconst;
+                continue;
             }
         }
+
+        /* The rest of this is too strict; fix later.
+         * For example, the only pointer members of a struct may be immutable,
+         * which would maintain strong purity.
+         */
+        if (t->mod & (MODconst | MODwild))
+        {
+            tf->purity = PUREconst;
+            continue;
+        }
+
+        /* Should catch delegates and function pointers, and fold in their purity
+         */
+
+        tf->purity = PUREweak;          // err on the side of too strict
+        break;
     }
 }
 
diff --git a/test/compilable/warn3882.d b/test/compilable/warn3882.d
new file mode 100644
index 000000000000..07e145ee6c13
--- /dev/null
+++ b/test/compilable/warn3882.d
@@ -0,0 +1,66 @@
+// PERMUTE_ARGS: -w -wi -debug
+/*
+TEST_OUTPUT:
+---
+---
+*/
+
+@safe pure nothrow void strictVoidReturn(T)(T x) {}
+@safe pure nothrow void nonstrictVoidReturn(T)(ref T x) {}
+
+void main()
+{
+    int x = 3;
+    strictVoidReturn(x);
+    nonstrictVoidReturn(x);
+}
+
+/******************************************/
+// 12619
+
+extern (C) @system nothrow pure void* memcpy(void* s1, in void* s2, size_t n);
+// -> weakly pure
+
+void test12619() pure
+{
+    ubyte[10] a, b;
+    debug memcpy(a.ptr, b.ptr, 5);  // memcpy call should have side effect
+}
+
+/******************************************/
+// 12760
+
+struct S12760(T)
+{
+    T i;
+    this(T j) inout {}
+}
+
+struct K12760
+{
+    S12760!int nullable;
+
+    this(int)
+    {
+        nullable = 0;   // weak purity
+    }
+}
+
+/******************************************/
+// 12909
+
+int f12909(immutable(int[])[int] aa) pure nothrow
+{
+    aa[0] = [];
+    return 0;
+}
+
+void test12909()
+{
+    immutable(int[])[int] aa;
+    f12909(aa);
+
+    // from 12910
+    const(int[])[int] makeAA() { return null; }  // to make r-value
+    makeAA().rehash();
+}
diff --git a/test/fail_compilation/fail3882.d b/test/fail_compilation/fail3882.d
index fa008eb8127b..b7d8a9789a90 100644
--- a/test/fail_compilation/fail3882.d
+++ b/test/fail_compilation/fail3882.d
@@ -1,21 +1,17 @@
 // REQUIRED_ARGS: -w
 // PERMUTE_ARGS: -debug
+
+/******************************************/
+// 3882
+
 /*
 TEST_OUTPUT:
 ---
-fail_compilation/fail3882.d(29): Warning: calling fail3882.strictlyPure!int.strictlyPure without side effects discards return value of type int, prepend a cast(void) if intentional
-fail_compilation/fail3882.d(33): Warning: calling fp without side effects discards return value of type int, prepend a cast(void) if intentional
+fail_compilation/fail3882.d(23): Warning: calling fail3882.strictlyPure!int.strictlyPure without side effects discards return value of type int, prepend a cast(void) if intentional
+fail_compilation/fail3882.d(27): Warning: calling fp without side effects discards return value of type int, prepend a cast(void) if intentional
 ---
 */
 
-@safe pure nothrow void strictVoidReturn(T)(T x)
-{
-}
-
-@safe pure nothrow void nonstrictVoidReturn(T)(ref T x)
-{
-}
-
 @safe pure nothrow T strictlyPure(T)(T x)
 {
     return x*x;
@@ -24,8 +20,6 @@ fail_compilation/fail3882.d(33): Warning: calling fp without side effects discar
 void main()
 {
     int x = 3;
-    strictVoidReturn(x);
-    nonstrictVoidReturn(x);
     strictlyPure(x);
 
     // 12649
@@ -34,32 +28,21 @@ void main()
 }
 
 /******************************************/
-// 12619
-
-extern (C) @system nothrow pure void* memcpy(void* s1, in void* s2, size_t n);
-// -> weakly pure
-
-void test12619() pure
-{
-    ubyte[10] a, b;
-    debug memcpy(a.ptr, b.ptr, 5);  // memcpy call should have side effect
-}
+// bugfix in TypeFunction::purityLevel
 
-/******************************************/
-// 12760
+/*
+TEST_OUTPUT:
+---
+fail_compilation/fail3882.d(46): Warning: calling fail3882.f1 without side effects discards return value of type int, prepend a cast(void) if intentional
+fail_compilation/fail3882.d(47): Warning: calling fail3882.f2 without side effects discards return value of type int, prepend a cast(void) if intentional
+---
+*/
 
-struct S12760(T)
-{
-    T i;
-    this(T j) inout {}
-}
+nothrow pure int f1(immutable(int)[] a) { return 0; }
+nothrow pure int f2(immutable(int)*  p) { return 0; }
 
-struct K12760
+void test_bug()
 {
-    S12760!int nullable;
-
-    this(int)
-    {
-        nullable = 0;   // weak purity
-    }
+    f1([]);
+    f2(null);
 }