Remove padding for over-aligned structs when we support repr(align).

Before repr(align), we could only safely guarantee up to 8-bytes of alignment (I
think the pointer-width check is a more conservative way of doing that, in
practice, because I _think_ u64 is 8-byte aligned even for smaller targets).

So when we may generate a potentially-under-aligned struct, we always used to
pad it so as to guarantee that at least the size (and thus reads from rust for
C-allocated structs) was fine.

But if we support repr(align), then the above is always unneeded.

10 files changed, 9 insertions, 17 deletions

diff --git a/src/codegen/struct_layout.rs b/src/codegen/struct_layout.rs
index 3c03ff11..45e779c9 100644
--- a/src/codegen/struct_layout.rs
+++ b/src/codegen/struct_layout.rs
@@ -258,6 +258,11 @@ impl<'a> StructLayoutTracker<'a> {
         }
 
         let padding_bytes = layout.size - self.latest_offset;
+        if padding_bytes == 0 {
+            return None;
+        }
+
+        let repr_align = self.ctx.options().rust_features().repr_align;
 
         // We always pad to get to the correct size if the struct is one of
         // those we can't align properly.
@@ -265,12 +270,10 @@ impl<'a> StructLayoutTracker<'a> {
         // Note that if the last field we saw was a bitfield, we may need to pad
         // regardless, because bitfields don't respect alignment as strictly as
         // other fields.
-        if padding_bytes > 0 &&
-            (padding_bytes >= layout.align ||
-                (self.last_field_was_bitfield &&
-                    padding_bytes >=
-                        self.latest_field_layout.unwrap().align) ||
-                layout.align > self.ctx.target_pointer_size())
+        if padding_bytes >= layout.align ||
+             (self.last_field_was_bitfield &&
+              padding_bytes >= self.latest_field_layout.unwrap().align) ||
+             (!repr_align && layout.align > self.ctx.target_pointer_size())
         {
             let layout = if self.is_packed {
                 Layout::new(padding_bytes, 1)
diff --git a/tests/expectations/tests/issue-1291.rs b/tests/expectations/tests/issue-1291.rs
index 64166917..81b29f7d 100644
--- a/tests/expectations/tests/issue-1291.rs
+++ b/tests/expectations/tests/issue-1291.rs
@@ -26,7 +26,6 @@ pub struct RTCRay {
     pub geomID: ::std::os::raw::c_uint,
     pub primID: ::std::os::raw::c_uint,
     pub instID: ::std::os::raw::c_uint,
-    pub __bindgen_padding_0: [u32; 3usize],
 }
 #[test]
 fn bindgen_test_layout_RTCRay() {
diff --git a/tests/expectations/tests/issue-648-derive-debug-with-padding.rs b/tests/expectations/tests/issue-648-derive-debug-with-padding.rs
index cb5ce74e..cb404650 100644
--- a/tests/expectations/tests/issue-648-derive-debug-with-padding.rs
+++ b/tests/expectations/tests/issue-648-derive-debug-with-padding.rs
@@ -16,7 +16,6 @@
 #[derive(Copy, Clone)]
 pub struct NoDebug {
     pub c: ::std::os::raw::c_char,
-    pub __bindgen_padding_0: [u8; 63usize],
 }
 #[test]
 fn bindgen_test_layout_NoDebug() {
@@ -61,7 +60,6 @@ impl ::std::cmp::PartialEq for NoDebug {
 pub struct ShouldDeriveDebugButDoesNot {
     pub c: [::std::os::raw::c_char; 32usize],
     pub d: ::std::os::raw::c_char,
-    pub __bindgen_padding_0: [u8; 31usize],
 }
 #[test]
 fn bindgen_test_layout_ShouldDeriveDebugButDoesNot() {
diff --git a/tests/expectations/tests/layout_array.rs b/tests/expectations/tests/layout_array.rs
index 597f03d5..3e0142d0 100644
--- a/tests/expectations/tests/layout_array.rs
+++ b/tests/expectations/tests/layout_array.rs
@@ -68,7 +68,6 @@ pub struct rte_mempool_ops {
     pub dequeue: rte_mempool_dequeue_t,
     ///< Get qty of available objs.
     pub get_count: rte_mempool_get_count,
-    pub __bindgen_padding_0: [u64; 7usize],
 }
 #[test]
 fn bindgen_test_layout_rte_mempool_ops() {
diff --git a/tests/expectations/tests/layout_array_too_long.rs b/tests/expectations/tests/layout_array_too_long.rs
index 2cd154af..5d84f053 100644
--- a/tests/expectations/tests/layout_array_too_long.rs
+++ b/tests/expectations/tests/layout_array_too_long.rs
@@ -163,7 +163,6 @@ pub struct ip_frag_pkt {
     pub last_idx: u32,
     ///< fragments
     pub frags: [ip_frag; 4usize],
-    pub __bindgen_padding_0: [u64; 6usize],
 }
 #[repr(C)]
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
diff --git a/tests/expectations/tests/layout_kni_mbuf.rs b/tests/expectations/tests/layout_kni_mbuf.rs
index b554aed5..19e82571 100644
--- a/tests/expectations/tests/layout_kni_mbuf.rs
+++ b/tests/expectations/tests/layout_kni_mbuf.rs
@@ -33,7 +33,6 @@ pub struct rte_kni_mbuf {
     pub pad3: [::std::os::raw::c_char; 8usize],
     pub pool: *mut ::std::os::raw::c_void,
     pub next: *mut ::std::os::raw::c_void,
-    pub __bindgen_padding_1: [u64; 5usize],
 }
 #[test]
 fn bindgen_test_layout_rte_kni_mbuf() {
diff --git a/tests/expectations/tests/layout_large_align_field.rs b/tests/expectations/tests/layout_large_align_field.rs
index 3b3e82cd..55a05fe5 100644
--- a/tests/expectations/tests/layout_large_align_field.rs
+++ b/tests/expectations/tests/layout_large_align_field.rs
@@ -193,7 +193,6 @@ pub struct ip_frag_pkt {
     pub last_idx: u32,
     ///< fragments
     pub frags: [ip_frag; 4usize],
-    pub __bindgen_padding_0: [u64; 6usize],
 }
 #[repr(C)]
 #[derive(Debug, Copy, Clone)]
@@ -417,7 +416,6 @@ pub struct ip_frag_tbl_stat {
     pub fail_total: u64,
     ///< # of 'no space' add failures.
     pub fail_nospace: u64,
-    pub __bindgen_padding_0: [u64; 2usize],
 }
 #[test]
 fn bindgen_test_layout_ip_frag_tbl_stat() {
diff --git a/tests/expectations/tests/layout_mbuf.rs b/tests/expectations/tests/layout_mbuf.rs
index 51e5526e..d0149b10 100644
--- a/tests/expectations/tests/layout_mbuf.rs
+++ b/tests/expectations/tests/layout_mbuf.rs
@@ -178,7 +178,6 @@ pub struct rte_mbuf {
     pub priv_size: u16,
     /// Timesync flags for use with IEEE1588.
     pub timesync: u16,
-    pub __bindgen_padding_0: [u32; 7usize],
 }
 /// 16-bit Reference counter.
 /// It should only be accessed using the following functions:
diff --git a/tests/expectations/tests/libclang-5/call-conv-field.rs b/tests/expectations/tests/libclang-5/call-conv-field.rs
index 3286ac46..9cb9606f 100644
--- a/tests/expectations/tests/libclang-5/call-conv-field.rs
+++ b/tests/expectations/tests/libclang-5/call-conv-field.rs
@@ -14,7 +14,6 @@ pub struct JNINativeInterface_ {
     pub GetVersion: ::std::option::Option<
         unsafe extern "stdcall" fn(env: *mut ::std::os::raw::c_void) -> ::std::os::raw::c_int,
     >,
-    pub __bindgen_padding_0: u32,
     pub __hack: ::std::os::raw::c_ulonglong,
 }
 #[test]
diff --git a/tests/expectations/tests/unknown_attr.rs b/tests/expectations/tests/unknown_attr.rs
index d7c8134c..0c0eeff1 100644
--- a/tests/expectations/tests/unknown_attr.rs
+++ b/tests/expectations/tests/unknown_attr.rs
@@ -14,7 +14,6 @@ pub struct max_align_t {
     pub __clang_max_align_nonce1: ::std::os::raw::c_longlong,
     pub __bindgen_padding_0: u64,
     pub __clang_max_align_nonce2: ::std::os::raw::c_longlong,
-    pub __bindgen_padding_1: u64,
 }
 #[test]
 fn bindgen_test_layout_max_align_t() {