ir: Fix wrong condition in bitfield alignment.

We should also align the allocation unit even if it's the first bitfield in the
allocation unit.

Fixes #1314

Author: emilio

src/ir/comp.rs

@@ -604,6 +604,7 @@ where
         let bitfield_size = bitfield_layout.size;
         let bitfield_align = bitfield_layout.align;
 
+        debug!("{:?}, {:?}", bitfield, bitfield_layout);
         let mut offset = unit_size_in_bits;
         if is_ms_struct {
             if unit_size_in_bits != 0 &&
@@ -627,10 +628,9 @@ where
                 unit_align = 0;
             }
         } else {
-            if offset != 0 &&
-                (bitfield_width == 0 ||
+            if bitfield_width == 0 ||
                      (offset & (bitfield_align * 8 - 1)) + bitfield_width >
-                         bitfield_size * 8)
+                         bitfield_size * 8
             {
                 offset = align_to(offset, bitfield_align * 8);
             }

tests/expectations/tests/issue-1314-bitfield-align.rs

@@ -0,0 +1,179 @@
+/* automatically generated by rust-bindgen */
+
+#![allow(dead_code, non_snake_case, non_camel_case_types, non_upper_case_globals)]
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
+pub struct __BindgenBitfieldUnit<Storage, Align>
+where
+    Storage: AsRef<[u8]> + AsMut<[u8]>,
+{
+    storage: Storage,
+    align: [Align; 0],
+}
+
+impl<Storage, Align> __BindgenBitfieldUnit<Storage, Align>
+where
+    Storage: AsRef<[u8]> + AsMut<[u8]>,
+{
+    #[inline]
+    pub fn new(storage: Storage) -> Self {
+        Self { storage, align: [] }
+    }
+
+    #[inline]
+    pub fn get_bit(&self, index: usize) -> bool {
+        debug_assert!(index / 8 < self.storage.as_ref().len());
+
+        let byte_index = index / 8;
+        let byte = self.storage.as_ref()[byte_index];
+
+        let bit_index = index % 8;
+        let mask = 1 << bit_index;
+
+        byte & mask == mask
+    }
+
+    #[inline]
+    pub fn set_bit(&mut self, index: usize, val: bool) {
+        debug_assert!(index / 8 < self.storage.as_ref().len());
+
+        let byte_index = index / 8;
+        let byte = &mut self.storage.as_mut()[byte_index];
+
+        let bit_index = index % 8;
+        let mask = 1 << bit_index;
+
+        if val {
+            *byte |= mask;
+        } else {
+            *byte &= !mask;
+        }
+    }
+
+    #[inline]
+    pub fn get(&self, bit_offset: usize, bit_width: u8) -> u64 {
+        debug_assert!(bit_width <= 64);
+        debug_assert!(bit_offset / 8 < self.storage.as_ref().len());
+        debug_assert!((bit_offset + (bit_width as usize)) / 8 <= self.storage.as_ref().len());
+
+        let mut val = 0;
+
+        for i in 0..(bit_width as usize) {
+            if self.get_bit(i + bit_offset) {
+                val |= 1 << i;
+            }
+        }
+
+        val
+    }
+
+    #[inline]
+    pub fn set(&mut self, bit_offset: usize, bit_width: u8, val: u64) {
+        debug_assert!(bit_width <= 64);
+        debug_assert!(bit_offset / 8 < self.storage.as_ref().len());
+        debug_assert!((bit_offset + (bit_width as usize)) / 8 <= self.storage.as_ref().len());
+
+        for i in 0..(bit_width as usize) {
+            let mask = 1 << i;
+            let val_bit_is_set = val & mask == mask;
+            self.set_bit(i + bit_offset, val_bit_is_set);
+        }
+    }
+}
+#[repr(C)]
+#[derive(Debug, Default, Copy, Clone)]
+pub struct S {
+    pub a: u8,
+    pub _bitfield_1: __BindgenBitfieldUnit<[u8; 2usize], u16>,
+    pub __bindgen_align: [u32; 0usize],
+}
+#[test]
+fn bindgen_test_layout_S() {
+    assert_eq!(
+        ::std::mem::size_of::<S>(),
+        4usize,
+        concat!("Size of: ", stringify!(S))
+    );
+    assert_eq!(
+        ::std::mem::align_of::<S>(),
+        4usize,
+        concat!("Alignment of ", stringify!(S))
+    );
+    assert_eq!(
+        unsafe { &(*(::std::ptr::null::<S>())).a as *const _ as usize },
+        0usize,
+        concat!("Offset of field: ", stringify!(S), "::", stringify!(a))
+    );
+}
+impl S {
+    #[inline]
+    pub fn b(&self) -> u32 {
+        unsafe { ::std::mem::transmute(self._bitfield_1.get(0usize, 15u8) as u32) }
+    }
+    #[inline]
+    pub fn set_b(&mut self, val: u32) {
+        unsafe {
+            let val: u32 = ::std::mem::transmute(val);
+            self._bitfield_1.set(0usize, 15u8, val as u64)
+        }
+    }
+    #[inline]
+    pub fn new_bitfield_1(b: u32) -> __BindgenBitfieldUnit<[u8; 2usize], u16> {
+        let mut __bindgen_bitfield_unit: __BindgenBitfieldUnit<[u8; 2usize], u16> =
+            Default::default();
+        __bindgen_bitfield_unit.set(0usize, 15u8, {
+            let b: u32 = unsafe { ::std::mem::transmute(b) };
+            b as u64
+        });
+        __bindgen_bitfield_unit
+    }
+}
+#[repr(C)]
+#[derive(Debug, Default, Copy, Clone)]
+pub struct S2 {
+    pub a: u8,
+    pub _bitfield_1: __BindgenBitfieldUnit<[u8; 2usize], u16>,
+    pub __bindgen_align: [u16; 0usize],
+}
+#[test]
+fn bindgen_test_layout_S2() {
+    assert_eq!(
+        ::std::mem::size_of::<S2>(),
+        4usize,
+        concat!("Size of: ", stringify!(S2))
+    );
+    assert_eq!(
+        ::std::mem::align_of::<S2>(),
+        2usize,
+        concat!("Alignment of ", stringify!(S2))
+    );
+    assert_eq!(
+        unsafe { &(*(::std::ptr::null::<S2>())).a as *const _ as usize },
+        0usize,
+        concat!("Offset of field: ", stringify!(S2), "::", stringify!(a))
+    );
+}
+impl S2 {
+    #[inline]
+    pub fn b(&self) -> u16 {
+        unsafe { ::std::mem::transmute(self._bitfield_1.get(0usize, 15u8) as u16) }
+    }
+    #[inline]
+    pub fn set_b(&mut self, val: u16) {
+        unsafe {
+            let val: u16 = ::std::mem::transmute(val);
+            self._bitfield_1.set(0usize, 15u8, val as u64)
+        }
+    }
+    #[inline]
+    pub fn new_bitfield_1(b: u16) -> __BindgenBitfieldUnit<[u8; 2usize], u16> {
+        let mut __bindgen_bitfield_unit: __BindgenBitfieldUnit<[u8; 2usize], u16> =
+            Default::default();
+        __bindgen_bitfield_unit.set(0usize, 15u8, {
+            let b: u16 = unsafe { ::std::mem::transmute(b) };
+            b as u64
+        });
+        __bindgen_bitfield_unit
+    }
+}

tests/headers/issue-1314-bitfield-align.h

@@ -0,0 +1,13 @@
+typedef unsigned char uint8_t;
+typedef unsigned short uint16_t;
+typedef unsigned uint32_t;
+
+typedef struct {
+  uint8_t a;
+  uint32_t b : 15;
+} S;
+
+typedef struct {
+  uint8_t a;
+  uint16_t b : 15;
+} S2;