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api_cpp.h: Fix alignas declaration following ChainedStruct. 

On 32bit Windows clang warns that alignas(ChainedStruct) uint64_t
forces the uint64_t to have a smaller alignment than it naturally has.
Fix this by making the alignas decoration take the max of
alignof(ChainedStruct) and alignof(first member).

Bug: dawn:1465
Change-Id: Ia5b73fc1be1fa56f36c5c360e719ef2a1dff7dd1
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/94940
Auto-Submit: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Takahiro <hogehoge@gachapin.jp>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
This commit is contained in:
Corentin Wallez 2022-06-29 17:37:41 +00:00 committed by Dawn LUCI CQ
parent cf52af7b0f
commit 7a64127a41
2 changed files with 13 additions and 4 deletions
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12
generator/templates/api_cpp.h
View File

@ -27,6 +27,12 @@
namespace {{metadata.namespace}} {
namespace detail {
constexpr size_t ConstexprMax(size_t a, size_t b) {
return a > b ? a : b;
}
} // namespace detail
{% set c_prefix = metadata.c_prefix %}
{% for constant in by_category["constant"] %}
{% set type = as_cppType(constant.type.name) %}
@ -232,8 +238,10 @@ namespace {{metadata.namespace}} {
{% for member in type.members %}
{% set member_declaration = as_annotated_cppType(member) + render_cpp_default_value(member) %}
{% if type.chained and loop.first %}
//* Align the first member to ChainedStruct to match the C struct layout.
alignas(ChainedStruct{{Out}}) {{member_declaration}};
//* Align the first member after ChainedStruct to match the C struct layout.
//* It has to be aligned both to its natural and ChainedStruct's alignment.
static constexpr size_t kFirstMemberAlignment = detail::ConstexprMax(alignof(ChainedStruct{{out}}), alignof({{decorate("", as_cppType(member.type.name), member)}}));
alignas(kFirstMemberAlignment) {{member_declaration}};
{% else %}
{{member_declaration}};
{% endif %}

5
generator/templates/dawn/native/api_structs.h
View File

@ -64,8 +64,9 @@ namespace {{native_namespace}} {
{% for member in type.members %}
{% set member_declaration = as_annotated_frontendType(member) + render_cpp_default_value(member) %}
{% if type.chained and loop.first %}
//* Align the first member to ChainedStruct to match the C struct layout.
alignas(ChainedStruct) {{member_declaration}};
//* Align the first member after ChainedStruct to match the C struct layout.
//* It has to be aligned both to its natural and ChainedStruct's alignment.
alignas({{namespace}}::{{as_cppType(type.name)}}::kFirstMemberAlignment) {{member_declaration}};
{% else %}
{{member_declaration}};
{% endif %}