https://llvm.org/bugs/show_bug.cgi?id=26830
Bug ID: 26830
Summary: misaligned placement of function arguments of
over-aligned type on the stack (ABI incompatibility)
Product: clang
Version: 3.7
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: -New Bugs
Assignee: unassignedclangb...@nondot.org
Reporter: kr...@kde.org
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Testcase:
#include <xmmintrin.h>
struct X { __m128 x; };
X f(X a, X b) { return {_mm_add_ps(a.x, b.x)}; }
Compiles to (-msse -m32 -O2):
00000000 <f(X, X)>:
0:· mov 0x4(%esp),%eax
4:· movups 0x8(%esp),%xmm0
9:· movups 0x18(%esp),%xmm1
e:· addps %xmm0,%xmm1
11:· movaps %xmm1,(%eax)
14:· ret $0x4
This is incorrect according to the x86 psABI document, which states that
padding must be added so that the placement of the argument matches its
alignment. GCC compiles the code to:
00000000 <f(X, X)>:
0:· movaps 0x24(%esp),%xmm0
5:· mov 0x4(%esp),%eax
9:· addps 0x14(%esp),%xmm0
e:· movaps %xmm0,(%eax)
11:· ret $0x4
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