https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66754
H.J. Lu <hjl.tools at gmail dot com> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution|--- |INVALID --- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> --- Here is a testcase without -mregparm=N: [hjl@gnu-tools-1 pr66754]$ cat x.i extern void abort(void); typedef double __v2df __attribute__ ((__vector_size__ (16))); __v2df val; void foo (char *name, __v2df x, __v2df y, __v2df z) { if (!__builtin_ia32_comisdeq (z, val)) abort(); } void bar (char *name, ...) { __builtin_apply(foo, __builtin_apply_args(), 64); } int main(void) { __v2df x = { 3.1, 3.2 }; __v2df y = { 2.1, 5.2 }; __v2df z = { 1.1, 7.2 }; val = z; bar("eeee", x, y, z); return 0; } [hjl@gnu-tools-1 pr66754]$ make /export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc -B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -m32 -msse2 -S -o x.s x.i /export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc -B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -g -m32 -msse2 -o x x.s ./x Makefile:12: recipe for target 'all' failed make: *** [all] Aborted (core dumped) [hjl@gnu-tools-1 pr66754]$ The vector parameters have the same issue. All arguments of vararg functions argument are passed on stack while the first 3 vector arguments are passed in registers for non-vararg functions.