Hi,

the recent optimization implemented for complex modes in:
  https://gcc.gnu.org/pipermail/gcc-patches/2022-May/595865.html
contains an oversight for big-endian platforms in the "interesting corner 
case" mentioned in the message: it uses a lowpart SUBREG when the integer 
modes have different sizes, but this does not match the semantics of the 
PARALLELs which have a bundled byte offset; this offset is always zero in the 
code path and the lowpart is not at offset zero on big-endian platforms.

Calling validate_subreg with this zero offset would fix the regression by 
disabling the optimization on big-endian platforms, so instead the attached 
fix adds the appropriate right shift for them.

This fixes the following regressions in the C testsuite on SPARC64/Linux:
FAIL: gcc.c-torture/execute/20041124-1.c   -O0  execution test
FAIL: gcc.c-torture/execute/20041124-1.c   -O1  execution test
FAIL: gcc.c-torture/execute/20041124-1.c   -O2  execution test
FAIL: gcc.c-torture/execute/20041124-1.c   -O2 -flto -fno-use-linker-plugin -
flto-partition=none  execution test
FAIL: gcc.c-torture/execute/20041124-1.c   -O2 -flto -fuse-linker-plugin -fno-
fat-lto-objects  execution test
FAIL: gcc.c-torture/execute/20041124-1.c   -O3 -g  execution test
FAIL: gcc.c-torture/execute/20041124-1.c   -Os  execution test
FAIL: gcc.dg/compat/struct-by-value-11 c_compat_x_tst.o-c_compat_y_tst.o 
execute 
FAIL: gcc.dg/compat/struct-by-value-12 c_compat_x_tst.o-c_compat_y_tst.o 
execute 
FAIL: tmpdir-gcc.dg-struct-layout-1/t027 c_compat_x_tst.o-c_compat_y_tst.o 
execute 

Tested on SPARC64/Linux, OK for the mainline?


2022-10-11  Eric Botcazou  <ebotcazou@adacore.com>

	* expr.cc (emit_group_stote): Fix handling of modes of different
	sizes for big-endian targets in latest change and add commentary.

-- 
Eric Botcazou