1815e313a8
cprop1 pass does not consider paradoxical subreg and for (insn 22) claims
that it equals 8 elements of HImodeby setting REG_EQUAL note:
(insn 21 19 22 4 (set (reg:V4QI 98)
(mem/u/c:V4QI (symbol_ref/u:DI ("*.LC1") [flags 0x2]) [0 S4 A32])) "pr110206.c":12:42 1530 {*movv4qi_internal}
(expr_list:REG_EQUAL (const_vector:V4QI [
(const_int -52 [0xffffffffffffffcc]) repeated x4
])
(nil)))
(insn 22 21 23 4 (set (reg:V8HI 100)
(zero_extend:V8HI (vec_select:V8QI (subreg:V16QI (reg:V4QI 98) 0)
(parallel [
(const_int 0 [0])
(const_int 1 [0x1])
(const_int 2 [0x2])
(const_int 3 [0x3])
(const_int 4 [0x4])
(const_int 5 [0x5])
(const_int 6 [0x6])
(const_int 7 [0x7])
])))) "pr110206.c":12:42 7471 {sse4_1_zero_extendv8qiv8hi2}
(expr_list:REG_EQUAL (const_vector:V8HI [
(const_int 204 [0xcc]) repeated x8
])
(expr_list:REG_DEAD (reg:V4QI 98)
(nil))))
We rely on the "undefined" vals to have a specific value (from the earlier
REG_EQUAL note) but actual code generation doesn't ensure this (it doesn't
need to). That said, the issue isn't the constant folding per-se but that
we do not actually constant fold but register an equality that doesn't hold.
PR target/110206
gcc/ChangeLog:
* fwprop.cc (contains_paradoxical_subreg_p): Move to ...
* rtlanal.cc (contains_paradoxical_subreg_p): ... here.
* rtlanal.h (contains_paradoxical_subreg_p): Add prototype.
* cprop.cc (try_replace_reg): Do not set REG_EQUAL note
when the original source contains a paradoxical subreg.
gcc/testsuite/ChangeLog:
* gcc.target/i386/pr110206.c: New test.
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