diff options
author | Roger Sayle <roger@nextmovesoftware.com> | 2022-08-05 21:05:35 +0100 |
---|---|---|
committer | Roger Sayle <roger@nextmovesoftware.com> | 2022-08-05 21:05:35 +0100 |
commit | cc01a27db5411a4fe354a97b7c86703c5bc81243 (patch) | |
tree | 20c4e5cf2e3c84ea150bfa85d4090c69a7c38ded | |
parent | 58a644cfdee53275e3d07eff0c2126dc88b87aef (diff) |
middle-end: Allow backend to expand/split double word compare to 0/-1.linaro-local/ci/tcwg_bmk_gnu_fx/gnu-master-aarch64-cpu2017-O3
This patch to the middle-end's RTL expansion reorders the code in
emit_store_flag_1 so that the backend has more control over how best
to expand/split double word equality/inequality comparisons against
zero or minus one. With the current implementation, the middle-end
always decides to lower this idiom during RTL expansion using SUBREGs
and word mode instructions, without ever consulting the backend's
machine description. Hence on x86_64, a TImode comparison against zero
is always expanded as:
(parallel [
(set (reg:DI 91)
(ior:DI (subreg:DI (reg:TI 88) 0)
(subreg:DI (reg:TI 88) 8)))
(clobber (reg:CC 17 flags))])
(set (reg:CCZ 17 flags)
(compare:CCZ (reg:DI 91)
(const_int 0 [0])))
This patch, which makes no changes to the code itself, simply reorders
the clauses in emit_store_flag_1 so that the middle-end first attempts
expansion using the target's doubleword mode cstore optab/expander,
and only if this fails, falls back to lowering to word mode operations.
On x86_64, this allows the expander to produce:
(set (reg:CCZ 17 flags)
(compare:CCZ (reg:TI 88)
(const_int 0 [0])))
which is a candidate for scalar-to-vector transformations (and
combine simplifications etc.). On targets that don't define a cstore
pattern for doubleword integer modes, there should be no change in
behaviour. For those that do, the current behaviour can be restored
(if desired) by restricting the expander/insn to not apply when the
comparison is EQ or NE, and operand[2] is either const0_rtx or
constm1_rtx.
This change just keeps RTL expansion more consistent (in philosophy).
For other doubleword comparisons, such as with operators LT and GT,
or with constants other than zero or -1, the wishes of the backend
are respected, and only if the optab expansion fails are the default
fall-back implementations using narrower integer mode operations
(and conditional jumps) used.
2022-08-05 Roger Sayle <roger@nextmovesoftware.com>
gcc/ChangeLog
* expmed.cc (emit_store_flag_1): Move code to expand double word
equality and inequality against zero or -1, using word operations,
to after trying to use the backend's cstore<mode>4 optab/expander.
-rw-r--r-- | gcc/expmed.cc | 111 |
1 files changed, 56 insertions, 55 deletions
diff --git a/gcc/expmed.cc b/gcc/expmed.cc index 9b01b5a51e7..8d7418be418 100644 --- a/gcc/expmed.cc +++ b/gcc/expmed.cc @@ -5662,63 +5662,9 @@ emit_store_flag_1 (rtx target, enum rtx_code code, rtx op0, rtx op1, break; } - /* If we are comparing a double-word integer with zero or -1, we can - convert the comparison into one involving a single word. */ - scalar_int_mode int_mode; - if (is_int_mode (mode, &int_mode) - && GET_MODE_BITSIZE (int_mode) == BITS_PER_WORD * 2 - && (!MEM_P (op0) || ! MEM_VOLATILE_P (op0))) - { - rtx tem; - if ((code == EQ || code == NE) - && (op1 == const0_rtx || op1 == constm1_rtx)) - { - rtx op00, op01; - - /* Do a logical OR or AND of the two words and compare the - result. */ - op00 = simplify_gen_subreg (word_mode, op0, int_mode, 0); - op01 = simplify_gen_subreg (word_mode, op0, int_mode, UNITS_PER_WORD); - tem = expand_binop (word_mode, - op1 == const0_rtx ? ior_optab : and_optab, - op00, op01, NULL_RTX, unsignedp, - OPTAB_DIRECT); - - if (tem != 0) - tem = emit_store_flag (NULL_RTX, code, tem, op1, word_mode, - unsignedp, normalizep); - } - else if ((code == LT || code == GE) && op1 == const0_rtx) - { - rtx op0h; - - /* If testing the sign bit, can just test on high word. */ - op0h = simplify_gen_subreg (word_mode, op0, int_mode, - subreg_highpart_offset (word_mode, - int_mode)); - tem = emit_store_flag (NULL_RTX, code, op0h, op1, word_mode, - unsignedp, normalizep); - } - else - tem = NULL_RTX; - - if (tem) - { - if (target_mode == VOIDmode || GET_MODE (tem) == target_mode) - return tem; - if (!target) - target = gen_reg_rtx (target_mode); - - convert_move (target, tem, - !val_signbit_known_set_p (word_mode, - (normalizep ? normalizep - : STORE_FLAG_VALUE))); - return target; - } - } - /* If this is A < 0 or A >= 0, we can do this by taking the ones complement of A (for GE) and shifting the sign bit to the low bit. */ + scalar_int_mode int_mode; if (op1 == const0_rtx && (code == LT || code == GE) && is_int_mode (mode, &int_mode) && (normalizep || STORE_FLAG_VALUE == 1 @@ -5764,6 +5710,7 @@ emit_store_flag_1 (rtx target, enum rtx_code code, rtx op0, rtx op1, return op0; } + /* Next try expanding this via the backend's cstore<mode>4. */ mclass = GET_MODE_CLASS (mode); FOR_EACH_MODE_FROM (compare_mode, mode) { @@ -5788,6 +5735,60 @@ emit_store_flag_1 (rtx target, enum rtx_code code, rtx op0, rtx op1, } } + /* If we are comparing a double-word integer with zero or -1, we can + convert the comparison into one involving a single word. */ + if (is_int_mode (mode, &int_mode) + && GET_MODE_BITSIZE (int_mode) == BITS_PER_WORD * 2 + && (!MEM_P (op0) || ! MEM_VOLATILE_P (op0))) + { + rtx tem; + if ((code == EQ || code == NE) + && (op1 == const0_rtx || op1 == constm1_rtx)) + { + rtx op00, op01; + + /* Do a logical OR or AND of the two words and compare the + result. */ + op00 = simplify_gen_subreg (word_mode, op0, int_mode, 0); + op01 = simplify_gen_subreg (word_mode, op0, int_mode, UNITS_PER_WORD); + tem = expand_binop (word_mode, + op1 == const0_rtx ? ior_optab : and_optab, + op00, op01, NULL_RTX, unsignedp, + OPTAB_DIRECT); + + if (tem != 0) + tem = emit_store_flag (NULL_RTX, code, tem, op1, word_mode, + unsignedp, normalizep); + } + else if ((code == LT || code == GE) && op1 == const0_rtx) + { + rtx op0h; + + /* If testing the sign bit, can just test on high word. */ + op0h = simplify_gen_subreg (word_mode, op0, int_mode, + subreg_highpart_offset (word_mode, + int_mode)); + tem = emit_store_flag (NULL_RTX, code, op0h, op1, word_mode, + unsignedp, normalizep); + } + else + tem = NULL_RTX; + + if (tem) + { + if (target_mode == VOIDmode || GET_MODE (tem) == target_mode) + return tem; + if (!target) + target = gen_reg_rtx (target_mode); + + convert_move (target, tem, + !val_signbit_known_set_p (word_mode, + (normalizep ? normalizep + : STORE_FLAG_VALUE))); + return target; + } + } + return 0; } |