Re: [PATCH] xtensa: Optimize boolean evaluation or branching when EQ/NE to zero in S[IF]mode

[Max Filippov <jcmvbkbc@gmail.com>]

Hi Suwa-san,

On Sat, Jun 3, 2023 at 2:55 AM Takayuki 'January June' Suwa
<jjsuwa_sys3175@yahoo.co.jp> wrote:
>
> This patch optimizes the boolean evaluation of EQ/NE against zero
> by adding two insn_and_split patterns similar to SImode conditional
> store:
>
> "eq_zero":
>         op0 = (op1 == 0) ? 1 : 0;
>         op0 = clz(op1) >> 5;  /* optimized (requires TARGET_NSA) */
>
> "movsicc_ne0_reg_0":
>         op0 = (op1 != 0) ? op2 : 0;
>         op0 = op2; if (op1 == 0) ? op0 = op1;  /* optimized */
>
> These also work in SFmode by ignoring their sign bits, and further-
> more, the branch if EQ/NE against zero in SFmode is also done in the
> same manner.
>
> The reasons for this optimization in SFmode are:
>
>   - Only zero values (negative or non-negative) contain no bits of 1
>     with both the exponent and the mantissa.
>   - EQ/NE comparisons involving NaNs produce no signal even if they
>     are signaling.
>   - Even if the use of IEEE 754 single-precision floating-point co-
>     processor is configured (TARGET_HARD_FLOAT is true):
>         1. Load zero value to FP register
>         2. Possibly, additional FP move if the comparison target is
>            an address register
>         3. FP equality check instruction
>         4. Read the boolean register containing the result, or condi-
>            tional branch
>     As noted above, a considerable number of instructions are still
>     generated.
>
> gcc/ChangeLog:
>
>         * config/xtensa/predicates.md (const_float_0_operand):
>         Rename from obsolete "const_float_1_operand" and change the
>         constant to compare.
>         (cstoresf_cbranchsf_operand, cstoresf_cbranchsf_operator):
>         New.
>         * config/xtensa/xtensa.cc (xtensa_expand_conditional_branch):
>         Add code for EQ/NE comparison with constant zero in SFmode.
>         (xtensa_expand_scc): Added code to derive boolean evaluation
>         of EQ/NE with constant zero for comparison in SFmode.
>         (xtensa_rtx_costs): Change cost of CONST_DOUBLE with value
>         zero inside "cbranchsf4" to 0.
>         * config/xtensa/xtensa.md (cbranchsf4, cstoresf4):
>         Change "match_operator" and the third "match_operand" to the
>         ones mentioned above.
>         (movsicc_ne0_reg_zero, eq_zero): New.
> ---
>  gcc/config/xtensa/predicates.md | 19 ++++++++++--
>  gcc/config/xtensa/xtensa.cc     | 43 ++++++++++++++++++++++++++
>  gcc/config/xtensa/xtensa.md     | 53 +++++++++++++++++++++++++++++----
>  3 files changed, 106 insertions(+), 9 deletions(-)

This change results in a bunch of new testsuite failures
on configurations without FPU that are all ICEs:

+FAIL: gcc.c-torture/execute/bitfld-3.c   -O1  execution test
+FAIL: gcc.dg/atomic/c11-atomic-exec-1.c   -O1  (internal compiler
error: in extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/c11-atomic-exec-1.c   -O1  (test for excess errors)
+FAIL: gcc.dg/atomic/c11-atomic-exec-1.c   -O2  (internal compiler
error: in extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/c11-atomic-exec-1.c   -O2  (test for excess errors)
+FAIL: gcc.dg/atomic/c11-atomic-exec-1.c   -O3 -fomit-frame-pointer
-funroll-loops -fpeel-loops -ftracer -finline-functions  (internal
compiler error: in extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/c11-atomic-exec-1.c   -O3 -fomit-frame-pointer
-funroll-loops -fpeel-loops -ftracer -finline-functions  (test for
excess errors)
+FAIL: gcc.dg/atomic/c11-atomic-exec-1.c   -O3 -g  (internal compiler
error: in extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/c11-atomic-exec-1.c   -O3 -g  (test for excess errors)
+FAIL: gcc.dg/atomic/c11-atomic-exec-1.c   -Os  (internal compiler
error: in extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/c11-atomic-exec-1.c   -Os  (test for excess errors)
+FAIL: gcc.dg/atomic/c11-atomic-exec-1.c   -O2 -flto
-fno-use-linker-plugin -flto-partition=none  (internal compiler error:
in extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/c11-atomic-exec-1.c   -O2 -flto
-fno-use-linker-plugin -flto-partition=none  (test for excess errors)
+FAIL: gcc.dg/atomic/c11-atomic-exec-1.c   -O2 -flto
-fuse-linker-plugin -fno-fat-lto-objects  (internal compiler error: in
extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/c11-atomic-exec-1.c   -O2 -flto
-fuse-linker-plugin -fno-fat-lto-objects  (test for excess errors)
+FAIL: gcc.dg/atomic/c11-atomic-exec-3.c   -O1  (internal compiler
error: in extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/c11-atomic-exec-3.c   -O1  (test for excess errors)
+FAIL: gcc.dg/atomic/c11-atomic-exec-3.c   -O2  (internal compiler
error: in extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/c11-atomic-exec-3.c   -O2  (test for excess errors)
+FAIL: gcc.dg/atomic/c11-atomic-exec-3.c   -O3 -fomit-frame-pointer
-funroll-loops -fpeel-loops -ftracer -finline-functions  (internal
compiler error: in extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/c11-atomic-exec-3.c   -O3 -fomit-frame-pointer
-funroll-loops -fpeel-loops -ftracer -finline-functions  (test for
excess errors)
+FAIL: gcc.dg/atomic/c11-atomic-exec-3.c   -O3 -g  (internal compiler
error: in extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/c11-atomic-exec-3.c   -O3 -g  (test for excess errors)
+FAIL: gcc.dg/atomic/c11-atomic-exec-3.c   -Os  (internal compiler
error: in extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/c11-atomic-exec-3.c   -Os  (test for excess errors)
+FAIL: gcc.dg/atomic/c11-atomic-exec-3.c   -O2 -flto
-fno-use-linker-plugin -flto-partition=none  (internal compiler error:
in extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/c11-atomic-exec-3.c   -O2 -flto
-fno-use-linker-plugin -flto-partition=none  (test for excess errors)
+FAIL: gcc.dg/atomic/c11-atomic-exec-3.c   -O2 -flto
-fuse-linker-plugin -fno-fat-lto-objects  (internal compiler error: in
extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/c11-atomic-exec-3.c   -O2 -flto
-fuse-linker-plugin -fno-fat-lto-objects  (test for excess errors)
+FAIL: gcc.dg/atomic/pr65345-4.c   -O1  (internal compiler error: in
extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/pr65345-4.c   -O1  (test for excess errors)
+FAIL: gcc.dg/atomic/pr65345-4.c   -O2  (internal compiler error: in
extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/pr65345-4.c   -O2  (test for excess errors)
+FAIL: gcc.dg/atomic/pr65345-4.c   -O3 -g  (internal compiler error:
in extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/pr65345-4.c   -O3 -g  (test for excess errors)
+FAIL: gcc.dg/atomic/pr65345-4.c   -Os  (internal compiler error: in
extract_insn, at recog.cc:2791)
+FAIL: gcc.dg/atomic/pr65345-4.c   -Os  (test for excess errors)
+FAIL: gcc.dg/atomic/pr65345-4.c   -O2 -flto -fno-use-linker-plugin
-flto-partition=none  (internal compiler error: in extract_insn, at
recog.cc:2791)
+FAIL: gcc.dg/atomic/pr65345-4.c   -O2 -flto -fno-use-linker-plugin
-flto-partition=none  (test for excess errors)

On configuration with FPU it results in ICEs during libgfortran build, all
with the similar diagnostic:

gcc/libgfortran/intrinsics/erfc_scaled_inc.c:179:1: error: unrecognizable insn:
 179 | }
     | ^
(insn 23 22 24 2 (set (reg:CC 18 b0)
       (lt:CC (const_double:SF 0.0 [0x0.0p+0])
           (reg/v:SF 96 [ x ])))
"gcc/libgfortran/intrinsics/erfc_scaled_inc.c":111:18 -1
    (nil))
during RTL pass: vregs

-- 
Thanks.
-- Max