From cfaf520486463326a3904dcbb4092629fb0fc747 Mon Sep 17 00:00:00 2001 From: Hans-Peter Nilsson Date: Mon, 10 Feb 2020 17:21:13 +0100 Subject: [PATCH] cris: try to generate zero-based comparisons * config/cris/cris.c (cris_reduce_compare): New function. * config/cris/cris-protos.h (cris_reduce_compare): Add prototype. * config/cris/cris.md ("cbranch4", "cbranchdi4", "cstoredi4") (cstore4"): Apply cris_reduce_compare in expanders. The decc0ration work of the CRIS port made me look closer at the code for trivial comparisons, as in the condition for branches and conditional-stores, like in: void g(short int a, short int b) { short int c = a + b; if (c >= 0) foo (); } At -O2, the cc0 version of the CRIS port has an explicit *uneliminated* compare instruction ("cmp.w -1,$r10") instead of an (eliminated) compare against 0 (which below I'll call a zero-compare). This for the CRIS-cc0 version, but I see this also for a much older gcc, at 4.7. For the decc0rated port, the compare *is* a test against 0, eventually eliminated. To wit, for cc0 (mind the delay-slot): _g: subq 4,$sp add.w $r11,$r10 cmp.w -1,$r10 ble .L9 move $srp,[$sp] jsr _foo .L9: jump [$sp+] The compare instruction is expected to be eliminated, i.e. the following diff to the above is desired, modulo the missing sibling call, which corresponds to what I get from 4.7 and for the decc0rated port: !--- a Wed Feb 5 15:22:27 2020 !+++ b Wed Feb 5 15:22:51 2020 !@@ -1,8 +1,7 @@ ! _g: ! subq 4,$sp ! add.w $r11,$r10 !- cmp.w -1,$r10 !- ble .L9 !+ bmi .L9 ! move $srp,[$sp] ! ! jsr _foo Tracking this difference, I see that for both cc0-CRIS and the decc0rated CRIS, the comparison actually starts out as a compare against -1 at "expand" time, but is transformed for decc0rated CRIS to a zero-compare in "cse1". For CRIS-cc0 "cse1" does try to replace the compare with a zero-compare, but fails because at the same time it tries to replace the c operand with (a + b). Or some such; it fails and no other pass succeeds. I was not into fixing cc0-handling in core gcc, so I didn't look closer. BTW, at first, I was a bit surprised to see that for compares against a constant, a zero-compare is not canonical RTX for *all* conditions, and that instead only a subset of all RTX conditions against a constant are canonical, transforming one condition to the canonical one by adding 1 or -1 to the constant. It does makes sense at a closer look, but still not so much when emitting RTL. There are several places that mention in comments that emitting RTX as zero-compare is preferable, but nothing is done about it. Some generic code instead seems confused that the *target* is helped by seeing canonical RTX, or perhaps it (its authors) like me, confused about what a canonical comparison is. For example, prepare_cmp_insn calls canonicalize_comparison last before emitting the actual instructions. I see most ports for various port-specific reasons does their own massaging in their cbranch and cstore expanders. Still, the suboptimal compares *should* be fixed at expand time; better start out right than just relying on later optimizations. This kind of change is not acceptable in the current gcc development stage, at least as a change in generic code. However, it's problematic enough that I chose to fix this right now in the CRIS port. For that, I claim a possibly long-standing regression. After this, code before and after decc0ration is similar enough that I can spot compare-elimination-efforts and apply regression test-cases without them drowning in cc0-specific xfailing. I hope to eventually lift out cris_reduce_compare (renamed) into say expmed.c, called in e.g. emit_store_flag_1 (replacing the in-line code) and prepare_cmp_insn. Later. --- gcc/ChangeLog | 8 +++++ gcc/config/cris/cris-protos.h | 1 + gcc/config/cris/cris.c | 57 +++++++++++++++++++++++++++++++++++ gcc/config/cris/cris.md | 6 ++-- 4 files changed, 70 insertions(+), 2 deletions(-) diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 60bd34758c0..39de837b326 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,11 @@ +2020-02-10 Hans-Peter Nilsson + + Try to generate zero-based comparisons. + * config/cris/cris.c (cris_reduce_compare): New function. + * config/cris/cris-protos.h (cris_reduce_compare): Add prototype. + * config/cris/cris.md ("cbranch4", "cbranchdi4", "cstoredi4") + (cstore4"): Apply cris_reduce_compare in expanders. + 2020-02-10 Richard Earnshaw PR target/91913 diff --git a/gcc/config/cris/cris-protos.h b/gcc/config/cris/cris-protos.h index 2105256cc78..6f6d815678a 100644 --- a/gcc/config/cris/cris-protos.h +++ b/gcc/config/cris/cris-protos.h @@ -38,6 +38,7 @@ extern bool cris_constant_index_p (const_rtx); extern bool cris_base_p (const_rtx, bool); extern bool cris_base_or_autoincr_p (const_rtx, bool); extern bool cris_bdap_index_p (const_rtx, bool); +extern void cris_reduce_compare (rtx *, rtx *, rtx *); extern bool cris_biap_index_p (const_rtx, bool); extern bool cris_legitimate_address_p (machine_mode, rtx, bool); extern bool cris_store_multiple_op_p (rtx); diff --git a/gcc/config/cris/cris.c b/gcc/config/cris/cris.c index 01388b3d019..91cb63c01e7 100644 --- a/gcc/config/cris/cris.c +++ b/gcc/config/cris/cris.c @@ -3053,6 +3053,63 @@ cris_split_movdx (rtx *operands) return val; } +/* Try to change a comparison against a constant to be against zero, and + an unsigned compare against zero to be an equality test. Beware: + only valid for compares of integer-type operands. Also, note that we + don't use operand 0 at the moment. */ + +void +cris_reduce_compare (rtx *relp, rtx *, rtx *op1p) +{ + rtx op1 = *op1p; + rtx_code code = GET_CODE (*relp); + + /* Code lifted mostly from emit_store_flag_1. */ + switch (code) + { + case LT: + if (op1 == const1_rtx) + code = LE; + break; + case LE: + if (op1 == constm1_rtx) + code = LT; + break; + case GE: + if (op1 == const1_rtx) + code = GT; + break; + case GT: + if (op1 == constm1_rtx) + code = GE; + break; + case GEU: + if (op1 == const1_rtx) + code = NE; + break; + case LTU: + if (op1 == const1_rtx) + code = EQ; + break; + case GTU: + if (op1 == const0_rtx) + code = NE; + break; + case LEU: + if (op1 == const0_rtx) + code = EQ; + break; + default: + break; + } + + if (code != GET_CODE (*relp)) + { + *op1p = const0_rtx; + PUT_CODE (*relp, code); + } +} + /* The expander for the prologue pattern name. */ void diff --git a/gcc/config/cris/cris.md b/gcc/config/cris/cris.md index b73ea8bb78e..fd8355c23a3 100644 --- a/gcc/config/cris/cris.md +++ b/gcc/config/cris/cris.md @@ -3539,7 +3539,7 @@ (label_ref (match_operand 3 "" "")) (pc)))] "" - "") + "cris_reduce_compare (&operands[0], &operands[1], &operands[2]);") (define_expand "cbranchdi4" [(set (cc0) @@ -3552,6 +3552,7 @@ (pc)))] "" { + cris_reduce_compare (&operands[0], &operands[1], &operands[2]); if (TARGET_V32 && !REG_P (operands[1])) operands[1] = force_reg (DImode, operands[1]); if (TARGET_V32 && MEM_P (operands[2])) @@ -3652,6 +3653,7 @@ [(cc0) (const_int 0)]))] "" { + cris_reduce_compare (&operands[1], &operands[2], &operands[3]); if (TARGET_V32 && !REG_P (operands[2])) operands[2] = force_reg (DImode, operands[2]); if (TARGET_V32 && MEM_P (operands[3])) @@ -3666,7 +3668,7 @@ (match_operator:SI 1 "ordered_comparison_operator" [(cc0) (const_int 0)]))] "" - "") + "cris_reduce_compare (&operands[1], &operands[2], &operands[3]);") ;; Like bCC, we have to check the overflow bit for ;; signed conditions. -- 2.30.2