/* Post-reload compare elimination.
- Copyright (C) 2010-2017 Free Software Foundation, Inc.
+ Copyright (C) 2010-2020 Free Software Foundation, Inc.
This file is part of GCC.
#include "tm_p.h"
#include "insn-config.h"
#include "recog.h"
+#include "emit-rtl.h"
#include "cfgrtl.h"
#include "tree-pass.h"
#include "domwalk.h"
/* The insn prior to the comparison insn that clobbers the flags. */
rtx_insn *prev_clobber;
+ /* The insn prior to the comparison insn that sets in_a REG. */
+ rtx_insn *in_a_setter;
+
/* The two values being compared. These will be either REGs or
constants. */
rtx in_a, in_b;
/* True if its inputs are still valid at the end of the block. */
bool inputs_valid;
+
+ /* Whether IN_A is wrapped in a NOT before being compared. */
+ bool not_in_a;
};
static vec<comparison *> all_compares;
+/* Return whether X is a NOT unary expression. */
+
+static bool
+is_not (rtx x)
+{
+ return GET_CODE (x) == NOT;
+}
+
+/* Strip a NOT unary expression around X, if any. */
+
+static rtx
+strip_not (rtx x)
+{
+ if (is_not (x))
+ return XEXP (x, 0);
+
+ return x;
+}
+
/* Look for a "conforming" comparison, as defined above. If valid, return
the rtx for the COMPARE itself. */
if (!REG_P (dest) || REGNO (dest) != targetm.flags_regnum)
return NULL;
- if (!REG_P (XEXP (src, 0)))
+ if (!REG_P (strip_not (XEXP (src, 0))))
return NULL;
if (CONSTANT_P (XEXP (src, 1)) || REG_P (XEXP (src, 1)))
return false;
/* Make sure the compare is redundant with the previous. */
- if (!rtx_equal_p (XEXP (compare, 0), cmp->in_a)
+ if (!rtx_equal_p (strip_not (XEXP (compare, 0)), cmp->in_a)
|| !rtx_equal_p (XEXP (compare, 1), cmp->in_b))
return false;
+ if (is_not (XEXP (compare, 0)) != cmp->not_in_a)
+ return false;
+
/* New mode must be compatible with the previous compare mode. */
- enum machine_mode new_mode
+ machine_mode new_mode
= targetm.cc_modes_compatible (GET_MODE (compare), cmp->orig_mode);
if (new_mode == VOIDmode)
edge
find_comparison_dom_walker::before_dom_children (basic_block bb)
{
- struct comparison *last_cmp;
- rtx_insn *insn, *next, *last_clobber;
- bool last_cmp_valid;
+ rtx_insn *insn, *next;
bool need_purge = false;
- bitmap killed;
-
- killed = BITMAP_ALLOC (NULL);
+ rtx_insn *last_setter[FIRST_PSEUDO_REGISTER];
/* The last comparison that was made. Will be reset to NULL
once the flags are clobbered. */
- last_cmp = NULL;
+ struct comparison *last_cmp = NULL;
/* True iff the last comparison has not been clobbered, nor
have its inputs. Used to eliminate duplicate compares. */
- last_cmp_valid = false;
+ bool last_cmp_valid = false;
/* The last insn that clobbered the flags, if that insn is of
a form that may be valid for eliminating a following compare.
To be reset to NULL once the flags are set otherwise. */
- last_clobber = NULL;
+ rtx_insn *last_clobber = NULL;
/* Propagate the last live comparison throughout the extended basic block. */
if (single_pred_p (bb))
last_cmp_valid = last_cmp->inputs_valid;
}
+ memset (last_setter, 0, sizeof (last_setter));
for (insn = BB_HEAD (bb); insn; insn = next)
{
rtx src;
if (!NONDEBUG_INSN_P (insn))
continue;
- /* Compute the set of registers modified by this instruction. */
- bitmap_clear (killed);
- df_simulate_find_defs (insn, killed);
-
src = conforming_compare (insn);
if (src)
{
last_cmp = XCNEW (struct comparison);
last_cmp->insn = insn;
last_cmp->prev_clobber = last_clobber;
- last_cmp->in_a = XEXP (src, 0);
+ last_cmp->in_a = strip_not (XEXP (src, 0));
last_cmp->in_b = XEXP (src, 1);
+ last_cmp->not_in_a = is_not (XEXP (src, 0));
last_cmp->eh_note = eh_note;
last_cmp->orig_mode = GET_MODE (src);
+ if (last_cmp->in_b == const0_rtx
+ && last_setter[REGNO (last_cmp->in_a)])
+ {
+ rtx set = single_set (last_setter[REGNO (last_cmp->in_a)]);
+ if (set && rtx_equal_p (SET_DEST (set), last_cmp->in_a))
+ last_cmp->in_a_setter = last_setter[REGNO (last_cmp->in_a)];
+ }
all_compares.safe_push (last_cmp);
/* It's unusual, but be prepared for comparison patterns that
find_flags_uses_in_insn (last_cmp, insn);
/* Notice if this instruction kills the flags register. */
- if (bitmap_bit_p (killed, targetm.flags_regnum))
- {
- /* See if this insn could be the "clobber" that eliminates
- a future comparison. */
- last_clobber = (arithmetic_flags_clobber_p (insn) ? insn : NULL);
-
- /* In either case, the previous compare is no longer valid. */
- last_cmp = NULL;
- last_cmp_valid = false;
- }
+ df_ref def;
+ FOR_EACH_INSN_DEF (def, insn)
+ if (DF_REF_REGNO (def) == targetm.flags_regnum)
+ {
+ /* See if this insn could be the "clobber" that eliminates
+ a future comparison. */
+ last_clobber = (arithmetic_flags_clobber_p (insn)
+ ? insn : NULL);
+
+ /* In either case, the previous compare is no longer valid. */
+ last_cmp = NULL;
+ last_cmp_valid = false;
+ break;
+ }
}
- /* Notice if any of the inputs to the comparison have changed. */
- if (last_cmp_valid
- && (bitmap_bit_p (killed, REGNO (last_cmp->in_a))
- || (REG_P (last_cmp->in_b)
- && bitmap_bit_p (killed, REGNO (last_cmp->in_b)))))
- last_cmp_valid = false;
+ /* Notice if any of the inputs to the comparison have changed
+ and remember last insn that sets each register. */
+ df_ref def;
+ FOR_EACH_INSN_DEF (def, insn)
+ {
+ if (last_cmp_valid
+ && (DF_REF_REGNO (def) == REGNO (last_cmp->in_a)
+ || (REG_P (last_cmp->in_b)
+ && DF_REF_REGNO (def) == REGNO (last_cmp->in_b))))
+ last_cmp_valid = false;
+ last_setter[DF_REF_REGNO (def)] = insn;
+ }
}
- BITMAP_FREE (killed);
-
/* Remember the live comparison for subsequent members of
the extended basic block. */
if (last_cmp)
df_ref def;
/* Note that the BB_HEAD is always either a note or a label, but in
- any case it means that IN_A is defined outside the block. */
+ any case it means that REG is defined outside the block. */
if (insn == bb_head)
return NULL_RTX;
if (NOTE_P (insn) || DEBUG_INSN_P (insn))
continue;
- /* Find a possible def of IN_A in INSN. */
+ /* Find a possible def of REG in INSN. */
FOR_EACH_INSN_DEF (def, insn)
if (DF_REF_REGNO (def) == REGNO (reg))
break;
- /* No definitions of IN_A; continue searching. */
+ /* No definitions of REG; continue searching. */
if (def == NULL)
continue;
- /* Bail if this is not a totally normal set of IN_A. */
+ /* Bail if this is not a totally normal set of REG. */
if (DF_REF_IS_ARTIFICIAL (def))
return NULL_RTX;
if (DF_REF_FLAGS (def) & abnormal_flags)
return NULL_RTX;
/* We've found an insn between the compare and the clobber that sets
- IN_A. Given that pass_cprop_hardreg has not yet run, we still find
+ REG. Given that pass_cprop_hardreg has not yet run, we still find
situations in which we can usefully look through a copy insn. */
rtx x = single_set (insn);
if (x == NULL_RTX)
return reg;
}
+/* Return true if it is okay to merge the comparison CMP_INSN with
+ the instruction ARITH_INSN. Both instructions are assumed to be in the
+ same basic block with ARITH_INSN appearing before CMP_INSN. This checks
+ that there are no uses or defs of the condition flags or control flow
+ changes between the two instructions. */
+
+static bool
+can_merge_compare_into_arith (rtx_insn *cmp_insn, rtx_insn *arith_insn)
+{
+ for (rtx_insn *insn = PREV_INSN (cmp_insn);
+ insn && insn != arith_insn;
+ insn = PREV_INSN (insn))
+ {
+ if (!NONDEBUG_INSN_P (insn))
+ continue;
+ /* Bail if there are jumps or calls in between. */
+ if (!NONJUMP_INSN_P (insn))
+ return false;
+
+ /* Bail on old-style asm statements because they lack
+ data flow information. */
+ if (GET_CODE (PATTERN (insn)) == ASM_INPUT)
+ return false;
+
+ df_ref ref;
+ /* Find a USE of the flags register. */
+ FOR_EACH_INSN_USE (ref, insn)
+ if (DF_REF_REGNO (ref) == targetm.flags_regnum)
+ return false;
+
+ /* Find a DEF of the flags register. */
+ FOR_EACH_INSN_DEF (ref, insn)
+ if (DF_REF_REGNO (ref) == targetm.flags_regnum)
+ return false;
+ }
+ return true;
+}
+
+/* Given two SET expressions, SET_A and SET_B determine whether they form
+ a recognizable pattern when emitted in parallel. Return that parallel
+ if so. Otherwise return NULL. */
+
+static rtx
+try_validate_parallel (rtx set_a, rtx set_b)
+{
+ rtx par = gen_rtx_PARALLEL (VOIDmode, gen_rtvec (2, set_a, set_b));
+ rtx_insn *insn = make_insn_raw (par);
+
+ if (insn_invalid_p (insn, false))
+ {
+ crtl->emit.x_cur_insn_uid--;
+ return NULL_RTX;
+ }
+
+ SET_PREV_INSN (insn) = NULL_RTX;
+ SET_NEXT_INSN (insn) = NULL_RTX;
+ INSN_LOCATION (insn) = 0;
+ return insn;
+}
+
+/* For a comparison instruction described by CMP check if it compares a
+ register with zero i.e. it is of the form CC := CMP R1, 0.
+ If it is, find the instruction defining R1 (say I1) and try to create a
+ PARALLEL consisting of I1 and the comparison, representing a flag-setting
+ arithmetic instruction. Example:
+ I1: R1 := R2 + R3
+ <instructions that don't read the condition register>
+ I2: CC := CMP R1 0
+ I2 can be merged with I1 into:
+ I1: { CC := CMP (R2 + R3) 0 ; R1 := R2 + R3 }
+ This catches cases where R1 is used between I1 and I2 and therefore
+ combine and other RTL optimisations will not try to propagate it into
+ I2. Return true if we succeeded in merging CMP. */
+
+static bool
+try_merge_compare (struct comparison *cmp)
+{
+ rtx_insn *cmp_insn = cmp->insn;
+
+ if (cmp->in_b != const0_rtx || cmp->in_a_setter == NULL)
+ return false;
+ rtx in_a = cmp->in_a;
+ df_ref use;
+
+ FOR_EACH_INSN_USE (use, cmp_insn)
+ if (DF_REF_REGNO (use) == REGNO (in_a))
+ break;
+ if (!use)
+ return false;
+
+ rtx_insn *def_insn = cmp->in_a_setter;
+ rtx set = single_set (def_insn);
+ if (!set)
+ return false;
+
+ if (!can_merge_compare_into_arith (cmp_insn, def_insn))
+ return false;
+
+ rtx src = SET_SRC (set);
+
+ /* If the source uses addressing modes with side effects, we can't
+ do the merge because we'd end up with a PARALLEL that has two
+ instances of that side effect in it. */
+ if (side_effects_p (src))
+ return false;
+
+ rtx flags = maybe_select_cc_mode (cmp, src, CONST0_RTX (GET_MODE (src)));
+ if (!flags)
+ {
+ /* We may already have a change group going through maybe_select_cc_mode.
+ Discard it properly. */
+ cancel_changes (0);
+ return false;
+ }
+
+ rtx flag_set
+ = gen_rtx_SET (flags, gen_rtx_COMPARE (GET_MODE (flags),
+ copy_rtx (src),
+ CONST0_RTX (GET_MODE (src))));
+ rtx arith_set = copy_rtx (PATTERN (def_insn));
+ rtx par = try_validate_parallel (flag_set, arith_set);
+ if (!par)
+ {
+ /* We may already have a change group going through maybe_select_cc_mode.
+ Discard it properly. */
+ cancel_changes (0);
+ return false;
+ }
+ if (!apply_change_group ())
+ return false;
+ emit_insn_after (par, def_insn);
+ delete_insn (def_insn);
+ delete_insn (cmp->insn);
+ return true;
+}
+
/* Attempt to replace a comparison with a prior arithmetic insn that can
compute the same flags value as the comparison itself. Return true if
successful, having made all rtl modifications necessary. */
static bool
try_eliminate_compare (struct comparison *cmp)
{
- rtx flags, in_a, in_b, cmp_src;
+ rtx flags, in_a, in_b, cmp_a, cmp_b;
+
+ if (try_merge_compare (cmp))
+ return true;
/* We must have found an interesting "clobber" preceding the compare. */
if (cmp->prev_clobber == NULL)
rtx x = XVECEXP (PATTERN (insn), 0, 0);
if (rtx_equal_p (SET_DEST (x), in_a))
- cmp_src = SET_SRC (x);
+ cmp_a = SET_SRC (x);
/* Also check operations with implicit extensions, e.g.:
[(set (reg:DI)
&& (GET_CODE (SET_SRC (x)) == ZERO_EXTEND
|| GET_CODE (SET_SRC (x)) == SIGN_EXTEND)
&& GET_MODE (XEXP (SET_SRC (x), 0)) == GET_MODE (in_a))
- cmp_src = XEXP (SET_SRC (x), 0);
+ cmp_a = XEXP (SET_SRC (x), 0);
/* Also check fully redundant comparisons, e.g.:
[(set (reg:SI)
&& GET_CODE (SET_SRC (x)) == MINUS
&& rtx_equal_p (XEXP (SET_SRC (x), 0), in_a)
&& rtx_equal_p (XEXP (SET_SRC (x), 1), in_b))
- cmp_src = in_a;
+ cmp_a = in_a;
+
+ else
+ return false;
+
+ /* If the source uses addressing modes with side effects, we can't
+ do the merge because we'd end up with a PARALLEL that has two
+ instances of that side effect in it. */
+ if (side_effects_p (cmp_a))
+ return false;
+ if (in_a == in_b)
+ cmp_b = cmp_a;
+ else if (rtx_equal_p (SET_DEST (x), in_b))
+ cmp_b = SET_SRC (x);
else
+ cmp_b = in_b;
+ if (side_effects_p (cmp_b))
return false;
/* Determine if we ought to use a different CC_MODE here. */
- flags = maybe_select_cc_mode (cmp, cmp_src, in_b);
+ flags = maybe_select_cc_mode (cmp, cmp_a, cmp_b);
if (flags == NULL)
flags = gen_rtx_REG (cmp->orig_mode, targetm.flags_regnum);
/* Generate a new comparison for installation in the setter. */
- rtx y = copy_rtx (cmp_src);
- y = gen_rtx_COMPARE (GET_MODE (flags), y, in_b);
+ rtx y = cmp->not_in_a
+ ? gen_rtx_NOT (GET_MODE (cmp_a), copy_rtx (cmp_a))
+ : copy_rtx (cmp_a);
+ y = gen_rtx_COMPARE (GET_MODE (flags), y, copy_rtx (cmp_b));
y = gen_rtx_SET (flags, y);
/* Canonicalize instruction to:
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