From: Kyrylo Tkachov <[email protected]>
A round of comments that do not match the code they document.
noce_try_cmove names noce_try_store_flag_arith, a function that has never
existed. block_jumps_and_fallthru says it returns true, but it returns an
insn count or -1. dead_or_predicable documents every parameter but OTHER_BB,
noce_convert_multiple_sets_1 does not document the condition this series
started passing in, and noce_emit_cmove is described only as a helper of two
of its five callers. get_base_reg_or_constant describes only the register
case, and init_noce_multiple_sets_info never says that it fills INSN_INFO.
The noce_try_cond_arith comment is reflowed to the file's style, and the rest
are typos, a duplicated "(non-jump)", and a stray trailing space.
Comment-only.
gcc/ChangeLog:
* ifcvt.cc (first_active_insn, find_active_insn_after, block_fallthru,
noce_try_move, noce_try_sign_bit_splat, noce_try_store_flag_mask,
noce_emit_cmove, noce_try_cmove, get_base_reg_or_constant,
noce_try_cond_arith, try_emit_cmove_seq,
noce_convert_multiple_sets_1, init_noce_multiple_sets_info,
check_cond_move_block, find_if_header, block_jumps_and_fallthru,
find_if_case_2, dead_or_predicable): Fix comments.
Signed-off-by: Kyrylo Tkachov <[email protected]>
---
gcc/ifcvt.cc | 121 +++++++++++++++++++++++++++------------------------
1 file changed, 64 insertions(+), 57 deletions(-)
diff --git a/gcc/ifcvt.cc b/gcc/ifcvt.cc
index 1ee49e9c2d3..50244b73dc5 100644
--- a/gcc/ifcvt.cc
+++ b/gcc/ifcvt.cc
@@ -248,7 +248,7 @@ first_active_insn (basic_block bb)
return insn;
}
-/* Return the last non-jump active (non-jump) insn in the basic block. */
+/* Return the last non-jump active insn in the basic block. */
static rtx_insn *
last_active_insn (basic_block bb, bool skip_use_p)
@@ -316,7 +316,7 @@ find_active_insn_after (basic_block curr_bb, rtx_insn *insn)
return insn;
}
-/* Return the basic block reached by falling though the basic block BB. */
+/* Return the basic block reached by falling through the basic block BB. */
static basic_block
block_fallthru (basic_block bb)
@@ -1364,7 +1364,7 @@ noce_try_move (struct noce_if_info *if_info)
|| HONOR_SIGNED_ZEROS (if_info->x))
return false;
- /* Check whether the operands of the comparison are A and in
+ /* Check whether the operands of the comparison are A and B, in
either order. */
if ((rtx_equal_p (if_info->a, XEXP (cond, 0))
&& rtx_equal_p (if_info->b, XEXP (cond, 1)))
@@ -1396,7 +1396,7 @@ noce_try_move (struct noce_if_info *if_info)
/* If a sign bit test is selecting across constants, we may be able
to generate efficient code utilizing the -1/0 result of a sign
- bit splat idiom.
+ bit splat idiom.
Do this before trying the generalized conditional move as these
(when applicable) are hopefully faster than a conditional move. */
@@ -2285,7 +2285,11 @@ noce_try_store_flag_mask (struct noce_if_info *if_info)
return false;
}
-/* Helper function for noce_try_cmove and noce_try_cmove_arith. */
+/* Emit a conditional move selecting VTRUE or VFALSE into X, and return the
+ destination it landed in, or NULL_RTX on failure. CODE, CMP_A and CMP_B
+ give the canonicalized comparison. CC_CMP and REV_CC_CMP, when given, are
+ the non-canonicalized condition and its reverse, which let a target emit
+ the move without materializing its own compare. */
static rtx
noce_emit_cmove (struct noce_if_info *if_info, rtx x, enum rtx_code code,
@@ -2407,9 +2411,9 @@ noce_simple_cmove_operand_p (rtx x)
return CONSTANT_P (x) || register_operand (x, VOIDmode);
}
-/* Try only simple constants and registers here. More complex cases
- are handled in noce_try_cmove_arith after noce_try_store_flag_arith
- has had a go at it. */
+/* Try only simple constants and registers here. More complex cases are
+ handled in noce_try_cmove_arith, which the dispatch table reaches after
+ the store-flag matchers have had a go. */
static bool
noce_try_cmove (struct noce_if_info *if_info)
@@ -3463,8 +3467,9 @@ noce_operand_known_extended_p (rtx x, machine_mode
outer_mode,
return false;
}
-/* Helper function to return REG itself,
- otherwise NULL_RTX for other RTX_CODE. */
+/* Return the register or constant that EXP selects on: EXP itself for a
+ register or a constant, the inner register of a subreg, and NULL_RTX for
+ anything else. */
static rtx
get_base_reg_or_constant (rtx exp)
@@ -3478,29 +3483,31 @@ get_base_reg_or_constant (rtx exp)
return NULL_RTX;
}
-/* Try to covert if-then-else with conditional zero,
- returning TURE on success or FALSE on failure.
- IF_INFO describes the if-conversion scenario under consideration.
+/* Try to convert if-then-else with conditional zero, returning TRUE on
+ success or FALSE on failure. IF_INFO describes the if-conversion scenario
+ under consideration.
- It verifies the branch structure on left and transforms it into branchless
- sequence on the right, with a backend provided conditional zero or orig for
- operand z. If true, tmp is z, 0 otherwise (y op 0 is same as y for most
op).
+ It verifies the branch structure on the left and transforms it into the
+ branchless sequence on the right, with a backend-provided conditional zero
+ or orig for operand z. If true, tmp is z, 0 otherwise (y op 0 is the same
+ as y for most op).
- if (cond) | tmp = cond ? z : 0
- x = y op z | x = y op tmp
- else |
- x = y |
+ if (cond) | tmp = cond ? z : 0
+ x = y op z | x = y op tmp
+ else |
+ x = y |
- AND is special as it needs to be handled differently.
+ AND is special as it needs to be handled differently.
- tmp = !cond ? y : 0
- x = (y & z) | tmp
- Also for AND try:
- tmp = cond ? z : -1
- x = y op tmp
- To see if it is cheaper to produce `!cond ? y : 0`
- or `cond ? z : -1`.
- */
+ tmp = !cond ? y : 0
+ x = (y & z) | tmp
+
+ Also for AND try:
+
+ tmp = cond ? z : -1
+ x = y op tmp
+
+ to see if it is cheaper to produce `!cond ? y : 0` or `cond ? z : -1`. */
static bool
noce_try_cond_arith (struct noce_if_info *if_info)
@@ -4280,11 +4287,11 @@ noce_convert_multiple_sets (struct noce_if_info
*if_info)
return true;
}
-/* Try to emit the multiple-set conversion described by IF_INFO. INSN_INFO
- holds THEN_COUNT then-arm entries followed by entries for the else-only
- definitions recorded in ELSE_ONLY_INDICES. For a diamond,
- evaluate ELSE_INSN_INFO first and retain its final values for the
- conditional moves.
+/* Try to emit the multiple-set conversion described by IF_INFO, selecting on
+ the already decoded jump condition COND. INSN_INFO holds THEN_COUNT
+ then-arm entries followed by entries for the else-only definitions recorded
+ in ELSE_ONLY_INDICES. For a diamond, evaluate ELSE_INSN_INFO first and
+ retain its final values for the conditional moves.
LAST_NEEDS_COMPARISON is -1 on the first attempt. Record in it the last set
that needs a temporary to preserve the comparison, then use that boundary
@@ -4627,9 +4634,9 @@ noce_convert_multiple_sets_1 (noce_if_info *if_info, rtx
cond,
return true;
}
-/* Find local swap-style idioms in BB and mark the first insn (1)
- that is only a temporary as not needing a conditional move as
- it is going to be dead afterwards anyway.
+/* Fill INSN_INFO with one entry per active insn in BB. Find local swap-style
+ idioms and mark the first insn (1) that is only a temporary as not needing
+ a conditional move, as it is going to be dead afterwards anyway.
(1) int tmp = a;
a = b;
@@ -4642,18 +4649,17 @@ noce_convert_multiple_sets_1 (noce_if_info *if_info,
rtx cond,
a = cond ? b : a_old;
b = cond ? tmp : b_old;
- Additionally, store the index of insns like (2) when a subsequent
- SET reads from their destination.
+ Additionally, store the index of insns like (2) when a subsequent
+ SET reads from their destination.
- (2) int c = a;
- int d = c;
+ (2) int c = a;
+ int d = c;
- ifcvt
- -->
+ ifcvt
+ -->
- c = cond ? a : c_old;
- d = cond ? d : c; // Need to use c rather than c_old here.
-*/
+ c = cond ? a : c_old;
+ d = cond ? d : c; // Need to use c rather than c_old here. */
static void
init_noce_multiple_sets_info (basic_block bb,
@@ -5198,8 +5204,8 @@ noce_process_if_block (struct noce_if_info *if_info)
/* Check whether a block is suitable for conditional move conversion.
Every insn must be a simple set of a register to a constant or a
register. For each assignment, store the value in the pointer map
- VALS, keyed indexed by register pointer, then store the register
- pointer in REGS. COND is the condition we will test. */
+ VALS, keyed by register pointer, then store the register pointer in
+ REGS. COND is the condition we will test. */
static bool
check_cond_move_block (basic_block bb,
@@ -5822,10 +5828,10 @@ find_if_header (basic_block test_bb, int pass)
return ce_info.test_bb;
}
-/* Return true if a block has two edges, one of which falls through to the next
- block, and the other jumps to a specific block, so that we can tell if the
- block is part of an && test or an || test. Returns either -1 or the number
- of non-note, non-jump, non-USE/CLOBBER insns in the block. */
+/* CUR_BB has two edges, one falling through to the next block and one
+ jumping to TARGET_BB, so it can be part of an && test or an || test.
+ Return the number of non-note, non-jump, non-USE/CLOBBER insns in it, or
+ -1 if CUR_BB is not of that form. */
static int
block_jumps_and_fallthru (basic_block cur_bb, basic_block target_bb)
@@ -6555,11 +6561,12 @@ find_if_case_2 (basic_block test_bb, edge then_edge,
edge else_edge)
/* Used by the code above to perform the actual rtl transformations.
Return TRUE if successful.
- TEST_BB is the block containing the conditional branch. MERGE_BB
- is the block containing the code to manipulate. DEST_EDGE is an
- edge representing a jump to the join block; after the conversion,
- TEST_BB should be branching to its destination.
- REVERSEP is true if the sense of the branch should be reversed. */
+ TEST_BB is the block containing the conditional branch. MERGE_BB is the
+ block containing the code to manipulate. OTHER_BB is the other successor
+ of TEST_BB, the one the code is being moved past. DEST_EDGE is an edge
+ representing a jump to the join block; after the conversion, TEST_BB should
+ be branching to its destination. REVERSEP is true if the sense of the
+ branch should be reversed. */
static bool
dead_or_predicable (basic_block test_bb, basic_block merge_bb,
--
2.50.1 (Apple Git-155)
