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* cse.c: Update comments.

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From-SVN: r94705
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Kazu Hirata 2005-02-07 17:10:27 +00:00 committed by Kazu Hirata
parent 17385e0d3b
commit 459281be31
2 changed files with 17 additions and 13 deletions
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gcc/ChangeLog
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@ -5,6 +5,8 @@
config/rs6000/altivec.md, config/rs6000/darwin-tramp.asm:
Update copyright.
* cse.c: Update comments.
2005-02-07 Richard Guenther <rguenth@gcc.gnu.org>
PR middle-end/19775

28
gcc/cse.c
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@ -80,11 +80,11 @@ Registers and "quantity numbers":
copies one register into another, we copy the quantity number.
When a register is loaded in any other way, we allocate a new
quantity number to describe the value generated by this operation.
`reg_qty' records what quantity a register is currently thought
`REG_QTY (N)' records what quantity register N is currently thought
of as containing.
All real quantity numbers are greater than or equal to zero.
If register N has not been assigned a quantity, reg_qty[N] will
If register N has not been assigned a quantity, `REG_QTY (N)' will
equal -N - 1, which is always negative.
Quantity numbers below zero do not exist and none of the `qty_table'
@ -172,18 +172,20 @@ Other expressions:
the register's new value. This sequence of circumstances is rare
within any one basic block.
The vectors `reg_tick' and `reg_in_table' are used to detect this case.
reg_tick[i] is incremented whenever a value is stored in register i.
reg_in_table[i] holds -1 if no references to register i have been
entered in the table; otherwise, it contains the value reg_tick[i] had
when the references were entered. If we want to enter a reference
and reg_in_table[i] != reg_tick[i], we must scan and remove old references.
Until we want to enter a new entry, the mere fact that the two vectors
don't match makes the entries be ignored if anyone tries to match them.
`REG_TICK' and `REG_IN_TABLE', accessors for members of
cse_reg_info, are used to detect this case. REG_TICK (i) is
incremented whenever a value is stored in register i.
REG_IN_TABLE (i) holds -1 if no references to register i have been
entered in the table; otherwise, it contains the value REG_TICK (i)
had when the references were entered. If we want to enter a
reference and REG_IN_TABLE (i) != REG_TICK (i), we must scan and
remove old references. Until we want to enter a new entry, the
mere fact that the two vectors don't match makes the entries be
ignored if anyone tries to match them.
Registers themselves are entered in the hash table as well as in
the equivalent-register chains. However, the vectors `reg_tick'
and `reg_in_table' do not apply to expressions which are simple
the equivalent-register chains. However, `REG_TICK' and
`REG_IN_TABLE' do not apply to expressions which are simple
register references. These expressions are removed from the table
immediately when they become invalid, and this can be done even if
we do not immediately search for all the expressions that refer to
@ -289,7 +291,7 @@ static rtx this_insn;
Or -1 if this register is at the end of the chain.
If reg_qty[N] == N, reg_eqv_table[N].next is undefined. */
If REG_QTY (N) == -N - 1, reg_eqv_table[N].next is undefined. */
/* Per-register equivalence chain. */
struct reg_eqv_elem