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alias.c: Clarify some comments. 

* alias.c: Clarify some comments.
	(record_base_value): REGNO is unsigned.
	* rtl.h (record_base_value): Likewise.

From-SVN: r34051
This commit is contained in:
Richard Kenner 2000-05-20 16:03:41 +00:00 committed by Richard Kenner
parent dc1618bcad
commit ac3d966803
3 changed files with 37 additions and 33 deletions
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4
gcc/ChangeLog
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@ -1,5 +1,9 @@
Sat May 20 09:30:55 2000 Richard Kenner <kenner@vlsi1.ultra.nyu.edu>
* alias.c: Clarify some comments.
(record_base_value): REGNO is unsigned.
* rtl.h (record_base_value): Likewise.
* alias.c (aliases_everything_p): Don't special-case QImode here.
* c-common.c (c_get_alias_set): Do it here.
Handle BIT_FIELD_REF by getting alias info for arg.

64
gcc/alias.c
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@ -38,8 +38,8 @@ Boston, MA 02111-1307, USA. */
/* The alias sets assigned to MEMs assist the back-end in determining
which MEMs can alias which other MEMs. In general, two MEMs in
different alias sets to not alias each other. There is one
exception, however. Consider something like:
different alias sets cannot alias each other, with one important
exception. Consider something like:
struct S {int i; double d; };
@ -53,12 +53,14 @@ Boston, MA 02111-1307, USA. */
|/_ _\|
int double
(The arrows are directed and point downwards.) If, when comparing
two alias sets, we can hold one set fixed, trace the other set
downwards, and at some point find the first set, the two MEMs can
alias one another. In this situation we say the alias set for
`struct S' is the `superset' and that those for `int' and `double'
are `subsets'.
(The arrows are directed and point downwards.)
In this situation we say the alias set for `struct S' is the
`superset' and that those for `int' and `double' are `subsets'.
To see whether two alias sets can point to the same memory, we must go
down the list of decendents of each and see if there is some alias set
in common. We need not trace past immediate decendents, however, since
we propagate all grandchildren up one level.
Alias set zero is implicitly a superset of all other alias sets.
However, this is no actual entry for alias set zero. It is an
@ -70,7 +72,7 @@ typedef struct alias_set_entry
int alias_set;
/* The children of the alias set. These are not just the immediate
children, but, in fact, all children. So, if we have:
children, but, in fact, all decendents. So, if we have:
struct T { struct S s; float f; }
@ -111,9 +113,7 @@ static int nonlocal_reference_p PARAMS ((rtx));
mems_in_disjoint_alias_sets_p (MEM1, MEM2)
/* Cap the number of passes we make over the insns propagating alias
information through set chains.
10 is a completely arbitrary choice. */
information through set chains. 10 is a completely arbitrary choice. */
#define MAX_ALIAS_LOOP_PASSES 10
/* reg_base_value[N] gives an address to which register N is related.
@ -164,25 +164,24 @@ static unsigned int reg_known_value_size;
/* Vector recording for each reg_known_value whether it is due to a
REG_EQUIV note. Future passes (viz., reload) may replace the
pseudo with the equivalent expression and so we account for the
dependences that would be introduced if that happens. */
/* ??? This is a problem only on the Convex. The REG_EQUIV notes created in
assign_parms mention the arg pointer, and there are explicit insns in the
RTL that modify the arg pointer. Thus we must ensure that such insns don't
get scheduled across each other because that would invalidate the REG_EQUIV
notes. One could argue that the REG_EQUIV notes are wrong, but solving
the problem in the scheduler will likely give better code, so we do it
here. */
dependences that would be introduced if that happens.
The REG_EQUIV notes created in assign_parms may mention the arg
pointer, and there are explicit insns in the RTL that modify the
arg pointer. Thus we must ensure that such insns don't get
scheduled across each other because that would invalidate the
REG_EQUIV notes. One could argue that the REG_EQUIV notes are
wrong, but solving the problem in the scheduler will likely give
better code, so we do it here. */
char *reg_known_equiv_p;
/* True when scanning insns from the start of the rtl to the
NOTE_INSN_FUNCTION_BEG note. */
static int copying_arguments;
/* The splay-tree used to store the various alias set entries. */
static splay_tree alias_sets;
/* Returns a pointer to the alias set entry for ALIAS_SET, if there is
such an entry, or NULL otherwise. */
@ -196,8 +195,8 @@ get_alias_set_entry (alias_set)
return sn != 0 ? ((alias_set_entry) sn->value) : 0;
}
/* Returns nonzero value if the alias sets for MEM1 and MEM2 are such
that the two MEMs cannot alias each other. */
/* Returns nonzero if the alias sets for MEM1 and MEM2 are such that
the two MEMs cannot alias each other. */
static int
mems_in_disjoint_alias_sets_p (mem1, mem2)
@ -515,26 +514,27 @@ record_set (dest, set, data)
reg_seen[regno] = 1;
}
/* Called from loop optimization when a new pseudo-register is created. */
/* Called from loop optimization when a new pseudo-register is
created. It indicates that REGNO is being set to VAL. f INVARIANT
is true then this value also describes an invariant relationship
which can be used to deduce that two registers with unknown values
are different. */
void
record_base_value (regno, val, invariant)
int regno;
unsigned int regno;
rtx val;
int invariant;
{
if ((unsigned) regno >= reg_base_value_size)
if (regno >= reg_base_value_size)
return;
/* If INVARIANT is true then this value also describes an invariant
relationship which can be used to deduce that two registers with
unknown values are different. */
if (invariant && alias_invariant)
alias_invariant[regno] = val;
if (GET_CODE (val) == REG)
{
if ((unsigned) REGNO (val) < reg_base_value_size)
if (REGNO (val) < reg_base_value_size)
reg_base_value[regno] = reg_base_value[REGNO (val)];
return;

2
gcc/rtl.h
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@ -1823,7 +1823,7 @@ extern void init_alias_once PARAMS ((void));
extern void init_alias_analysis PARAMS ((void));
extern void end_alias_analysis PARAMS ((void));
extern void record_base_value PARAMS ((int, rtx, int));
extern void record_base_value PARAMS ((unsigned int, rtx, int));
extern void record_alias_subset PARAMS ((int, int));
extern rtx addr_side_effect_eval PARAMS ((rtx, int, int));