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alias.c (MAX_ALIAS_LOOP_PASSES): Define.

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* alias.c (MAX_ALIAS_LOOP_PASSES): Define.
        (init_alias_analysis): Break out of loops after MAX_ALIAS_LOOP_PASSES.

From-SVN: r16415
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Jeffrey A Law 1997-11-10 07:12:10 +00:00 committed by Jeff Law
parent 0ff27f584b
commit ea64ef271d
2 changed files with 32 additions and 5 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
Mon Nov 10 00:05:56 1997 Jeffrey A Law (law@cygnus.com)
* alias.c (MAX_ALIAS_LOOP_PASSES): Define.
(init_alias_analysis): Break out of loops after MAX_ALIAS_LOOP_PASSES.
Sun Nov 9 02:07:16 1997 Jeffrey A Law (law@cygnus.com)
* fixinc.svr4 (__STDC__): Add another case.

32
gcc/alias.c
View File

@ -36,6 +36,12 @@ static int memrefs_conflict_p PROTO((int, rtx, int, rtx,
#define SIZE_FOR_MODE(X) (GET_MODE_SIZE (GET_MODE (X)))
/* Cap the number of passes we make over the insns propagating alias
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.
If all sets after the first add or subtract to the current value
or otherwise modify it so it does not point to a different top level
@ -962,7 +968,7 @@ void
init_alias_analysis ()
{
int maxreg = max_reg_num ();
int changed;
int changed, pass;
register int i;
register rtx insn;
rtx note;
@ -1002,10 +1008,21 @@ init_alias_analysis ()
We could propagate more information in the first pass by making use
of REG_N_SETS to determine immediately that the alias information
for a pseudo is "constant". */
for a pseudo is "constant".
A program with an uninitialized variable can cause an infinite loop
here. Instead of doing a full dataflow analysis to detect such problems
we just cap the number of iterations for the loop.
The state of the arrays for the set chain in question does not matter
since the program has undefined behavior. */
changed = 1;
while (changed)
pass = 0;
while (changed && pass < MAX_ALIAS_LOOP_PASSES)
{
/* Keep track of the pass number so we can break out of the loop. */
pass++;
/* Assume nothing will change this iteration of the loop. */
changed = 0;
@ -1130,10 +1147,15 @@ init_alias_analysis ()
In theory this loop can take as long as O(registers^2), but unless
there are very long dependency chains it will run in close to linear
time. */
time.
This loop may not be needed any longer now that the main loop does
a better job at propagating alias information. */
pass = 0;
do
{
changed = 0;
pass++;
for (i = 0; i < reg_base_value_size; i++)
{
rtx base = reg_base_value[i];
@ -1148,7 +1170,7 @@ init_alias_analysis ()
}
}
}
while (changed);
while (changed && pass < MAX_ALIAS_LOOP_PASSES);
new_reg_base_value = 0;
reg_seen = 0;