In memops:find_dominating_parents(), the 'load-load optimization'
(see commit cf07903a "Don't bother finding dominating loads if ...")
cause some loads simplification to be missed.
For example, with the following code:
int foo(int *i, int *j)
{
*i = 6;
*j = 1;
do {
if (*i != 6)
(*i)++;
(*i)++;
} while (*i != *j);
return *j;
}
test-linearize returns something like:
foo:
.L0:
<entry-point>
store.32 $6 -> 0[%arg1]
store.32 $1 -> 0[%arg2]
br .L1
.L1:
load.32 %r4 <- 0[%arg1]
setne.32 %r5 <- %r4, $6
br %r5, .L4, .L5
.L4:
add.32 %r8 <- %r4, $1
store.32 %r8 -> 0[%arg1]
br .L5
.L5:
load.32 %r10 <- 0[%arg1]
add.32 %r11 <- %r10, $1
store.32 %r11 -> 0[%arg1]
load.32 %r15 <- 0[%arg2]
setne.32 %r16 <- %r11, %r15
br %r16, .L1, .L6
.L6:
ret.32 %r15
where we can notice that the first load in .L5 is not needed,
the value could be retrieved from %r4 and %r8, like:
@@ -8,15 +8,17 @@
.L1:
load.32 %r4 <- 0[%arg1]
setne.32 %r5 <- %r4, $6
+ phisrc.32 %phi4 <- %r4
br %r5, .L4, .L5
.L4:
add.32 %r8 <- %r4, $1
store.32 %r8 -> 0[%arg1]
+ phisrc.32 %phi5 <- %r8
br .L5
.L5:
- load.32 %r10 <- 0[%arg1]
+ phi.32 %r10 <- %phi4, %phi5
add.32 %r11 <- %r10, $1
store.32 %r11 -> 0[%arg1]
load.32 %r15 <- 0[%arg2]
The fix essentially consists in reverting commit cf07903a but on
memops.c's version of find_dominating_parents().
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
---
memops.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
diff --git a/memops.c b/memops.c
index 6dac1f57..5efdd6f2 100644
--- a/memops.c
+++ b/memops.c
@@ -18,12 +18,10 @@
static int find_dominating_parents(pseudo_t pseudo, struct instruction *insn,
struct basic_block *bb, unsigned long generation, struct pseudo_list **dominators,
- int local, int loads)
+ int local)
{
struct basic_block *parent;
- if (bb_list_size(bb->parents) > 1)
- loads = 0;
FOR_EACH_PTR(bb->parents, parent) {
struct instruction *one;
struct instruction *br;
@@ -41,8 +39,6 @@ static int find_dominating_parents(pseudo_t pseudo, struct instruction *insn,
}
if (!dominance)
continue;
- if (one->opcode == OP_LOAD && !loads)
- continue;
goto found_dominator;
} END_FOR_EACH_PTR_REVERSE(one);
no_dominance:
@@ -50,7 +46,7 @@ no_dominance:
continue;
parent->generation = generation;
- if (!find_dominating_parents(pseudo, insn, parent, generation, dominators, local, loads))
+ if (!find_dominating_parents(pseudo, insn, parent, generation, dominators, local))
return 0;
continue;
@@ -124,7 +120,7 @@ static void simplify_loads(struct basic_block *bb)
generation = ++bb_generation;
bb->generation = generation;
dominators = NULL;
- if (find_dominating_parents(pseudo, insn, bb, generation, &dominators, local, 1)) {
+ if (find_dominating_parents(pseudo, insn, bb, generation, &dominators, local)) {
/* This happens with initial assignments to structures etc.. */
if (!dominators) {
if (local) {
--
2.11.0
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