https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99670
Bug ID: 99670
Summary: IPA CP and SRA pass order issue?
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: ipa
Assignee: unassigned at gcc dot gnu.org
Reporter: rguenth at gcc dot gnu.org
CC: marxin at gcc dot gnu.org
Target Milestone: ---
struct X { int i; int j; };
int k;
static void __attribute__((noinline)) bar (int *i)
{
k = *i;
}
static void __attribute__((noinline)) foo (struct X x)
{
bar (&x.j);
}
int main()
{
struct X x;
x.i = 0;
x.j = 1;
foo (x);
}
this ends up being IPA optimized as
;; Function bar.isra (bar.isra.0, funcdef_no=3, decl_uid=1965, cgraph_uid=5,
symbol_order=5) (executed once)
__attribute__((noinline))
void bar.isra (int ISRA.3)
{
int * i;
int * i;
int _1;
<bb 3> [local count: 1073741824]:
<bb 2> [local count: 1073741824]:
_1 = ISRA.3_2(D);
k = _1;
return;
}
;; Function foo.constprop (foo.constprop.0, funcdef_no=4, decl_uid=1964,
cgraph_uid=4, symbol_order=4) (executed once)
__attribute__((noinline))
void foo.constprop (struct X x)
{
int _3;
<bb 3> [local count: 1073741824]:
<bb 2> [local count: 1073741824]:
_3 = MEM[(int *)&x + 4B];
bar.isra (_3);
return;
}
;; Function main (main, funcdef_no=2, decl_uid=1952, cgraph_uid=3,
symbol_order=3) (executed once)
int main ()
{
struct X x;
<bb 2> [local count: 1073741824]:
x.i = 0;
x.j = 1;
foo.constprop (x);
x ={v} {CLOBBER};
return 0;
}
where the odd thing is that we have a foo.constprop clone that is not in
any way modified (by IPA CP). IPA CP does figure that we pass two constant
components but somehow even though IPA SRA turns the pass-by-referece into
a pass by value the resulting constant propagation opportunity isn't
realized.
IPA CP has
Jump functions:
Jump functions of caller main/3:
callsite main/3 -> foo/2 :
param 0: UNKNOWN
Aggregate passed by value:
offset: 0, type: int, CONST: 0
offset: 32, type: int, CONST: 1
Unknown bits
Unknown VR
Jump functions of caller foo/2:
callsite foo/2 -> bar/1 :
param 0: UNKNOWN
value: 0x0, mask: 0xfffffffffffffffc
VR [1, -1]
Jump functions of caller bar/1:
Propagating constants:
Initializing lattices of main/3
Marking all lattices as BOTTOM
Initializing lattices of foo/2
Initializing lattices of bar/1
overall_size: 17
Setting dest_lattice to bottom, because type of param 0 of foo/2 is NULL or
unsuitable for bits propagation
but still does
Estimating effects for foo/2.
Estimating body: foo/2
Known to be false:
size:5 time:13.000000 nonspec time:13.000000 loops with known
iterations:0.000000 known strides:0.000000
- context independent values, size: 5, time_benefit: 0.000000
Decided to specialize for all known contexts, code not going to grow.
...
IPA decision stage:
Evaluating opportunities for foo/2.
- Creating a specialized node of foo/2 for all known contexts.
Accounting size:2.00, time:11.00 on predicate exec:(true)
the new node is foo.constprop/4.
Aggregate replacements: 0[0]=0, 0[32]=1
...
Modification phase of node foo.constprop/4
Aggregate replacements: 0[0]=0, 0[32]=1
__attribute__((noinline))
void foo.constprop (struct X x)
{
<bb 3> [local count: 1073741824]:
<bb 2> [local count: 1073741824]:
bar (&x.j);
return;
I wonder if IPA CP and IPA SRA should work more in concert (or be even
unified).
