https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91579
Bug ID: 91579
Summary: tailr1 pass creates redundant phi nodes
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: jamborm at gcc dot gnu.org
Target Milestone: ---
Host: x86_64-linux
Target: x86_64-linux
When compiling the following testcase (at least at -O2 and higher),
the early tail-call pass creates redundant PHI nodes. The problem
with them is that ipa-prop then cannot see through them and does not
discover that an unchanged scalar argument is passed to another call.
As a consequence we lose information in jump functions and may not
clone the function when we should.
typedef long unsigned int size_t;
typedef int (*compare_t)(const void *, const void *);
int partition (void *base, size_t nmemb, size_t size, compare_t cmp);
void
my_qsort (void *base, size_t nmemb, size_t size, compare_t cmp)
{
int pt;
if (nmemb > 1)
{
pt = partition (base, nmemb, size, cmp);
my_qsort (base, pt + 1, size, cmp);
my_qsort ((void*)((char*) base + (pt + 1) * size),
nmemb - pt - 1, size, cmp);
}
}
Results into:
<bb 2> :
# base_13 = PHI <base_6(D)(0), _9(3)>
# nmemb_11 = PHI <nmemb_7(D)(0), _5(3)>
# size_14 = PHI <size_20(D)(0), size_14(3)>
# cmp_15 = PHI <cmp_21(D)(0), cmp_15(3)>
where the last two PHI nodes are superfluous.
(I think I have a patch to address it, let me test it.)
