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[Bug tree-optimization/60770] New: disappearing clobbers
- From: "glisse at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Sat, 05 Apr 2014 22:31:51 +0000
- Subject: [Bug tree-optimization/60770] New: disappearing clobbers
- Auto-submitted: auto-generated
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60770
Bug ID: 60770
Summary: disappearing clobbers
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: glisse at gcc dot gnu.org
Hello,
looking at Manuel's testcase from PR 60517, I notice that EINLINE changes:
D.2253 = A::getB (&a);
to:
D.2264 = a.b;
D.2263 = D.2264;
D.2253 = D.2263;
(several copies, but only the original D.2253 has a clobber)
and ESRA changes:
D.2253 = D.2263;
D.2253 ={v} {CLOBBER};
_5 = MEM[(double *)&D.2253];
to:
D.2253 = D.2263;
SR.1_3 = MEM[(struct B *)&D.2263];
D.2253 ={v} {CLOBBER};
_5 = SR.1_3;
The clobber then disappears in release_ssa.
It is correct, but not so helpful, because it hides the fact that we are
reading from dead memory. If I disable ESRA, the clobber and the memory read
are still present in the right order in the .optimized dump at -O3.
Would it be possible to keep the memory read after the clobber, without
affecting performance?
class B {
public:
double x[2];
};
class A {
B b;
public:
B getB(void) { return b; }
};
double foo(A a) {
double * x = &(a.getB().x[0]);
return x[0];
}