The following code:
---------------------------------------------
extern void bar (double);
void foo (void) { bar (0.0); }
---------------------------------------------
used to produce a tail call with GCC 3.3.3 (SuSE Linux):
---------------------------------------------
.text
.p2align 4,,15
.globl foo
.type foo, @function
foo:
.LFB3:
xorpd %xmm0, %xmm0
jmp bar
.LFE3:
.size foo, .-foo
---------------------------------------------
GCC 4.0 20050124 produces a real call instead:
---------------------------------------------
.text
.p2align 4,,15
.globl foo
.type foo, @function
foo:
.LFB2:
xorpd %xmm0, %xmm0
subq $8, %rsp
.LCFI0:
call bar
addq $8, %rsp
ret
.LFE2:
.size foo, .-foo
---------------------------------------------
The problem appears to be in expanding from trees to RTL because the
call is properly marked as being in a tail position:
;; Function foo (foo)
Analyzing Edge Insertions.
foo ()
{
<bb 0>:
bar (0.0) [tail call];
return;
}
This happens for less trivial functions also, and can be a pretty
severe code pessimization.
--
Summary: [4.0 regression] missed tail call
Product: gcc
Version: 4.0.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P1
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: steven at gcc dot gnu dot org
CC: gcc-bugs at gcc dot gnu dot org,hubicka at gcc dot gnu
dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19616
