[Bug target/19616] New: [4.0 regression] missed tail call

[steven at gcc dot gnu dot org]

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