[Bug c++/34864] New: ldexp variants, folding

["tbptbp at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

Briefly: of all the ldexp variants only straight ldexp consistently get folded.
The overloaded c++ version, std::ldexp, is the easiest to derail, as this
testcase demonstrates (note: you can't get much more than 1 such call folded);
but it has also happened to me with ldexpf, it's just harder to trigger.

$ cat pr-ldexp.cc
#include <cmath>
#define L1(x) ldexp((float)(x | (1<<23)), -23)
#define L2(x) std::ldexp((float)(x | (1<<23)), -23)
int main(int argc, char *argv[]) {
        const float tbl[] = { L(0), L(1), L(2), L(3) };
        return int(tbl[argc]);
}
$ /usr/local/gcc-4.3-20080104/bin/g++ -O2 -march=k8 -DL=L1 pr-ldexp.cc -o pr1
$ /usr/local/gcc-4.3-20080104/bin/g++ -O2 -march=k8 -DL=L2 pr-ldexp.cc -o pr2

pr1:
 401091:       f3 0f 10 04 9d 00 20    movss  0x402000(,%ebx,4),%xmm0
 40109e:       f3 0f 2c c0             cvttss2si %xmm0,%eax
 4010a2:       c9                      leave

pr2:
 401090:       c7 45 e8 00 00 80 3f    movl   $0x3f800000,0xffffffe8(%ebp)
 401097:       c7 45 ec 01 00 80 3f    movl   $0x3f800001,0xffffffec(%ebp)
 40109e:       c7 45 f0 02 00 80 3f    movl   $0x3f800002,0xfffffff0(%ebp)
 4010a5:       c7 45 f4 03 00 80 3f    movl   $0x3f800003,0xfffffff4(%ebp)
 4010ac:       f3 0f 10 44 9d e8       movss  0xffffffe8(%ebp,%ebx,4),%xmm0
 4010b2:       8b 5d fc                mov    0xfffffffc(%ebp),%ebx
 4010b5:       f3 0f 2c c0             cvttss2si %xmm0,%eax
 4010b9:       c9                      leave 
(k8/sse codegen selected for clarity)


-- 
           Summary: ldexp variants, folding
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: tbptbp at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34864