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Date: Thu, 24 Sep 2009 17:24:00 -0000
Subject: [Bug c/41462]  New: redundant instructions with long double returned value
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From: "yuri at tsoft dot com" <gcc-bugzilla@gcc.gnu.org>
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When I compile this function:
double f(long double i) {return (i);}
with gcc flags -S -O3, I get the assembly below.

There are two redundant FPU instructions there. double value is already in FPU
after fldt. No need to store it and load it back since difference between
double and long double is only in memory representation, and in FPU registers
they are the same.

---- asm output (relevant part) ----
f:
        pushl   %ebp
        movl    %esp, %ebp
        subl    $8, %esp   <---- redundant related stack adjustment
        fldt    8(%ebp)    
        fstpl   -8(%ebp)   <---- redundant STORE
        fldl    -8(%ebp)   <---- redundant LOAD
        leave
        ret


-- 
           Summary: redundant instructions with long double returned value
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: yuri at tsoft dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41462