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Date: Wed, 21 Jul 2010 21:06:00 -0000
Subject: [Bug target/45026]  New: Empty function compiles to many loads and stores
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From: "steven at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
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Consider this test case:
typedef struct teststruct
{
  double d;
  char f1;
  int arr[15];
} teststruct;

void
copystruct5 (teststruct param)
{
  return;
}

The mighty copystruct5 function does absolutely nothing, so I expect this to be
compiled to absolutely nothing. But not so with r162374 at -O2:

        .file   "t.c"
        .pred.safe_across_calls p1-p5,p16-p63
        .text
        .align 16
        .align 64
        .global copystruct5#
        .type   copystruct5#, @function
        .proc copystruct5#
copystruct5:
        .prologue
        .spill 48
        .mmi
        .fframe 48
        adds r12 = -48, r12
[.L2:]  
        .body
        ;;
        mov r14 = r12
        adds r15 = 16, r12
        ;;
        .mmi
        st8 [r14] = r32, 8
        st8 [r15] = r34
        nop 0
        ;;
        .mmi
        st8 [r14] = r33
        nop 0
        adds r14 = 24, r12
        ;;
        .mmi
        st8 [r14] = r35
        nop 0
        adds r14 = 32, r12
        ;;
        .mmi
        st8 [r14] = r36
        nop 0
        adds r14 = 40, r12
        ;;
        .mmi
        st8 [r14] = r37
        nop 0
        adds r14 = 48, r12
        ;;
        .mmi
        st8 [r14] = r38
        nop 0
        adds r14 = 56, r12
        ;;
        .mib
        st8 [r14] = r39
        .restore sp
        adds r12 = 48, r12
        br.ret.sptk.many b0
        .endp copystruct5#
        .ident  "GCC: (GNU) 4.6.0 20100721 (experimental) [trunk revision
162374]"

What's that?!


-- 
           Summary: Empty function compiles to many loads and stores
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: steven at gcc dot gnu dot org
GCC target triplet: ia64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45026