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From: "schwab@linux-m68k.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/97682] New: Miscompiled tail call with -fPIC
Date: Mon, 02 Nov 2020 21:53:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97682

            Bug ID: 97682
           Summary: Miscompiled tail call with -fPIC
           Product: gcc
           Version: 10.2.1
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: schwab@linux-m68k.org
  Target Milestone: ---
            Target: riscv64-*-*

Created attachment 49488
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D49488&action=3Dedit
BlockFrequencyInfo.ii

When the attached file is compiled with -fPIC -O3, the tail call to
std::vector<llvm::BlockFrequencyInfoImplBase::FrequencyData,
std::allocator<llvm::BlockFrequencyInfoImplBase::FrequencyData>
>::_M_default_append(unsigned long) is missing in
llvm::BlockFrequencyInfoImpl<llvm::BasicBlock>::initializeRPOT():

.L2924:
        li      t1,4096         #,
        add     sp,sp,t1        #,,
        ld      ra,376(sp)              #,
        ld      s0,368(sp)              #,
        ld      s1,360(sp)              #,
        ld      s3,344(sp)              #,
        ld      s4,336(sp)              #,
        ld      s5,328(sp)              #,
        ld      s6,320(sp)              #,
        ld      s7,312(sp)              #,
        ld      s8,304(sp)              #,
        ld      s9,296(sp)              #,
        ld      s10,288(sp)             #,
        ld      s11,280(sp)             #,
# /usr/include/c++/10/bits/stl_vector.h:940:      _M_default_append(__new_s=
ize
- size());
        addi    a0,s2,8 #,, this
        ld      s2,352(sp)              #,
# /usr/include/c++/10/bits/stl_vector.h:940:      _M_default_append(__new_s=
ize
- size());
        sub     a1,a5,a1        #, _680, tmp1548
        addi    sp,sp,384       #,,
# /usr/include/c++/10/bits/stl_vector.h:940:      _M_default_append(__new_s=
ize
- size());
        jr      t1              #

Without -fPIC, the last line has the correct tail call:

        tail=20=20=20
_ZNSt6vectorIN4llvm26BlockFrequencyInfoImplBase13FrequencyDataESaIS2_EE17_M=
_default_appendEm
           #=