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Subject: [Bug rtl-optimization/99596] [11 Regression] arm: internal error in
 single_pred_edge
Date: Fri, 16 Apr 2021 11:38:19 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99596

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Sandiford <rsandifo@gcc.gnu.o=
rg>:

https://gcc.gnu.org/g:b4d6af55fe55c0eab87ab875bfd0346677e12236

commit r11-8213-gb4d6af55fe55c0eab87ab875bfd0346677e12236
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Fri Apr 16 12:38:01 2021 +0100

    rtlanal: Don't assume that calls write to a global SP [PR99596]

    This patch is a GCC 11 regression caused by the rtl-ssa code.
    Normally we treat calls as containing a potential set of a global
    register, but DF makes a sensible exception for the stack pointer:

          if (i =3D=3D STACK_POINTER_REGNUM)
            /* The stack ptr is used (honorarily) by a CALL insn.  */
            df_ref_record (DF_REF_BASE, collection_rec, regno_reg_rtx[i],
                           NULL, bb, insn_info, DF_REF_REG_USE,
                           DF_REF_CALL_STACK_USAGE | flags);
          else if (global_regs[i])
            {
              /* Calls to const functions cannot access any global registers
and
                 calls to pure functions cannot set them.  All other calls =
may
                 reference any of the global registers, so they are recorde=
d as
                 used. */

    The only DF definition of SP was therefore the one in the entry block.
    However, the rtlanal.c rtx_properties code (wrongly) assumed that calls
    also clobbered the global SP.  This led to multiple definitions of SP
    when we only expected one.

    This patch tightens the rtlanal.c handling of global registers
    to match the DF approach.

    gcc/
            PR rtl-optimization/99596
            * rtlanal.c (rtx_properties::try_to_add_insn): Don't add global
            register accesses for const calls.  Assume that pure functions
            can only read from global registers.  Ignore cases in which
            the stack pointer has been marked global.

    gcc/testsuite/
            PR rtl-optimization/99596
            * gcc.target/arm/pr99596.c: New test.=