[Bug target/98694] [11 Regression] GCC produces incorrect code for loops with -O3 for skylake-avx512 and icelake-server

[crazylht at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98694

--- Comment #3 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Hongtao.liu from comment #1)
> cprop hardreg change
> 
> (insn 457 499 460 33 (set (reg:SI 39 r11 [orig:86 _11 ] [86])
>         (reg:SI 37 r9 [orig:86 _11 ] [86])) "test.c":29:36 75
> {*movsi_internal}
>      (expr_list:REG_DEAD (reg:SI 37 r9 [orig:86 _11 ] [86])
>         (nil)))
> 
> to
> 
> (insn 457 499 460 33 (set (reg:SI 39 r11 [orig:86 _11 ] [86])
>         (reg:SI 22 xmm2 [orig:86 _11 ] [86])) "test.c":29:36 75
> {*movsi_internal}
>      (expr_list:REG_DEAD (reg:SI 22 xmm2 [orig:86 _11 ] [86])
>         (nil)))
> 
> since it thought the lower 32bit of r9 and xmm2 is the same?
> 
> but with xmm2 defined as
> 
> 	kmovw	%k0, %edi	# 69	[c=4 l=4]  *movhi_internal/6
> 	kmovd	%k0, %edx	# 487	[c=4 l=3]  *movsi_internal/16
> 	vmovd	%edi, %xmm2	# 489
> 
> the bit16-32 is clear with kmovw(note k0 is equal to r9 with SImode, it's
> var_6 in source code)
> 
> (insn 69 68 70 12 (set (reg:HI 5 di [orig:96 _52 ] [96])
>         (reg:HI 68 k0 [orig:82 var_6.0_1 ] [82])) "test.c":21:23 76
> {*movhi_internal}
>      (nil))
> 
> (insn 489 75 78 12 (set (reg:SI 22 xmm2 [297])
>         (reg:SI 5 di [orig:96 _52 ] [96])) 75 {*movsi_internal}
>      (nil))

It seems to be be handled here.

cut from copy_value in regcprop.c:
----
  /* If SRC had been assigned a mode narrower than the copy, we can't
     link DEST into the chain, because not all of the pieces of the
     copy came from oldest_regno.  */
  else if (sn > hard_regno_nregs (sr, vd->e[sr].mode))
    return;
----

here we have %edi set as HImode, but use as SImode and be copied to %xmm2, but
the condition failed to check this beacuase both SImode and HImode has nregs as
1, since the upper part could be garbage, it can't link DEST into the chain.

        kmovw   %k0, %edi       # 69    [c=4 l=4]  *movhi_internal/6  <----HI
        kmovd   %k0, %edx       # 487   [c=4 l=3]  *movsi_internal/16 
        vmovd   %edi, %xmm2     # 489   [c=4 l=6]  *movsi_internal/13 <----SI
        sall    $16, %edx       # 73    [c=4 l=3]  *ashlsi3_1/0
        kmovw   %k0, %r8d       # 74    [c=4 l=5]  *zero_extendhisi2/1
        vpshuflw        $0, %xmm2, %xmm0        # 78    [c=4 l=5] 
*vec_dupv4hi/1
        orl     %edx, %r8d      # 75    [c=4 l=3]  *iorsi_1/0
        testw   %di, %di        # 82    [c=4 l=3]  *cmphi_ccno_1/0
        jle     .L52    # 83    [c=12 l=6]  *jcc
        kmovd   %k0, %r9d       # 85    [c=4 l=4]  *movsi_internal/16 <----SI
        testl   %r9d, %r9d      # 88    [c=4 l=3]  *cmpsi_ccno_1/0