[patch] Fix ICE on ACATS test for Aarch64 at -O

[Eric Botcazou <ebotcazou@adacore.com>]

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Hi,

for the attached reduced testcase, the ICE is:

eric@polaris:~/gnat/bugs/P901-028> ~/build/gcc/aarch64-linux/gcc/gnat1 -quiet 
p.adb -O -I ~/build/gcc/aarch64-linux/gcc/ada/rts
+===========================GNAT BUG DETECTED==============================+
| 7.0.0 20160914 (experimental) [trunk revision 240142] (aarch64-linux) GCC 
error:|
| in expand_shift_1, at expmed.c:2451                                      |
| Error detected around p.adb:21:29

#0  internal_error (gmsgid=0x22327b7 "in %s, at %s:%d")
    at /home/eric/svn/gcc/gcc/diagnostic.c:1347
#1  0x0000000001e2373b in fancy_abort (
    file=0x1f965f8 "/home/eric/svn/gcc/gcc/expmed.c", line=2451, 
    function=0x1f96ce7 <expand_shift_1(tree_code, machine_mode, rtx_def*, 
rtx_def*, rtx_def*, int)::__FUNCTION__> "expand_shift_1")
    at /home/eric/svn/gcc/gcc/diagnostic.c:1415
#2  0x0000000000eb435c in expand_shift_1 (code=RSHIFT_EXPR, mode=OImode, 
    shifted=0x7ffff68e02e8, amount=0x7ffff68bcef0, target=0x0, unsignedp=1)
    at /home/eric/svn/gcc/gcc/expmed.c:2451
#3  0x0000000000eb43bd in expand_shift (code=RSHIFT_EXPR, mode=OImode, 
    shifted=0x7ffff68e02e8, amount=255, target=0x0, unsignedp=1)
    at /home/eric/svn/gcc/gcc/expmed.c:2467
#4  0x0000000000ebefe3 in emit_store_flag (target=0x7ffff68de780, code=NE, 
    op0=0x7ffff68de798, op1=0x7ffff6c3d400, mode=OImode, unsignedp=1, 
    normalizep=1) at /home/eric/svn/gcc/gcc/expmed.c:5826
#5  0x0000000000ebe979 in emit_store_flag (target=0x7ffff68de780, code=NE, 
    op0=0x7ffff68dc138, op1=0x7ffff68dc030, mode=OImode, unsignedp=1, 
    normalizep=1) at /home/eric/svn/gcc/gcc/expmed.c:5670
#6  0x0000000000ebf0ab in emit_store_flag_force (target=0x7ffff68de780, 
    code=NE, op0=0x7ffff68dc138, op1=0x7ffff68dc030, mode=OImode, unsignedp=1, 
    normalizep=1) at /home/eric/svn/gcc/gcc/expmed.c:5860
#7  0x0000000000ef0aba in do_store_flag (ops=0x7fffffffd4d0, 
    target=0x7ffff68de780, mode=QImode) at /home/eric/svn/gcc/gcc/expr.c:11408
#8  0x0000000000ee6873 in expand_expr_real_2 (ops=0x7fffffffd4d0, target=0x0, 
    tmode=QImode, modifier=EXPAND_NORMAL) at 
/home/eric/svn/gcc/gcc/expr.c:9196

It's an attempt at generating a store-flag sequence with OImode and it fails 
because there are no shift operations supported in that mode.  It turns out 
that emit_store_flag_force knows how to fall back on a branchy sequence in 
that case so the attached patch simply removes the assertion.

Tested on x86-64/Linux, OK for the mainline?


2016-09-16  Eric Botcazou  <ebotcazou@adacore.com>

	* expmed.c (expand_shift_1): Remove assertion and adjust comment.
	(expand_shift): Adjust comment.

-- 
Eric Botcazou

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Index: expmed.c
===================================================================
--- expmed.c	(revision 240142)
+++ expmed.c	(working copy)
@@ -2247,7 +2247,7 @@ expand_dec (rtx target, rtx dec)
    and AMOUNT the rtx for the amount to shift by.
    Store the result in the rtx TARGET, if that is convenient.
    If UNSIGNEDP is nonzero, do a logical shift; otherwise, arithmetic.
-   Return the rtx for where the value is.  */
+   Return the rtx for where the value is or 0 if that cannot be done.  */
 
 static rtx
 expand_shift_1 (enum tree_code code, machine_mode mode, rtx shifted,
@@ -2448,7 +2448,6 @@ expand_shift_1 (enum tree_code code, mac
 	 define_expand for lshrsi3 was added to vax.md.  */
     }
 
-  gcc_assert (temp);
   return temp;
 }
 
@@ -2457,7 +2456,7 @@ expand_shift_1 (enum tree_code code, mac
    and AMOUNT the amount to shift by.
    Store the result in the rtx TARGET, if that is convenient.
    If UNSIGNEDP is nonzero, do a logical shift; otherwise, arithmetic.
-   Return the rtx for where the value is.  */
+   Return the rtx for where the value is, or 0 if that cannot be done.  */
 
 rtx
 expand_shift (enum tree_code code, machine_mode mode, rtx shifted,