PR111778, PowerPC: Do not depend on an undefined shift

I was building a cross compiler to PowerPC on my x86_86 workstation with the
latest version of GCC on October 11th.  I could not build the compiler on the
x86_64 system as it died in building libgcc.  I looked into it, and I
discovered the compiler was recursing until it ran out of stack space.  If I
build a native compiler with the same sources on a PowerPC system, it builds
fine.

I traced this down to a change made around October 10th:

| commit 8f1a70a4fbcc6441c70da60d4ef6db1e5635e18a (HEAD)
| Author: Jiufu Guo <guojiufu@linux.ibm.com>
| Date:   Tue Jan 10 20:52:33 2023 +0800
|
|   rs6000: build constant via li/lis;rldicl/rldicr
|
|   If a constant is possible left/right cleaned on a rotated value from
|   a negative value of "li/lis".  Then, using "li/lis ; rldicl/rldicr"
|   to build the constant.

The code was doing a -1 << 64 which is undefined behavior because different
machines produce different results.  On the x86_64 system, (-1 << 64) produces
-1 while on a PowerPC 64-bit system, (-1 << 64) produces 0.  The x86_64 then
recurses until the stack runs out of space.

If I apply this patch, the compiler builds fine on both x86_64 as a PowerPC
crosss compiler and on a native PowerPC system.

2023-10-12  Michael Meissner  <meissner@linux.ibm.com>

gcc/

	PR target/111778
	* config/rs6000/rs6000.cc (can_be_built_by_li_lis_and_rldicl): Protect
	code from shifts that are undefined.
	(can_be_built_by_li_lis_and_rldicr): Likewise.
	(can_be_built_by_li_and_rldic): Protect code from shifts that
	undefined.  Also replace uses of 1ULL with HOST_WIDE_INT_1U.

0 files changed, 0 insertions, 0 deletions