https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61583
Bug ID: 61583
Summary: stage2 and stage3 compare failure due to value range
loss
Product: gcc
Version: 4.9.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: bootstrap
Assignee: unassigned at gcc dot gnu.org
Reporter: amodra at gmail dot com
Seen first on ibm-4.9 branch with powerpc64, but also occurs on 4.9 branch with
both powerpc64 and x86_64. x86_64 configured with --enable-threads=posix
--disable-shared --disable-libmudflap --disable-libssp --disable-lto
--disable-libgomp --without-ppl --without-cloog --disable-checking
--enable-languages=c,c++
results for revision 211867 x86_64 as follows, powerpc64 doesn't hit the
builtins.o fail. Note that --disable-checking seems necessary.
Bootstrap comparison failure!
gcc/tree-vect-stmts.o differs
gcc/builtins.o differs
gcc/tree-vect-loop.o differs
Disassembling tree-vect-stmts.o shows loop exit branches differ for
for (j = 0; j < ncopies; ++j)
in vectorizable_mask_load_store.
ivopts details dump differences (- no debug, + debug):
@@ -16220,10 +19173,11 @@
Analyzing # of iterations of loop 1
exit condition [1, + , 1](no_overflow) < ncopies_19
- bounds on difference of bases: 0 ... 2147483646
+ bounds on difference of bases: -2147483649 ... 2147483646
result:
+ zero if ncopies_19 <= 0
# of iterations (unsigned int) ncopies_19 + 4294967295, bounded by
2147483646
- number of iterations (unsigned int) ncopies_19 + 4294967295
+ number of iterations (unsigned int) ncopies_19 + 4294967295; zero if
ncopies_19 <= 0
Induction variables:
@@ -16334,7 +19288,7 @@
0 0 0 1
1 0 0 1
2 0 0 1
- 3 0 0 1
+ 3 4 1 1
Use 2:
cand cost compl. depends on
@@ -16428,18 +19382,17 @@
base 0
step 1
-Replacing exit test: if (ncopies_19 > j_153)
bool vectorizable_assignment(gimple, gimple_stmt_iterator*,
gimple_statement_base**, slp_tree) (struct gimple_statement_base * stmt
{
[snip]
So there's why the exit test changes, with no debug output the exit test is
if (ncopies_19 != j_153), with debug info you keep the original test.
A gdb session shows that ncopies_19 has NULL SSA_NAME_RANGE_INFO during ivopts
with -g, but does have SSA_NAME_RANGE_INFO without -g, which agrees with the
dump output above.
