[Bug tree-optimization/19792] Missed optimizations due to signedness in the way
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19792 --- Comment #8 from Richard Biener --- I think for foo the "solution" is to only consider indices with well-defined behavior, that is, for size_lookup[] indices in [0,257] which means we should be safely able to truncate the index to unsigned char (for the purpose of analysis only!). Note we're not value-numbering (int) t the same as t but even size_lookup[(short) t] should result in the same value to be loaded unless undefined behavior is invoked. Of course extern unsigned char size_lookup[257]; might be considered extern unsigned char size_lookup[]; for QOI reasons and existing broken code, so... but just change the testcase to non-extern size_lookup. The solution might ly in value-numbering which could, when value-numbering the two loads lookup (and insert!) VNs of (shortest-allowed-type)index. The danger is of course that the shortest-allowed-type might differ depentent on the shape of the lookup where otherwise we'd compute the same VN. I'm quite sure we can't simply trust TYPE_DOMAIN of TREE_TYPE of TREE_OPERAND (array-ref, 0) when constraining operand 1.
[Bug tree-optimization/19792] Missed optimizations due to signedness in the way
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19792 Steven Bosscher changed: What|Removed |Added Last reconfirmed|2016-08-06 00:00:00 |2019-3-4 CC||rguenth at gcc dot gnu.org --- Comment #7 from Steven Bosscher --- Still an issue as of "g++ (Compiler-Explorer-Build) 9.0.1 20190303 (experimental)" on x86-64 at -O2: _Z3fooj: movslq %edi, %rax movl%edi, %edi movzbl size_lookup(%rdi), %edx cmpb%dl, size_lookup(%rax) sete%al movzbl %al, %eax ret _Z3barj: movl$1, %eax ret FWIW "clang version 7.0.0 (tags/RELEASE_700/final 342594)" at -O2: _Z3fooj:# @_Z3fooj movslq %edi, %rax movbsize_lookup(%rax), %cl movl%eax, %edx xorl%eax, %eax cmpbsize_lookup(%rdx), %cl sete%al retq _Z3barj:# @_Z3barj movl$1, %eax retq and "icc (ICC) 19.0.1.144 20181018": _Z3fooj: xorl %eax, %eax#6.36 movslq%edi, %rdi#6.11 movb size_lookup(%rdi), %dl#6.11 movl %edi, %edi#6.36 cmpb size_lookup(%rdi), %dl#6.36 sete %al #6.36 ret #6.36 _Z3barj: movl $1, %eax #13.15 ret
[Bug tree-optimization/19792] Missed optimizations due to signedness in the way
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19792 Bug 19792 depends on bug 15459, which changed state. Bug 15459 Summary: [meta-bug] there should be a tree combiner like the rtl one https://gcc.gnu.org/bugzilla/show_bug.cgi?id=15459 What|Removed |Added Status|ASSIGNED|RESOLVED Resolution|--- |FIXED
[Bug tree-optimization/19792] Missed optimizations due to signedness in the way
--- Comment #6 from pinskia at gcc dot gnu dot org 2006-05-05 09:17 --- the issue for foo might be considered a different harder issue to resolve. I think we need to decide what type is the argument for the ARRAY_REF, is it the type which the ARRAY has for its bounds or some other type? -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19792
[Bug tree-optimization/19792] Missed optimizations due to signedness in the way
--- Comment #4 from rguenth at gcc dot gnu dot org 2006-05-04 13:57 --- Subject: Bug 19792 Author: rguenth Date: Thu May 4 13:56:52 2006 New Revision: 113527 URL: http://gcc.gnu.org/viewcvs?root=gccview=revrev=113527 Log: 2006-05-04 Richard Guenther [EMAIL PROTECTED] PR tree-optimization/14287 PR tree-optimization/14844 PR tree-optimization/19792 PR tree-optimization/21608 PR tree-optimization/27090 * tree-ssa-pre.c (try_combine_conversion): New function. (compute_avail): After constructing the value-handle expression, use try_combine_conversion to combine NOP_EXPRs with previous value-handle expressions and use the result if it is available. * gcc.dg/tree-ssa/ssa-fre-1.c: New testcase. * gcc.dg/tree-ssa/ssa-fre-2.c: Likewise. * gcc.dg/tree-ssa/ssa-fre-3.c: Likewise. * gcc.dg/tree-ssa/ssa-fre-4.c: Likewise. * gcc.dg/tree-ssa/ssa-fre-5.c: Likewise. Added: trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-1.c trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-2.c trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-3.c trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-4.c trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-5.c Modified: trunk/gcc/ChangeLog trunk/gcc/testsuite/ChangeLog trunk/gcc/tree-ssa-pre.c -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19792
[Bug tree-optimization/19792] Missed optimizations due to signedness in the way
--- Comment #5 from rguenth at gcc dot gnu dot org 2006-05-04 15:04 ---
bar is now fixed.
;; Function foo (foo)
Analyzing Edge Insertions.
foo (t)
{
bb 2:
return size_lookup[(int) t] == size_lookup[t];
}
;; Function bar (bar)
Analyzing Edge Insertions.
bar (t)
{
bb 2:
return 1;
}
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19792
[Bug tree-optimization/19792] Missed optimizations due to signedness in the way
--- Additional Comments From kazu at cs dot umass dot edu 2005-03-16 14:59
---
FYI, here is the tailc dump that I get with the current mainline.
;; Function foo (foo)
foo (t)
{
unsigned char D.1137;
unsigned int t.1;
unsigned char D.1135;
int t.0;
int D.1133;
bb 0:
t.0_2 = (int) t_1;
D.1135_4 = size_lookup[t.0_2];
D.1137_6 = size_lookup[t_1];
D.1133_7 = D.1135_4 == D.1137_6;
return D.1133_7;
}
;; Function bar (bar)
bar (t)
{
int a;
unsigned int a.2;
int D.1142;
bb 0:
a_2 = (int) t_1;
a.2_3 = (unsigned int) a_2;
D.1142_4 = t_1 == a.2_3;
return D.1142_4;
}
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19792
[Bug tree-optimization/19792] Missed optimizations due to signedness in the way
--- Additional Comments From kazu at cs dot umass dot edu 2005-02-13 14:17 --- The testcase in this PR was reduced from ggc-page.c:ggc_alloc_typed_stat. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19792
[Bug tree-optimization/19792] Missed optimizations due to signedness in the way
-- What|Removed |Added CC||stevenb at suse dot de http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19792
[Bug tree-optimization/19792] Missed optimizations due to signedness in the way
-- What|Removed |Added OtherBugsDependingO||19721 nThis|| http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19792
[Bug tree-optimization/19792] Missed optimizations due to signedness in the way
--- Additional Comments From pinskia at gcc dot gnu dot org 2005-02-06 16:17 --- Confirmed, For bar, my tree combiner fixes the missed optimization. Not for foo. -- What|Removed |Added BugsThisDependsOn||15459 Status|UNCONFIRMED |NEW Ever Confirmed||1 Last reconfirmed|-00-00 00:00:00 |2005-02-06 16:17:02 date|| http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19792
