[Bug tree-optimization/83190] missing strlen optimization of the empty string
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83190 Andrew Pinski changed: What|Removed |Added Severity|normal |enhancement
[Bug tree-optimization/83190] missing strlen optimization of the empty string
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83190
Leslie Zhai changed:
What|Removed |Added
CC||lesliezhai at llvm dot org.cn
--- Comment #6 from Leslie Zhai ---
(In reply to Martin Sebor from comment #1)
> Clang emits optimal code for both functions.
Yep!
; ModuleID = 'a.c'
source_filename = "a.c"
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-redhat-linux"
; Function Attrs: norecurse nounwind readnone uwtable
define i32 @f() local_unnamed_addr #0 {
ret i32 0
}
; Function Attrs: norecurse nounwind readnone uwtable
define i32 @g() local_unnamed_addr #0 {
ret i32 0
}
attributes #0 = { norecurse nounwind readnone uwtable
"correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false"
"less-precise-fpmad"="false" "no-frame-pointer-elim"="false"
"no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false"
"no-signed-zeros-fp-math"="false" "no-trapping-math"="false"
"stack-protector-buffer-size"="8" "target-cpu"="x86-64"
"target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false"
"use-soft-float"="false" }
!llvm.module.flags = !{!0}
!llvm.ident = !{!1}
!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{!"LLVM China clang version 7.0.0 (g...@github.com:llvm-mirror/clang.git
87bcdaa7f2311f57c35c18efc6cbf5a973a67de7) (g...@github.com:llvm-mirror/llvm.git
4eeea16aaacd6134fd411abcdbab15b630f3302b) (based on LLVM 7.0.0svn)"}
[Bug tree-optimization/83190] missing strlen optimization of the empty string
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83190
Jakub Jelinek changed:
What|Removed |Added
CC||jakub at gcc dot gnu.org
--- Comment #5 from Jakub Jelinek ---
The strlen pass doesn't track of all the string lengths though, that would be
prohibitive, at least with the current infrastructure (say char a[100] =
{}; just notes that strlen(a) is 0, not that strlen(a + 253) is also 0.
Generally, the entry for such a pointer is only created when such pointer is
constructed, and at that point it is too late to find the length from the
earlier initializer.
[Bug tree-optimization/83190] missing strlen optimization of the empty string
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83190 Richard Biener changed: What|Removed |Added Status|UNCONFIRMED |NEW Last reconfirmed||2017-11-28 Ever confirmed|0 |1 --- Comment #4 from Richard Biener --- Confirmed. Probably some off-by-one error.
[Bug tree-optimization/83190] missing strlen optimization of the empty string
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83190
--- Comment #3 from Martin Sebor ---
sizeof "012\0" is 5. There are two NULs at the end, one explicit in the
initializer string and one implicitly appended by the compiler.
That the size is 5 can also be seen in the dump of g():
g ()
{
char a[5];
...
}
[Bug tree-optimization/83190] missing strlen optimization of the empty string
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83190 --- Comment #2 from Andrew Pinski --- Isn't the sizeof a, 4? If so the call to strlen in g is undefined.
[Bug tree-optimization/83190] missing strlen optimization of the empty string
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83190 Martin Sebor changed: What|Removed |Added Keywords||missed-optimization --- Comment #1 from Martin Sebor --- Clang emits optimal code for both functions.
