Bandhav Veluri via llvm-dev
2020-Jun-28 08:18 UTC
[llvm-dev] __restirct ignored when including headers like <cmath>
Hi,
I am observing a strange behaviour in which Clang ignores __restirct when I
include some standard headers.
For example, this code:
void vec_add(int* __restrict a,
int* __restrict b,
int n) {
#pragma unroll 4
for(int i=0; i<n; ++i) {
a[i] += b[i];
}
}
results in:
; Function Attrs: nofree norecurse nounwind
define dso_local void @_Z7vec_addPiS_i(i32* noalias nocapture %a, i32*
noalias nocapture readonly %b, i32 %n) local_unnam
ed_addr #0 {
entry:
.
.
...
(note the noaliass before function arguments).
But this code:
#include <cmath>
void vec_add(int* __restrict a,
int* __restrict b,
int n) {
#pragma unroll 4
for(int i=0; i<n; ++i) {
a[i] += b[i];
}
}
results in:
; Function Attrs: nofree norecurse nounwind
define dso_local void @_Z7vec_addPiS_i(i32* nocapture %a, i32* nocapture
readonly %b, i32 %n) local_unnamed_addr #0 {
entry:
%cmp6 = icmp sgt i32 %n, 0
br i1 %cmp6, label %for.body.preheader, label %for.cond.cleanup
.
.
...
I'm running this with LLVM RISC-V backend using RISC-V GCC compiled Newlib
as the C/C++ library.
Is it not okay to use GCC libraries with LLVM? Or could this be a specific
issue with Newlib's header files misinterpreted by Clang?
Thank you,
Bandhav
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Bandhav Veluri via llvm-dev
2020-Jun-29 16:51 UTC
[llvm-dev] __restirct ignored when including headers like <cmath>
Hi, Later found out this is because some Newlib headers defined __restrict as empty. __restrict__ seems to work... What's the supposed difference between __restrict and __restrict__? Thanks, Bandhav On Sun, Jun 28, 2020 at 1:18 AM Bandhav Veluri <bandhav.veluri00 at gmail.com> wrote:> Hi, > > I am observing a strange behaviour in which Clang ignores __restirct when > I include some standard headers. > > For example, this code: > void vec_add(int* __restrict a, > int* __restrict b, > int n) { > #pragma unroll 4 > for(int i=0; i<n; ++i) { > a[i] += b[i]; > } > } > > results in: > ; Function Attrs: nofree norecurse nounwind > define dso_local void @_Z7vec_addPiS_i(i32* noalias nocapture %a, i32* > noalias nocapture readonly %b, i32 %n) local_unnam > ed_addr #0 { > entry: > . > . > ... > (note the noaliass before function arguments). > > But this code: > #include <cmath> > > void vec_add(int* __restrict a, > int* __restrict b, > int n) { > #pragma unroll 4 > for(int i=0; i<n; ++i) { > a[i] += b[i]; > } > } > > results in: > ; Function Attrs: nofree norecurse nounwind > define dso_local void @_Z7vec_addPiS_i(i32* nocapture %a, i32* nocapture > readonly %b, i32 %n) local_unnamed_addr #0 { > entry: > %cmp6 = icmp sgt i32 %n, 0 > br i1 %cmp6, label %for.body.preheader, label %for.cond.cleanup > . > . > ... > > I'm running this with LLVM RISC-V backend using RISC-V GCC compiled Newlib > as the C/C++ library. > > Is it not okay to use GCC libraries with LLVM? Or could this be a specific > issue with Newlib's header files misinterpreted by Clang? > > Thank you, > Bandhav >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20200629/9809c9a6/attachment-0001.html>
Johannes Doerfert via llvm-dev
2020-Jun-29 22:56 UTC
[llvm-dev] __restirct ignored when including headers like <cmath>
From wikipedia (https://en.wikipedia.org/wiki/Restrict) C++ <https://en.wikipedia.org/wiki/C%2B%2B> does not have standard support for |restrict|, but many compilers have equivalents that usually work in both C++ and C, such as the GCC <https://en.wikipedia.org/wiki/GNU_Compiler_Collection>'s and Clang <https://en.wikipedia.org/wiki/Clang>'s |__restrict__|, and Visual C++ <https://en.wikipedia.org/wiki/Visual_C%2B%2B>'s |__declspec(restrict)|. In addition, |__restrict| is supported by those three compilers. The exact interpretation of these alternative keywords vary by the compiler: Hope this helps, ~ Johannes On 6/29/20 11:51 AM, Bandhav Veluri via llvm-dev wrote:> Hi, > > Later found out this is because some Newlib headers defined __restrict as > empty. __restrict__ seems to work... > > What's the supposed difference between __restrict and __restrict__? > > Thanks, > Bandhav > > On Sun, Jun 28, 2020 at 1:18 AM Bandhav Veluri <bandhav.veluri00 at gmail.com> > wrote: > >> Hi, >> >> I am observing a strange behaviour in which Clang ignores __restirct when >> I include some standard headers. >> >> For example, this code: >> void vec_add(int* __restrict a, >> int* __restrict b, >> int n) { >> #pragma unroll 4 >> for(int i=0; i<n; ++i) { >> a[i] += b[i]; >> } >> } >> >> results in: >> ; Function Attrs: nofree norecurse nounwind >> define dso_local void @_Z7vec_addPiS_i(i32* noalias nocapture %a, i32* >> noalias nocapture readonly %b, i32 %n) local_unnam >> ed_addr #0 { >> entry: >> . >> . >> ... >> (note the noaliass before function arguments). >> >> But this code: >> #include <cmath> >> >> void vec_add(int* __restrict a, >> int* __restrict b, >> int n) { >> #pragma unroll 4 >> for(int i=0; i<n; ++i) { >> a[i] += b[i]; >> } >> } >> >> results in: >> ; Function Attrs: nofree norecurse nounwind >> define dso_local void @_Z7vec_addPiS_i(i32* nocapture %a, i32* nocapture >> readonly %b, i32 %n) local_unnamed_addr #0 { >> entry: >> %cmp6 = icmp sgt i32 %n, 0 >> br i1 %cmp6, label %for.body.preheader, label %for.cond.cleanup >> . >> . >> ... >> >> I'm running this with LLVM RISC-V backend using RISC-V GCC compiled Newlib >> as the C/C++ library. >> >> Is it not okay to use GCC libraries with LLVM? Or could this be a specific >> issue with Newlib's header files misinterpreted by Clang? >> >> Thank you, >> Bandhav >> > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20200629/ee04cfe6/attachment.html>