search for: norecurse

Hi folks, I've been measuring some devirtualization statistics and I found that when barriers are introduced, the number of functions marked as norecurse is lower. The llvm.group.barrier is obviously norecursive and I've been thinking: is every intrinsic norecurse? I think it make sense to mark all of the intrinsics that can be considered as norecursive this way, so it won't gonna stop the optimizer marking functions as norecurse. Best Pio...

Hi, GlobalOpt may not consider demoting globals to locals in the "main" function when C is used. It used to consider "main" specifically prior to commit r253168 , for both C and C++. Since r253168, the check for the norecurse attribute may prevent "main" from being considered. This happens because the Function Attributes pass will not add the norecurse attribute to functions that have calls to library functions that aren't themselves marked with the norecurse attribute, such as putchar. Even a call to ll...

I think the conceptual issues have largely been sorted out, it is mostly that it is *much* harder to deduce norecurse than it might seem like superficially. On Mon, Mar 21, 2016 at 4:02 PM Mehdi Amini <mehdi.amini at apple.com> wrote: > On Mar 21, 2016, at 3:57 PM, Sanjin Sijaric via llvm-dev < > llvm-dev at lists.llvm.org> wrote: > > Hi, > > GlobalOpt may not consider demoting glob...

Hi Mehdi, You are right – modifying the Function Attributes pass to mark “main” as norecurse would break the C standard (unless it has a similar statement regarding “main” that the C++ standard has – I cannot find it), so that’s a no-go. Looks like there was an attempt to bypass library calls in the Function Attributes pass for the purpose of detecting norecurse functions: http://reviews....

Hi, Also, I think there is a bigger problem lurking than just with norecurse. I think that in general, functionattrs is not very good with attributes when intrinsics are present. E.g. https://bugs.llvm.org/show_bug.cgi?id=34696 Here dbg.value prevents both norecurse and readnone from being deduced. So, it would be nice to fix this for norecurse, but it would be even ni...

The test case that you added in this revision fails on several of the power buildbots (for example, http://lab.llvm.org:8011/builders/clang-ppc64-elf-linux2/builds/20127) and also when I build it locally: FAIL: Clang :: CodeGenCXX/main-norecurse.cpp (2951 of 27722) ******************** TEST 'Clang :: CodeGenCXX/main-norecurse.cpp' FAILED ******************** Script: -- /home/seurer/llvm/build/llvm-test/./bin/clang -cc1 -internal-isystem /home/seurer/llvm/build/llvm-test/bin/../lib/clang/3.8.0/include -nostdsysteminc -emit-llvm...

...ch didn't get a lot of attention, so probably others does not > consider it a huge deal. Anyway, if someone is willing to review this, I > can pursue rebasing it. Okay. We are interested in getting something akin to your patch delivered; at least so that the dbg intrinsics gets marked as norecurse. Unfortunately I'm not very familiar with more "esoteric" intrinsics, so I can't bring anything special to the table when it comes to reviewing that the set of exempted intrinsics is correct. Other than that I can gladly help in whatever way to help this patch land. (I rebased y...

> On 2015-Nov-05, at 08:31, Aaron Ballman <aaron at aaronballman.com> wrote: > > On Thu, Nov 5, 2015 at 11:26 AM, James Molloy <james at jamesmolloy.co.uk> wrote: >> Ah I see. >> >> I can't think of a way that would help users in any particular way offhand. >> I hadn't considered exposing it to clang users - do you think there is merit

...ould like to teach LLVM about its semantics. In particular, I would like LLVM to kill allocations that are "dead", similar to dead new in C++. Consider this example: ; ModuleID = '<stdin>' source_filename = "Module" ; Function Attrs: inaccessiblememonly noinline norecurse nounwind declare i8* @alloc(i64) local_unnamed_addr #0 ; Function Attrs: inaccessiblememonly noinline norecurse nounwind declare void @useClosure(i8*) local_unnamed_addr #1 ; Function Attrs: alwaysinline norecurse nounwind define void @main() #1 { entry: %closure.raw = tail call noalias i8* @al...

Hi, On my phone right now but I'll fish out the pertinent threads when I get to the office. Keyword searches for 'norecurse' on llvm-dev will probably get most of them. Indeed, this correctness improvement caused a performance regression on some programs. There is a way to revert to the old, broken behaviour: '-mllvm -force-attribute=main:norecurse'. Given how many people run old C code that rely on this pr...

[Adding llvm-dev and re-stating the situation for llvm-dev's benefit] *RFC: A new attribute, "norecurse".* In some cases, it is possible to demote global variables to local variables. This is possible when the global is only used in one function, and that function is known not to recurse (because if the function recurses, a local variable cannot be equivalent to a global as the global would hol...

...to many other attributes such as nocapture/nounwind, that are > > exposed to users and can be set by users in exceptional circumstances but > > are primarily inferred by the midend. > > Sorry, I was unclear. I meant to Clang users as a language-level > attribute (e.g., [[clang::norecurse]]), not LLVM users as an IR-level > attribute. > > ~Aaron > > > > > > James > > > > On Thu, 5 Nov 2015 at 16:03 Aaron Ballman <aaron at aaronballman.com> > wrote: > >> > >> On Thu, Nov 5, 2015 at 10:44 AM, James Molloy via llvm-dev &...

...Aaron Ballman <aaron at aaronballman.com> wrote: > On Thu, Nov 5, 2015 at 10:44 AM, James Molloy via llvm-dev > <llvm-dev at lists.llvm.org> wrote: > > [Adding llvm-dev and re-stating the situation for llvm-dev's benefit] > > > > RFC: A new attribute, "norecurse". > > > > In some cases, it is possible to demote global variables to local > variables. > > This is possible when the global is only used in one function, and that > > function is known not to recurse (because if the function recurses, a > local > > variabl...

...ntptr inbounds i8, i8* %2, i8 0 %4 = call [8 x i8] @12(i32 %1, i8* %3) [...] " test_opt.ll: " ; ModuleID = 'test_opt.bc' @__mla__system.1 = global i32 0 @0 = internal global [12 x i8] zeroinitializer @1 = internal unnamed_addr global [8 x i8] zeroinitializer ; Function Attrs: norecurse nounwind readnone define internal fastcc [8 x i8] @2() unnamed_addr #0 { ret [8 x i8] [i8 2, i8 0, i8 0, i8 0, i8 undef, i8 undef, i8 undef, i8 undef] } ; Function Attrs: norecurse nounwind define i32 @main() #1 { %1 = tail call fastcc [8 x i8] @2() store [8 x i8] %1, [8 x i8]* @1, align 1...

...as the value of @g isn't changed, but it is changed), and will cause function return wrong constant value '1', instead of '%n' (the correct value) , like following: **************************************************************************************** ; Function Attrs: nofree norecurse nounwind writeonly define i32 @bar(i32 %n) local_unnamed_addr #0 { entry: ret i32 1 } attributes #0 = { nofree norecurse nounwind writeonly } **************************************************************************************** And if remove the 'argmemonly' attribute, function @bar...

...; preds = %splittedblock21, %splittedblock19 ret void splittedblock15: ; preds = %splittedblock36 ret void splittedblock21: ; preds = %splittedblock38 %25 = xor i64 %6, %4 br label %splittedblock42 } ; Function Attrs: norecurse nounwind readnone define <2 x double> @func_3701811888700380719897139(...) local_unnamed_addr #1 { entry: ret <2 x double> <double 0xC00934F9D7726A00, double 0xFFCFDA8E9AFFB51D> } ; Function Attrs: norecurse noreturn nounwind readnone define { double, double } @func_00655594713...

...emit ir like: $cat a.ll --------------------------------------- ; ModuleID = 'a.c' source_filename = "a.c" target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128" target triple = "x86_64-unknown-linux-gnu" ; Function Attrs: norecurse nounwind readnone uwtable define dso_local float @foo(float %a, float %b) local_unnamed_addr #0 { entry: %add = fadd float %a, %b ret float %add } attributes #0 = { norecurse nounwind readnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls&...

...39;t changed, but it > is changed), and will cause function return wrong constant value '1', > instead of '%n' (the correct value) , like following: > **************************************************************************************** > > ; Function Attrs: nofree norecurse nounwind writeonly > define i32 @bar(i32 %n) local_unnamed_addr #0 { > entry: > ret i32 1 > } > > attributes #0 = { nofree norecurse nounwind writeonly } > **************************************************************************************** > > > And if remove th...

...viour 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*...

Hi: I am trying to implement interval arithmetic through llvm. I have a problem with the rounding mode with llvm.experimental.constrained.cos I have two pieces of codes: ; Function Attrs: norecurse nounwind readnone ssp uwtable define double @cosine_down(double returned) local_unnamed_addr #0 {   ; call the llvm intrinsic to perform downward cosine   %2 = call double @llvm.experimental.constrained.cos(double %0, metadata !"round.downward", metadata !"fpexcept.strict")   re...