similar to: How to let LLVM handle undefined behavior more gracefully?

Yes, thought of UBSan. But in our case, the target program runs on baremetal. It has very tight code size restriction and it has no stderr. Since LLVM already caught the behavior during compilation, it should notify users about it. On 2016-03-16 18:29, Mehdi Amini wrote: >> On Mar 16, 2016, at 6:16 PM, Zhao, Weiming via llvm-dev >> <llvm-dev at lists.llvm.org> wrote: >>

Yes, what I mean is a target independent node in the ISD::NodeType enum. I already did the node transformation DAGCombiner and target-specific lowering in the first place. It worked. But introducing a specific node will make the logic more clear. For example, in ARM, FDIV is a scalar operation. So, after DAGCombiner and Vector Type legalize, vectorized FDIV has been expanded into scalar versions,

In the section about poison values, the LLVM language reference manual says: "Values other than phi nodes depend on their operands." This implies that a select instruction's output can be poisoned by its not-selected argument value. If select were poisoned only by its selected argument, we would expect this fact to be mentioned specifically, as it is for phi. Next I'll

(+correct cfe-dev list) On Tue, Jan 12, 2016 at 2:57 PM, Alexey Samsonov <vonosmas at gmail.com> wrote: > Hi Yuri, > > On Mon, Jan 11, 2016 at 9:53 AM, Yury Gribov via llvm-dev < > llvm-dev at lists.llvm.org> wrote: > >> Hi all, >> >> UndefinedBehaviorSanitizer currently does not check for undefined >> behaviors which result from improper usage

--- On Thu, 9/20/12, Jim Grosbach <grosbach at apple.com> wrote: From: Jim Grosbach <grosbach at apple.com> Subject: Re: [LLVMdev] Proposal: New DAG node type for reciprocal operation To: "Weiming Zhao" <weimingz at codeaurora.org> Cc: llvmdev at cs.uiuc.edu Date: Thursday, September 20, 2012, 3:32 PM Sounds like a reasonable fit for a target-specific DAG combine. I

This weekend, I got an email from Nuno Lopes informing me that UBSAN now paid attention to attribute(nonnull), and he was having some problems with it going off when using libc++. I did some investigation, and found that he was exactly right - there were places (deep inside the vector code, for example) which called std::memcpy(null, null, 0) - which is definitely UB. In an ideal world, our C

Sanjoy, You have changed the subject. We still need real world examples showing how taking advantage of “undef” results in beneficial optimization. My belief is that they don’t exist, my reasoning is this: real world programmers are likely to run UBSan before compiling (or if they don’t they should), therefore it is highly unlikely that any “undef” will actually exist during

Dave, The way I see it there should be just one pass that implements deleting UB (maybe it would come to be called UBCE), and that one pass should have a command line option simply for the reason than all passes should have one. Peter Lawrence. > On Jul 26, 2017, at 10:02 PM, David Blaikie <dblaikie at gmail.com> wrote: > > > > On Wed, Jul 26, 2017 at 9:23 PM

David, -fsanitize=undefined sounds great, but is not quite what I want. I recently ran into a problem with "CodeGen/MachineSink.cpp” [*], for a target that has to expand Select into control flow. The original IR had two select in a row that were based on the same condition, so the CMP that sets the FLAGS reg in the second select was MCSE’ed to the earlier CMP in the first

Hi, When I’m compiling a code with –fvisibility=hidden –fPIC for ARM, I find that LLVM generates less optimized code than GCC. For example: test.cpp: void init(void *); int g0[100]; int g1[100]; int g2[100]; void foo() { init(&g0); init(&g1); init(&g2); } Clang will emit 1 GOT entry for each GV and 2 instructions to get the address: ldr

Sounds like a reasonable fit for a target-specific DAG combine. I suspect a target specific node wouldn't be necessary and the patterns could be matched directly. -Jim On Sep 20, 2012, at 3:26 PM, Weiming Zhao <weimingz at codeaurora.org> wrote: > Hi, > > In relaxed/fast math mode, if we can convert a/b to a * (1/b), we may get more performance when (1) “b” is loop

Yes, it's a bug. Please review https://reviews.llvm.org/D31716 On 4/5/2017 3:50 AM, Renato Golin wrote: > On 21 March 2017 at 18:32, Peter Jakubek via llvm-dev > <llvm-dev at lists.llvm.org> wrote: >> I think the current implementation for the call "bl __aeabi_idiv0" in >> builtins\arm\udivsi3.S is broken. >> At least for the case that __aeabi_idiv0

Hi, For the following code: void foo (); int main () {foo();} llvm emits "bl foo" Then I set foo at a far address in linking: aarch64-linux-gnu-gcc -Wl,--defsym=foo=0x80000000 a.o -o a.exe I got an error from ld: a.c:(.text+0x8): relocation truncated to fit: R_AARCH64_CALL26 against symbol `foo' define in *ABS* section in a.exe The question is: do I

Dave, Dead code elimination is generally done in a pass called dead code elimination, Can you give concrete examples why the same would not be true for UB code elimination ? Yes, speculatively hoisting code requires it to be UB-free, but that has nothing to do with UBCE deleting entire blocks of code because of the existence of UB. The former requires an analysis proving UB-absense, the

Hi all, UndefinedBehaviorSanitizer currently does not check for undefined behaviors which result from improper usage of standard library functions. One notorious instance of such errors is invalid usage of qsort or bsearch routines (or std::sort and friends in case of C++): * using comparison function that violates ordering axioms (reflexivity, symmetry, transitivity) * returning unstable

Hi Rafael, Yes, merging gv prevents linker to do garbage collection. Should it be implemented as a peephole pass? If we do it too early, the distance between GVs are not fixed yet. PS: Below is the GCC output with "extern" hidden: ldr r2, .L2 stmfd sp!, {r3, lr} .save {r3, lr} .LPIC0: add r0, pc, r2 bl _Z4initPv(PLT) ldr r1, .L2+4 .LPIC1: add r0, pc, r1 bl _Z4initPv(PLT) ldr

Mehdi, Hal’s transformation only kicks in in the *presence* of UB, and it does not matter how that UB got there, whether by function inlining or without function inlining. The problem with Hal’s argument is that the compiler does not have a built in ouija board with which it can conjure up the spirit of the author of the source code and find out if the UB was intentional with the

Hi, In relaxed/fast math mode, if we can convert a/b to a * (1/b), we may get more performance when (1) "b" is loop invariant or (2) arch has faster reciprocal instruction (e.g. recipe/recips on ARM) or (3) arch has no vector div, but has vector mul and recip. So ,with this node type, a div node can be converted to a mul and a recip when desired. Then, each arch can further

On 01/13/2016 03:10 AM, Kostya Serebryany wrote: > FTR, here is one way to implement this in the library: > https://gcc.gnu.org/svn/gcc/branches/google/gcc-4_9/libstdc++-v3/include/bits/stl_algo.h > Search for "check sort predicate for strict weak ordering" Nice, although this wouldn't catch violations of transitivity (which is probably the most important type of bug).

On Mon, Jul 31, 2017 at 7:40 AM Peter Lawrence <peterl95124 at sbcglobal.net> wrote: > Dave, > Dead code elimination is generally done in a pass called dead > code elimination, > Can you give concrete examples why the same would not be true for UB code > elimination ? > I haven't actually looked at how optimizations on the basis of the code being UB-free