similar to: [LLVMdev] Alias Analysis across functions

Hello All, I have met one may-alias case from llvm's alias analysis. The code snippet is as following: char buf[4]; void test (int idx) { char *a = &buf[3 - idx]; char *b = &buf[idx]; *a = 1; *b = 2; } I can see below output from alias set tracker for above code snippet. Alias sets for function 'test': Alias Set Tracker: 1 alias sets for 2 pointer values.  

Hi, LLVM community: I found basicaa seems not to tell must-not-alias for __restrict__ arguments in c/c++. It only compares two pointers and the underlying objects they point to. I wonder how clang does alias analysis for c/c++ keyword restrict. let assume we compile the following code: $cat myalias.cc float foo(float * __restrict__ v0, float * __restrict__ v1, float * __restrict__ v2, float *

Hi, Your problem is that the function arguments, which are makes as noalias, are not being directly used as the base objects of the array accesses: > %v0.addr = alloca float*, align 8 > %v1.addr = alloca float*, align 8 > %v2.addr = alloca float*, align 8 > %t.addr = alloca float*, align 8 ... > store float* %v0, float** %v0.addr, align 8 > store float* %v1, float** %v1.addr,

Hi , The following loop fails to be vectorized since the load c[i] is casted as i64 and the store c[i] is double. The loop access analysis gives up since they are in different types. Since these two memory operations are in the same size, I believe the loop access analysis should return forward dependence and thus the loop can be vectorized. Any comments? Thanks, Jin #define N 1000 double

On 06/11/2018 02:33 PM, Friedman, Eli via llvm-dev wrote: > On 6/11/2018 10:06 AM, jingu at codeplay.com via llvm-dev wrote: >> Hello All, >> >> I have met one may-alias case from llvm's alias analysis. The code >> snippet is as following: >> >> char buf[4]; >> >> void test (int idx) { >> char *a = &buf[3 - idx]; >> char *b =

Hello All, I have a question about a May-alias case. Let's look at one simple C example. char *buf[4]; char c; void test(int idx) {   char *a = buf[3 - idx];   char *b = buf[idx];   *a = *b;   c++;   *a = *b; } We can imagine the second "*a = *b" could be removed. Let's look at the IR snippet with -O3 for above example.   1 define void @test(i32 %idx) {   2 entry:  

Hi, I have the following C loop to vectorize: struct box { double* source; }; void test(double* restrict result, struct box my_struct, int len) { for (int i=0 ; i<len; i++) { result[i] = my_struct.source[i] * my_struct.source[i]; } } There are two references in the loop, result[i] (restrict) and my_struct.source[i] (readonly). The compiler should easily figure out that

BTW, I have found why it doesn't work for arrays. TBAA information propagation is not implemented in CodeGenFunction::EmitArraySubscriptExpr with "TODO: Preserve/extend path TBAA metadata?". On Fri, Dec 4, 2015 at 1:38 PM, Dmitry Polukhin <dmitry.polukhin at gmail.com> wrote: > As far as I can see it is specifics of arrays inside structs. Current TBAA > does distinguish

Hi Devs, I am looking at the bug https://bugs.llvm.org/show_bug.cgi?id=43953 and found that following piece of ir %arrayidx = getelementptr inbounds float, float* %Vec0, i64 %idxprom %0 = load float, float* %arrayidx, align 4, !tbaa !2 %arrayidx2 = getelementptr inbounds float, float* %Vec1, i64 %idxprom %1 = load float, float* %arrayidx2, align 4, !tbaa !2 %sub = fsub fast float %0, %1

Jeroen, thank you for very useful link with the context. Indeed union cases are very complicated and I see places in code when TBAA gives up. Daniel, I completely agree that TBAA has limited power and can solve relatively simple cases only. So anything more complicated that involves intermediate variables that points to struct or array elements cannot be solved by TBAA alone. Differentiating

Hi, Does this kind of IR have "undefined behavior" under LLVM semantics or is it acceptable? (TLDR: a store of i64 at offset n, followed by a load of i32 at offset n+1.) define void @foo(i32* %A, i64 %n) { entry: %arrayidx = getelementptr inbounds i32, i32* %A, i64 %n %arrayidx_cast = bitcast i32* %arrayidx to i64* store i64 0, i64* %arrayidx_cast, align 4 %add1 = add i64 %n,

Hi Andrew, The issue below refers to LSR, so I'll appreciate your feedback. It also refers to instruction combining and might impact backends other than X86, so if you know of others that might be interested you are more than welcome to add them. Thanks, Anat _____________________________________________ From: Shemer, Anat Sent: Tuesday, February 18, 2014 15:07 To: 'llvmdev at

Hi, Look at the following code: Look at the following C code seqence: unsigned char mainGtU ( unsigned int i1, unsigned int i2, unsigned char* block) { unsigned char c1, c2; c1 = block[i1]; c2 = block[i2]; if (c1 != c2) return (c1 > c2); i1++; i2++; c1 = block[i1]; c2 = block[i2]; if (c1 != c2) return (c1 > c2); i1++; i2++; .. ..

Hi Daniel, I see your point about LLVM and C/C++ type agnostic. I think TBAA was invented to partially cover this gap and give optimization opportunities when LLVM types are not sufficient but C/C++ types have required information. What do you think about following example: struct S { int a[10]; int b; }; int foo(struct S *ps, int i) { ps->a[i] = 1; ps->b = 2; return

Hello everyone, This week I was looking into the following example ( https://godbolt.org/z/uhgQcq) where two constants are written to a local array and an input argument, masked and shifted, is used to select between them. The possible values for the CC variable are 0 and 1, so I'm expecting that at the maximum level of optimizations the two constants are actually propagated, resulting in the

Hi all, One of the reasons the Livermore Loops couldn't be vectorized is that it was using global structures to hold the arrays. Today, I'm investigating why is that so and how to fix it. My investigation brought me to LoopVectorizationLegality::canVectorizeMemory(): if (WriteObjects.count(*it)) { DEBUG(dbgs() << "LV: Found a possible read/write reorder:"

Hi, I'm trying to optimize a simple C code and came across a situation where invariant code is not being moved out: On an -O3 compilation, I noticed that the "load" for the loop bounds (which remain invariant throughout) happens on each iteration of both the loops, even though it is not modified anywhere in the function "bigLoop". It seems that alias analysis is not able

Hi, Is the -indvars pass functional? I've done some small test to check it, but this fails to canonicalize: > int *x; > int *y; > int i; > ... > for (i = 1; i < 100; i+=2) { > x[i] = y[i] + 3; > } The IR produced after -indvars: > br label %for.cond > > for.cond: ; preds = %for.inc, %entry > %indvars.iv =

Hi All, I've been successfully using the with function for analyses and the transform function for multiple transformations. Then I thought, why not use "with" for both? I ran into problems & couldn't figure them out from help files or books. So I created a simplified version of what I'm doing: rm( list=ls() ) x1<-c(1,3,3) x2<-c(3,2,1) x3<-c(2,5,2)

On Fri, Mar 13, 2015 at 2:54 PM Daniel Berlin <dberlin at dberlin.org> wrote: > On Fri, Mar 13, 2015 at 2:39 PM Olivier H Sallenave <ohsallen at us.ibm.com> > wrote: > >> Hi, >> >> I have the following C loop to vectorize: >> >> struct box { >> double* source; >> }; >> >> void test(double* restrict result, struct box