similar to: [LLVMdev] getSmallConstantTripCount problem

In C code, if a loop is not a natural loop, that means its loop body should at least have one label, right? In that case, some BB out of the loop can jump to the loop body, so the loop has more than on entry. Does LoopInfo guarantee to identify all natural loops? This property is very important for my pass. regards, Bo On Fri, Apr 29, 2011 at 11:50 PM, Cameron Zwarich <zwarich at

Hi, I cannot find the getSmallConstantTripCount function in the current LLVM. Can anyone tell me whether there is still such a function to get the trip count in LLVM? Thank you very much. Best, Han

Hi, I found that some loops can not be identified by LoopInfo pass. For example, the loop at line 3094 of rdopt.c of benchmark 464.h264ref from spec cpu2006 is not a loop or a child (pr grandchild) of any loop in the loop list generated by LoopInfo pass. The documentation of LoopInfo says that it identifies natural loops, who have exactly one entry point. But the IR of this loops shows that

Hi, My pass heavily relies on llvm::Loop's getSmallConstantTripCount method. However, I found that it doesn't work for some simple cases. In the following example, I can get the constant trip count of the outermost loop if statement "a[l] = a[l] + 1" is there. After commenting out this line, the returned constant trip count for that loop is 0. In my pass, I traverse the nested

A natural loop is one whose header dominates all of the nodes in the loop. There is probably some block outside of the loop jumping to a block in the loop body. Cameron On Apr 29, 2011, at 7:43 PM, Bo Wu <bwu at cs.wm.edu> wrote: > Hi, > > I found that some loops can not be identified by LoopInfo pass. For example, the loop at line 3094 of rdopt.c of benchmark 464.h264ref from

On 4/30/11 8:52 AM, Bo Wu wrote: > In C code, if a loop is not a natural loop, that means its loop body > should at least have one label, right? In that case, some BB out of > the loop can jump to the loop body, so the loop has more than on entry. Off the top of my head, I would think you are right: a C label would have to exist within the loop in order to have a jump from outside the

Hi All, the attached patch performs the splitting in the proposed manner. before applying the patch, please execute svn cp lib/Transforms/Scalar/LoopUnroll.cpp lib/Transforms/Utils/UnrollLoop.cpp to make the patch apply and preserve proper history. Transforms/Utils/UnrollLoop.cpp contains the unrollLoop function, which is now used by the LoopUnroll pass. I've also moved the

Hello Matthijs, On May 9, 2008, at 3:47 AM, Matthijs Kooijman wrote: > Hi All, > > the attached patch performs the splitting in the proposed manner. > before applying the patch, please execute > svn cp lib/Transforms/Scalar/LoopUnroll.cpp lib/Transforms/Utils/ > UnrollLoop.cpp > to make the patch apply and preserve proper history. > > Transforms/Utils/UnrollLoop.cpp

I now understand that IndVarSimplify.cpp is capable of reproducing array references when the pointer initialization from the array address is found inside the immediately enclosing loop, such that in the following code: int A[20000], B[100], Z; int main() { int i, j, *a, *b; for ( a = &A[0], i = 0; i != 200; i++ ) for ( b = &B[0], j = 0; j != 100; j++

Hi all, I'm attempting to perform loop unrolling on a single function using the C++ API. Maybe I missed something in the docs, but I cannot figure out a way to do this. The function I'm working with is very simple, containing a single for loop and not much else. I compiled the function to IR using clang with no optimizations enabled. My initial plan was to first run the IndVarSimplify

Hello Matthijs, Separating mechanism from policy is a good thing for the LoopUnroll pass. Instead of moving the policy to a subclass though, I think it'd be better to move the mechanism, the unrollLoop function, out to be a standalone utility function, with the LoopInfo object passed in explicitly. FoldBlockIntoPredecessor would also be good to make into a standalone utility function, since

Hi I have the followed code for which I am writing a loop pass. int main() { int i = 0; for (i=0; i<20; i++) { printf ("hello world %d\n", i); } return 0; } In the function runOnLoop, I have the following instruction PHINode *indv = NULL; indv = L->getCanonicalInductionVariable(); However, when I check indv is always set to NULL. Since the code has a canonical

The loop rotation pass does modify the function, which I'm guessing means that a FunctionPassManager can be used to run LoopPasses (this is not obvious to me after looking through the FunctionPassManager code). Unfortunately none of the other passes I'm using (ScalarEvolution, LCSSA, IndVarSimplify, and LoopUnroll) appear to have an effect. I verified that the function can be loop

I've landed the patch in r324449. Before we merge this into two different Clang release branches and almost immediately release one of them, I would really like someone to confirm that this patch works well with the Linux kernel. David, if you're up for that, it would be great. Alternatively, Guenter or someone else here can help. On Tue, Feb 6, 2018 at 5:59 PM Chandler Carruth

Some of the LoopInfo APIs are preceeded by this comment: // Note that all of these methods can fail on general loops (ie, there may not // be a preheader, etc). For best success, the loop simplification and // induction variable canonicalization pass should be used to normalize loops // for easy analysis. These methods assume canonical loops. What Pass would that be? IndVarSimplify?

Hi Sriram, Thanks for performing this analysis. The problem here, both for memcpy and the vectorizer, is that we can’t predict the size of “n”, even though the only use of ’n’ is for the loop bound for the alloca [4 x [8 x i32]]. If you change the unroll condition to TC >= 0 then you will disable loop unrolling for all loops because getSmallConstantTripCount returns an unsigned number. You

Hello I'm wandring to know how many times a block is executed inside a loop ? knowing that I can't use getSmallConstantTripCount() because the number is unkown "for (i=0;i<N;i++) for example" I'm using a Function pass for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { if (Loop *L = LI->getLoopFor(BB)) { if (L->getHeader() ==

Hi, I am trying to get a small loop to *not vectorize* for cases where it doesn't make sense. For instance, this loop: void foo(int a[4][8], int n) { int b[4][8]; for(int i = 0; i < 4; i++) { for(int j = 0; j < n; j++) { a[i][j] = b[i][j]; } } } * Has maximum of 8ints copy. LLVM tries to use Memcpy for the inner loop. It is not helpful to perform

Hi Deepali, SCEV reports the backedge taken count as "((-1 * (sext i32 (3 + %x) to i64))<nsw> + ((sext i32 (3 + %x) to i64) smax (sext i32 (6 + %x) to i64)))", so symbolically it does have an answer. Ideally SCEV should be able to exploit <nsw> on (3 + %x) and (6 + %x) to fold the expression above to "3", but due to some systemic issues SCEV can't exploit

Thanks a lot for your guys' help!!! I guess once I am able to get *V* (which probably is a pointer to a Value object), then, I can instrument some code at the IR level to dump V. As long as I maintain V at this pass stage, I should be able to dump the loop trip count. This is true, isn't it? Basically, what I am going to do is to add a function call before the loop body, such as: