search for: isdereferenceablepoint

I'm have a [PATCH] isDereferenceablePointer: look through gc.relocates and I want to know how to test this patch. So far, I've found one candiate: speculative execution in SimplifyCFG (test/Transforms/SimplifyCFG/SpeculativeExec.ll). However, it's somewhat involved to show that SimplifyCFG does kick in for gc.relocate. Is there a...

Given a pointer, does any addrspacecast affect the pointer's dereferenceablity ? For example, %pm = addrspaacecast float addrspacecast(n)* %pn to float addrspacecast(m)* %r = load float addrspace(m)* %pm In another word. the question is whether the following is true ? isDereferenceablePointer(pn) == isDereferenceablePointer(pm) [Note that the function is defined as Value.cpp:isDereferenceaablePointer(const Value*, ...) ] The reason I am asking this is that the current LLVM thinks the answer is yes (they are the same). But for the following case, it will make non-speculative l...

...erations on it. Nick You have to construct a > transformation which happens with the information you added and not > otherwise. > > The easiest case might be LICM. > > Philip > > On 01/17/2015 11:25 AM, Ramkumar Ramachandra wrote: >> I'm have a >> [PATCH] isDereferenceablePointer: look through gc.relocates >> >> and I want to know how to test this patch. So far, I've found one >> candiate: speculative execution in SimplifyCFG >> (test/Transforms/SimplifyCFG/SpeculativeExec.ll). However, it's >> somewhat involved to show that SimplifyC...

Eric Christopher wrote: > How are you trying to call it? Do you have a DataLayout? In test/Analysis/ValueTracking/memory-dereferenceable.ll, just change byval to dereferenceable(8), and %dparam won't match (see lib/IR/Value.cpp:521 for the logic that is supposed to fire). How do I get it to pass? I tried introducing a target-triple and target-datalayout, but it didn't help.

Hi, I've been debugging this issue for many hours, and would like a sanity check. The issue is that DL (DataLayout) is nullptr inside isDereferenceablePointer() no matter what I try. Why is DataLayout ever nullptr (shouldn't it get defaults?), and what should I do to make it non-nullptr? Thanks. Ram

...nters derived from allocas and global variables. But in other cases it scans the local BB to see if the pointer is already being loaded or stored from/to. In the latter case there can be a load/store with an alignment smaller than requested. In most cases this function is used in conjunction with isDereferenceablePointer: isDereferenceablePointer || isSafeToLoadUnconditionally. So if a pointer is dereferenceable there will be no alignment check. isSafeToSpeculativelyExecute doesn't care about alignment at all. It only checks for pointer dereferenceability. However according to the description it must check...

...of loops. At the moment, there doesn't seem to be a mechanism for doing so. There seem to be two ways of implementing this: either allow arbitrary instructions to be marked as safe and have Instruction::isSafeToSpeculativelyExecute return true for those or mark memory regions and extend Value::isDereferenceablePointer to return true for those. Is either of these a good idea? Or is there some other way to do this? FWIW, I quickly prototyped instruction marking using metadata and that seemed to work well enough for us. Roman

Hello, I was wondering how you can identify whether or not an Argument is a pointer. The "isDereferenceablePointer" function for Values doesn't seem to be what I want (I don't care whether or not the pointer points to allocated memory or is suitably aligned). I want to be able to discern between: i32* %pArray and i32 %pArray Thanks in advance. - John

...ment, there doesn't seem to be a mechanism for > doing so. There seem to be two ways of implementing this: either allow > arbitrary instructions to be marked as safe and have > Instruction::isSafeToSpeculativelyExecute return true for those or mark > memory regions and extend Value::isDereferenceablePointer to return true > for those. Is either of these a good idea? Or is there some other way to > do this? FWIW, I quickly prototyped instruction marking using metadata and > that seemed to work well enough for us. I think that marking the load with metadata would make sense. Is it safe to l...

...n't seem to be a mechanism for >> doing so. There seem to be two ways of implementing this: either allow >> arbitrary instructions to be marked as safe and have >> Instruction::isSafeToSpeculativelyExecute return true for those or mark >> memory regions and extend Value::isDereferenceablePointer to return true >> for those. Is either of these a good idea? Or is there some other way to >> do this? FWIW, I quickly prototyped instruction marking using metadata and >> that seemed to work well enough for us. > > I think that marking the load with metadata would make s...

You can use isPointerTy() in Type class. George On Mon, Aug 20, 2012 at 12:39 PM, John Backes <back0145 at umn.edu> wrote: > Hello, > > I was wondering how you can identify whether or not an Argument is a > pointer. The "isDereferenceablePointer" function for Values doesn't > seem to be what I want (I don't care whether or not the pointer points > to allocated memory or is suitably aligned). I want to be able to > discern between: > > i32* %pArray > > and > > i32 %pArray > > Thanks in advanc...

...n testcase, LICM will hoist everything except the div > instruction. LICM on ToT hoists the div. Even speculatively. The other thing is that div is just one example. The problem could also come up with an array load with an index could be safe to speculate if the index is known to be bounded. isDereferenceablePointer currently doesn't know how to do this, but it'll probably get smarter some day. Dan

> LICM on ToT hoists the div. Even speculatively. > > The other thing is that div is just one example. The problem could > also come up with an array load with an index could be safe to > speculate if the index is known to be bounded. isDereferenceablePointer > currently doesn't know how to do this, but it'll probably get > smarter some day. So, looking at just this example, it looks like semantics we assign to poison values have to do one of *) Avoid the udiv being moved, since a valid removal of nsw would create a program that is now...

2011/12/14 Rafael Ávila de Espíndola <rafael.espindola at gmail.com>: >> We first perform a speculation transformation, hoisting all of the >> code above the %overflow_check branch: >> >>   %t0 = add nsw i32 %a, %b >>   %t1 = sext i32 %t0 to i64 >>   %t2 = ashr i64 %t1, 31 >>   %t3 = add i64 %t2, 1 >>   %t5 = icmp ult %t3, 2 >>   %t6 =

Hi Everyone, I asked a question on the dev list related to the topic to which John Criswell and Jeremy Lakeman kindly provided some valuable insight. I'm still stuck on the issue and i'm hoping i didn't phrase the question well enough. I have a *foo.c* file that is : *#include <stdio.h>* *int foo(int a, int b){* * return a+b;* *}* *int main() {* *int x=foo(3,1); *