similar to: [LLVMdev] proposed new rule for getelementptr

On Jul 22, 2009, at 1:30 PM, Dan Gohman wrote: > Hello, > > I'm working on refining the definition of getelementptr (GEP) to > clarify its semantics and to allow front-ends to provide additional > information to optimization passes. It would be quite valuable to have cleaner semantics for GEPs, both for LLVM in general and for the memory safety work we have been doing in

On Jul 23, 2009, at 1:59 AM, Mark Shannon wrote: > Hi Dan, > > What you are proposing is a major change in the semantics of llvm. > > You are taking certain uses of an instruction that have well defined > behaviour and undefining them. > > Have you made any estimate of how many peoples' code this may or may > not > break? > > I think this is a *very* bad

On Wed, Jul 22, 2009 at 11:30 AM, Dan Gohman<gohman at apple.com> wrote: >  - The result value of an allocation instruction is associated with >    the address range of the allocated storage. Might want to clarify this to include calloc/realloc. >  - A null pointer is associated with no addresses. A null pointer in address space 0. >  - A pointer value formed by a ptrtoint is

Hi Dan, What you are proposing is a major change in the semantics of llvm. You are taking certain uses of an instruction that have well defined behaviour and undefining them. Have you made any estimate of how many peoples' code this may or may not break? I think this is a *very* bad idea. Let me make some more detailed comments: Dan Gohman wrote: > Hello, > > I'm working

On Wednesday 22 July 2009 13:30, Dan Gohman wrote: > - A pointer value formed by a ptrtoint is associated with all address > ranges of all pointer values that contribute (directly or > indirectly) to the computation of the pointer's value. Do you mean inttoptr here? And that "all pointer values that contribute (directly or indirectly) to the computation of the

I have a question about when we should apply these pointer aliasing rules. Do the rules tell us when a load/store is safe? "Any memory access must be done through a pointer value associated with an address range of the memory access, otherwise the behavior is undefined." So this means the conversion discussed here is still safe in terms of memory safety, but its meaning after conversion

On Wed, Apr 20, 2011 at 12:20 PM, Eli Friedman <eli.friedman at gmail.com> wrote: > On Wed, Apr 20, 2011 at 8:08 AM, Jianzhou Zhao <jianzhou at seas.upenn.edu> wrote: >> I have a question about when we should apply these pointer aliasing >> rules. Do the rules tell us when a load/store is safe? >> "Any memory access must be done through a pointer value

Consider the two functions bellow: define i8* @f(i8* %A) { %pti = ptrtoint i8* %A to i64 %add = add i64 %pti, 5 %itp = inttoptr i64 %add to i8* ret i8* %itp} define i8* @g(i8* %A) { %gep = getelementptr i8* %A, i64 5 ret i8* %gep} What, if anything, prevents us from canonicalizing @f to @g?I've heard that this might be in violation of http://llvm.org/docs/LangRef.html#pointeraliasing

On Wed, Apr 20, 2011 at 8:08 AM, Jianzhou Zhao <jianzhou at seas.upenn.edu> wrote: > I have a question about when we should apply these pointer aliasing > rules. Do the rules tell us when a load/store is safe? > "Any memory access must be done through a pointer value associated > with an address range of the memory access, otherwise the behavior is > undefined." >

On 2009-07-22 21:30, Dan Gohman wrote: > Hello, > > I'm working on refining the definition of getelementptr (GEP) to > clarify its semantics and to allow front-ends to provide additional > information to optimization passes. > > To help support this, I'd like to propose the following rule: > > Any memory access must be done though a pointer value associated >

On Jul 22, 2009, at 1:28 PM, Török Edwin wrote: > On 2009-07-22 21:30, Dan Gohman wrote: > >> Hello, >> >> >> >> I'm working on refining the definition of getelementptr (GEP) to >> >> clarify its semantics and to allow front-ends to provide additional >> >> information to optimization passes. >> >> >> >> To

On Wed, Apr 20, 2011 at 10:21 AM, Jianzhou Zhao <jianzhou at seas.upenn.edu> wrote: > On Wed, Apr 20, 2011 at 12:20 PM, Eli Friedman <eli.friedman at gmail.com> wrote: >> On Wed, Apr 20, 2011 at 8:08 AM, Jianzhou Zhao <jianzhou at seas.upenn.edu> wrote: >>> I have a question about when we should apply these pointer aliasing >>> rules. Do the rules tell

On Wed, Apr 20, 2011 at 2:11 PM, Eli Friedman <eli.friedman at gmail.com> wrote: > On Wed, Apr 20, 2011 at 10:21 AM, Jianzhou Zhao <jianzhou at seas.upenn.edu> wrote: >> On Wed, Apr 20, 2011 at 12:20 PM, Eli Friedman <eli.friedman at gmail.com> wrote: >>> On Wed, Apr 20, 2011 at 8:08 AM, Jianzhou Zhao <jianzhou at seas.upenn.edu> wrote: >>>> I

On 2009-07-22 21:30, Dan Gohman wrote: > Hello, > > I'm working on refining the definition of getelementptr (GEP) to > clarify its semantics and to allow front-ends to provide additional > information to optimization passes. > > To help support this, I'd like to propose the following rule: > > Any memory access must be done though a pointer value associated >

LLVM 2.7's ScalarEvolution.cpp has this scary comment: // It's tempting to handle inttoptr and ptrtoint as no-ops, however this can // lead to pointer expressions which cannot safely be expanded to GEPs, // because ScalarEvolution doesn't respect the GEP aliasing rules when // simplifying integer expressions. I think I understand what the comment is saying. If a GEP has

On 4/4/2011 6:45 PM, Eli Friedman wrote: > On Mon, Apr 4, 2011 at 5:02 PM, Arushi Aggarwal<arushi987 at gmail.com> wrote: >> >>> Hi, >>> Is it correct to convert, >>> %196 = load i32* %195, align 8 ;<i32> [#uses=1] >>> %197 = zext i32 %196 to i64 ;<i64> [#uses=1] >>> %198 =

On Sep 9, 2010, at 1:48 PM, David Greene wrote: > LLVM 2.7's ScalarEvolution.cpp has this scary comment: > > // It's tempting to handle inttoptr and ptrtoint as no-ops, however this can > // lead to pointer expressions which cannot safely be expanded to GEPs, > // because ScalarEvolution doesn't respect the GEP aliasing rules when > // simplifying integer

On Mon, Sep 8, 2014 at 4:22 PM, Dan Gohman <dan433584 at gmail.com> wrote: > It looks a little silly to say this in the case of the integer constant 5, > and there are some semantic gray areas around extra-VM allocation, but the > same thing happens if the add were adding a dynamic integer value, and then > it's difficult to find a way to separate that case from the constant

On 09/08/2014 04:22 PM, Dan Gohman wrote: > An object can be allocated at virtual address 5 through extra-VM means > (eg. mmap), and then one can (creatively) interpret the return value > of @f as being associated with whatever %A was associated with *and* > 5. The return value of @g can only be associated with exactly the same > set that %A was associated with. Consequently,

On Mon, Apr 4, 2011 at 7:10 AM, John Criswell <criswell at illinois.edu> wrote: > On 4/4/2011 6:45 PM, Eli Friedman wrote: >> >> On Mon, Apr 4, 2011 at 5:02 PM, Arushi Aggarwal<arushi987 at gmail.com> >>  wrote: >>> >>>> Hi, >>>> Is it correct to convert, >>>>   %196 = load i32* %195, align 8