similar to: [LLVMdev] Phi nodes

Hi Thanks for your answers so far. I am currently stumbling into new questions. Naive as i am, i thought that the llvm-bytecode is allways in SSA form. But this doesn't seem to be the case. At least there are no phi instructions embedded if the bytecode drops out of llvm-gcc? Looking into the archives this has been discussed before:

Hi, I am emitting llvm bit code using llvm-gcc -c -emit-llvm -O0 -o test.bc test.c and then optimizing it with opt -O3 -print-module test.bc in order to obtain a dump of generated IR. The resulting code has Phi nodes and is perhaps in SSA form. I want to undo the SSA form while retaining all the other optimizations. Is mem2reg the right optimization to be added after -O3, i.e., opt -O3

On 01/22/2011 10:30 PM, Surinder wrote: > Hi, > > I am emitting llvm bit code using > > llvm-gcc -c -emit-llvm -O0 -o test.bc test.c > > and then optimizing it with > > opt -O3 -print-module test.bc > > in order to obtain a dump of generated IR. > > > The resulting code has Phi nodes and is perhaps in SSA form. I want > to undo the SSA form while

Hi, I work on a pass that requires as input LLVM code without any phi nodes. For this, I use the reg2mem pass which produces suitable code, the pass runs correctly, but I obtain a significant performance decrease. I expect that this is because there are more reads / writes to memory after running the reg2mem pass. How can I optimize the code, without inserting any phi nodes? Or is there a

Hi, I am interested in SSA and read llvm uses SSA in its ir. I decided to write a simple program and compile it with llvm to the human readable assembly language representation of the ir. I expected phi nodes all over the place. However, I could not find a single one! Could you tell my why that is so? I compiled with "llvm-gcc -emit-llvm test.c -S -o test.ll". Attached to this message

Chayan Sarkar wrote: > Hi, > I am new to llvm. I have project in llvm. For that I need SSA form, > which is already implemented in llvm. Basically I want to know which > pass insert phi and converts it to SSA form in llvm . http://llvm.org/docs/Passes.html#mem2reg which is lib/Transforms/Utils/PromoteMemoryToRegister.cpp. Nick

On Fri, 9 Jul 2004, Vladimir Prus wrote: > Misha Brukman wrote: > > > LLVM Machine code is in SSA. > > This explains quite a lot. I though it's possible to just reduce convert phis > into copy instructions in predecessors -- all of which will have the same > destination register. There are algorithms for eliminating PHI nodes, but they aren't quite so simple.

Hi Andrew, > Somewhere during optimization PHI nodes on pointer types (including > alloca instructions) are being introduced, and they persist through the > scalar replacement of aggregates pass and others. I can't seem to find > a combination of passes or transformations to get rid of them. Has > anyone had this problem before, and know a transformation to eliminate > it?

On 08/20/2012 03:46 PM, Duncan Sands wrote: > Hi Andrew, > >> Somewhere during optimization PHI nodes on pointer types (including >> alloca instructions) are being introduced, and they persist through the >> scalar replacement of aggregates pass and others. I can't seem to find >> a combination of passes or transformations to get rid of them. Has >> anyone

On Sep 13, 2010, at 10:46 AM, John McCall wrote: > On Sep 13, 2010, at 1:15 AM, Duncan Sands wrote: >>> I compiled with "llvm-gcc -emit-llvm test.c -S -o test.ll". >>> Attached to this >>> message are the source and the resulting ll output. >> >> compile with optimization. The llvm-gcc front-end "cheats" and >> stores/loads

On Sep 13, 2010, at 1:15 AM, Duncan Sands wrote: >> I compiled with "llvm-gcc -emit-llvm test.c -S -o test.ll". Attached to this >> message are the source and the resulting ll output. > > compile with optimization. The llvm-gcc front-end "cheats" and stores/loads all > values to/from memory, avoiding the need to construct phi nodes; instead it lets >

On Sep 13, 2010, at 10:58 AM, Fariborz Jahanian wrote: > On Sep 13, 2010, at 10:46 AM, John McCall wrote: >> On Sep 13, 2010, at 1:15 AM, Duncan Sands wrote: >>>> I compiled with "llvm-gcc -emit-llvm test.c -S -o test.ll". Attached to this >>>> message are the source and the resulting ll output. >>> >>> compile with optimization. The

Note, I'm CC'ing the list as it's important LLVM design kind of material. On Thu, 5 Feb 2004, Michael Kahl wrote: > I note that in your representation of phi nodes, you key the incoming > value to the incoming block. Both appear explicitly (in pairs) in the > operand list. There is even a method > "llvm::PHINode::getIncomingValueForBlock" which performs this

On Tuesday 27 January 2009 18:28, Eli Friedman wrote: > You can use a no-op bitcast for scalars, but there isn't any reliable > way to do it for all first-class values. Guh. > That said, I don't quite follow the issue. This is SSA, so the only way a > value can change is if you change the code. This isn't (yet) SSA. This is mem2reg turning things into SSA. >

On Jan 28, 2009, at 9:06 AM, David Greene wrote: > On Tuesday 27 January 2009 18:28, Eli Friedman wrote: > >> You can use a no-op bitcast for scalars, but there isn't any reliable >> way to do it for all first-class values. > > Guh. > >> That said, I don't quite follow the issue. This is SSA, so the >> only way a >> value can change is if

Misha Brukman wrote: > LLVM Machine code is in SSA. This explains quite a lot. I though it's possible to just reduce convert phis into copy instructions in predecessors -- all of which will have the same destination register. > gets you two definitions of r. So we have machine PHI nodes merge the > two possible values into one for result of r. These phis get removed > after

Chris and everyone else, Below I summarize my understanding of what llvm does when converting to SSA and a clarification on why backward dataflow analyses can not be performed on "just" SSA. >> Scalar variables still have a stack location associated with them, >> don't they? > > No, they don't. All scalar values in LLVM represent "virtual >

On 3/29/11 12:26 PM, George Baah wrote: > Hi All, > When I run the following command > llvm-gcc -03 -emit-llvm test.cpp -c -o test.bc or llvm-gcc -emit-llvm > test.cpp -c -o test.bc > > on the program test.cpp, the IR representation is not in SSA form. > I do not see any phi functions. Actually, it is in SSA form (or more precisely, the virtual registers are in SSA form;

Hi, LLVMers. I am trying to restore the original HL code from LLVM IR (kinda reverse engineering). However, I have no good idea about how to handle PHI nodes. It is quite tricky for me to deal with the PHI nodes in LLVM IR in order to restore the original-like code. I read some reverse engineering thesis but they are a little bit old so don't handle SSA form. Could you shed some lights on

Somewhere during optimization PHI nodes on pointer types (including alloca instructions) are being introduced, and they persist through the scalar replacement of aggregates pass and others. I can't seem to find a combination of passes or transformations to get rid of them. Has anyone had this problem before, and know a transformation to eliminate it? My optimization passes rely on