use-def chain questions

Hi, all,
We are working on a static analysis phase on LLVM’s IR, we want to do a backforward phase through the use-def chain, I knew that LLVM
had a built-in SSA form which provide the use-def chain for virtual register variables, however, I want to know if you also provide some kinds of use-def chain for memory operations? for example, I have the following source code

int foo(int *q, int *p) {
int x;
*p = 1;
x = *q;
return x;
}

the IR after front-end is:

s1: store i32* %q, i32** %q_addr
s2: store i32* %p, i32** %p_addr

s3: %1 = load i32** %p_addr, align 8 ; <i32*> [#uses=1]
s4: store i32 1, i32* %1, align 4

s5: %2 = load i32** %q_addr, align 8 ; <i32*> [#uses=1]
s6: %3 = load i32* %2, align 4 ; [#uses=1]
s7: store i32 %3, i32* %x, align 4

in the source code, I want to find the definition statement of “*q”, here since we do not know if p and q are aliased or not, we assume they are may-aliased, So I want to find the statement “*p = 1” as the define statement

in the IR code, s6 is the load instruction for “*p”, s4 is the store instruction for “*q”, is there existing infrastructure for us to use and find s4 directly?
I understand that I can traverse back every instruction, and compare the alias result to see if any instruction prior to it is define statement, but I am not sure if there is already better way to do that.

(2) another question
I am using the gold-plugin to compile large applications, it works very well, then, I want to add a pass into include/llvm/Support/StandardPasses.h: createStandardLTOPasses, Since I want to add a new phase and disable some existing phase, is there any way to pass some flag to do that, now my complication model is:

export PREFIX=/home/tianwei/llvm/llvm-gcc-bin/
export CC="$PREFIX/bin/llvm-gcc -use-gold-plugin"
export CXX="$PREFIX/bin/llvm-g++ -use-gold-plugin"
export AR="$PREFIX/bin/ar --plugin /home/tianwei/llvm/llvm-gcc-bin/libexec/gcc/x86_64-unknown-linux-gnu/4.2.1/libLLVMgold.so"
export NM="$PREFIX/bin/nm --plugin /home/tianwei/llvm/llvm-gcc-bin/libexec/gcc/x86_64-unknown-linux-gnu/4.2.1/libLLVMgold.so"
export RANLIB=/bin/true #ranlib is not needed, and doesn’t support .bc files in .a
export CFLAGS="-O2 --emit-llvm"
export LD_LIBRARY_PATH=/usr/local/lib:/home/tianwei/llvm/llvm-gcc-bin/lib/:$LD_LIBRARY_PATH
export PATH=/home/tianwei/llvm/llvm-gcc-bin/bin/:/home/tianwei/llvm/bin/bin/:$PATH
alias ar="$PREFIX/bin/ar --plugin /home/tianwei/llvm/llvm-gcc-bin/libexec/gcc/x86_64-unknown-linux-gnu/4.2.1/libLLVMgold.so"
alias nm="$PREFIX/bin/nm --plugin /home/tianwei/llvm/llvm-gcc-bin/libexec/gcc/x86_64-unknown-linux-gnu/4.2.1/libLLVMgold.so"
alias ranlib=/bin/true

the new ld which enable gold-plugin is installed in the PATH. Using these configuration, I can build apache/httpd successfully with its default make system. The trick here is that add “–emit-llvm” into CFLAGS, the “-c” will only produce llvm bytecode files. Also add “-use-gold-plugin” into CC, this is necessary since the make system usually use llvm-gcc as the link, llvm-gcc will pass “-use-gold-plugin” into final ld. ("-c" with -use-gold-plugin has no bad effect, also ld with --emit-llvm also has no bad effect, so this works).
But I want to how can I pass additional flag into libLTO as opt in this compilation model.

Thanks very much.

Tianwei

This is what the MemoryDependenceAnalysis pass is used for. Given a load (for example) it searches "up" the cfg to find a defining store or a clobbering value (e.g. a store which may alias the loaded pointer).

-Chris

Hi, all,
We are working on a static analysis phase on LLVM’s IR, we want to do a backforward phase through the use-def chain, I knew that LLVM
had a built-in SSA form which provide the use-def chain for virtual register variables, however, I want to know if you also provide some kinds of use-def chain for memory operations? for example, I have the following source code

int foo(int *q, int *p) {
int x;
*p = 1;
x = *q;
return x;
}

the IR after front-end is:

s1: store i32* %q, i32** %q_addr
s2: store i32* %p, i32** %p_addr

s3: %1 = load i32** %p_addr, align 8 ; <i32*> [#uses=1]
s4: store i32 1, i32* %1, align 4

s5: %2 = load i32** %q_addr, align 8 ; <i32*> [#uses=1]
s6: %3 = load i32* %2, align 4 ; [#uses=1]
s7: store i32 %3, i32* %x, align 4

in the source code, I want to find the definition statement of “*q”, here since we do not know if p and q are aliased or not, we assume they are may-aliased, So I want to find the statement “*p = 1” as the define statement

in the IR code, s6 is the load instruction for “*p”, s4 is the store instruction for “*q”, is there existing infrastructure for us to use and find s4 directly?
I understand that I can traverse back every instruction, and compare the alias result to see if any instruction prior to it is define statement, but I am not sure if there is already better way to do that.

This is what the MemoryDependenceAnalysis pass is used for. Given a load (for example) it searches “up” the cfg to find a defining store or a clobbering value (e.g. a store which may alias the loaded pointer).

Hi,Chris,
Thanks very much. I will look into the MemoryDependenceAnalysis phase to see how it works.
BTW, does anyone know my second question about passing flag to gold-plugin?

Thanks.

Tianwei