similar to: [LLVMdev] Question about compilation result - taking address of input array member

On Fri, Feb 1, 2013 at 12:11 PM, Eli Bendersky <eliben at google.com> wrote: > Hello, > > I'm playing around with some LEA-related code generation on x86-64 > (trunk LLVM & Clang), and I run into a case I don't understand: > > $ cat takeaddr.c > int* bar(int table[10]) { > return &table[2]; > } > > $ clang -cc1 -emit-llvm takeaddr.c > $

Hi Eli, I'm not sure if this is the answer you're looking for, but the alloca, store and load can be removed by the mem2reg pass, which isn't run by codegen prepare in llc. If you invoke clang with -O1 or above it will run mem2reg, producing IR that contains only the gep, and that produces the assembly you're looking for: $ clang -cc1 -emit-llvm -O1 takeaddr.c $ cat takeaddr.ll

John, I'm still not sure what you're talking about, I have included the assembly output from two compilations, one with a user explicit catch-all, one with only an implicit cleanup, the DWARF Action Table and Types Table are absolutely identical, as are the indexes used to reference the Action Table from the region maps. -Peter Lawrence.

Hi the appended IR code does not optimize to my liking :) this is the interesting part in x86_64, that got produced via clang -Os: --- movq -16(%r12), %rax movl -4(%rax), %ecx andl $2298949, %ecx ## imm = 0x231445 cmpq $2298949, (%rax,%rcx) ## imm = 0x231445 leaq 8(%rax,%rcx), %rax cmovneq %r15, %rax movl $2298949, %esi ## imm = 0x231445 movq %r12, %rdi movq %r14,

Hello Has there been any progress on this topic ? The 3.9 optimizer output is still the same as I just looked. https://llvm.org/bugs/show_bug.cgi?id=24448 Ciao Nat! Sanjay Patel schrieb: > [cc'ing Zia] > > We have this transform with -Os for some cases after: > http://reviews.llvm.org/rL244601 > http://reviews.llvm.org/D11363 > > but something in this example is

Dear All, I am working on a x86 backend machineFunction pass, where I am trying to save the hard coded address of an arbitrary machine basic block to memory in ASM. I know the assembly needed for this but am lost at how to construct the BuildMI(). Note that these machine basic blocks are not entry's to a function. but in the middle of the function. so using addGlobalAddress or

Hello Mentors, I am currently finding bug in Local Function related optimization due to which runtime failures are observed in some test cases, as those test cases are containing very large function with recursion and object oriented code so I am not able to find a pattern which is causing failure. So I tried following simple case to understand expected behavior from this optimization. Consider

Dear Mr. Northover, Thank you for the quick reply. You are correct about the address-mode operands :) . I guess an important detail left out was that the basic block (call it A) that wants to calculate the address of the target stationary trampoline basic block (call it B) will be moved around in memory during run-time. Our earlier solution, before the feature was implemented to move around (A)

On Sun, May 11, 2014 at 8:19 AM, Stephan Tolksdorf <st at quanttec.com> wrote: > Hi, > > When clang/LLVM can't prove that a noexcept function only contains > non-throwing code, it seems to insert an explicit exception handler that > calls std::terminate. Why doesn't clang leave it to the eh personality > function to call std::terminate when an exception is thrown

Hi I use BlockAddress to get the address of BasicBlock , and I use GlobalVariable 's getInitializer() to pass the address of BasicBlock to the global variable of my own program and then I print it out. But , I found that BlockAddress is not always correct. For example, some function's rsp (stack pointer) or other register is maintained by caller, so it would be like:

Change the assembly code to use only relative references of symbols for the kernel to be PIE compatible. Position Independent Executable (PIE) support will allow to extended the KASLR randomization range below the -2G memory limit. Signed-off-by: Thomas Garnier <thgarnie at google.com> --- arch/x86/entry/entry_64.S | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7

Changes: - patch v3: - Update on message to describe longer term PIE goal. - Minor change on ftrace if condition. - Changed code using xchgq. - patch v2: - Adapt patch to work post KPTI and compiler changes - Redo all performance testing with latest configs and compilers - Simplify mov macro on PIE (MOVABS now) - Reduce GOT footprint - patch v1: - Simplify ftrace

Changes: - patch v2: - Adapt patch to work post KPTI and compiler changes - Redo all performance testing with latest configs and compilers - Simplify mov macro on PIE (MOVABS now) - Reduce GOT footprint - patch v1: - Simplify ftrace implementation. - Use gcc mstack-protector-guard-reg=%gs with PIE when possible. - rfc v3: - Use --emit-relocs instead of -pie to reduce

Changes: - patch v2: - Adapt patch to work post KPTI and compiler changes - Redo all performance testing with latest configs and compilers - Simplify mov macro on PIE (MOVABS now) - Reduce GOT footprint - patch v1: - Simplify ftrace implementation. - Use gcc mstack-protector-guard-reg=%gs with PIE when possible. - rfc v3: - Use --emit-relocs instead of -pie to reduce

These patches make the changes necessary to build the kernel as Position Independent Executable (PIE) on x86_64. A PIE kernel can be relocated below the top 2G of the virtual address space. It allows to optionally extend the KASLR randomization range from 1G to 3G. Thanks a lot to Ard Biesheuvel & Kees Cook on their feedback on compiler changes, PIE support and KASLR in general. Thanks to

These patches make the changes necessary to build the kernel as Position Independent Executable (PIE) on x86_64. A PIE kernel can be relocated below the top 2G of the virtual address space. It allows to optionally extend the KASLR randomization range from 1G to 3G. Thanks a lot to Ard Biesheuvel & Kees Cook on their feedback on compiler changes, PIE support and KASLR in general. Thanks to

Changes: - patch v1: - Simplify ftrace implementation. - Use gcc mstack-protector-guard-reg=%gs with PIE when possible. - rfc v3: - Use --emit-relocs instead of -pie to reduce dynamic relocation space on mapped memory. It also simplifies the relocation process. - Move the start the module section next to the kernel. Remove the need for -mcmodel=large on modules. Extends

Changes: - patch v1: - Simplify ftrace implementation. - Use gcc mstack-protector-guard-reg=%gs with PIE when possible. - rfc v3: - Use --emit-relocs instead of -pie to reduce dynamic relocation space on mapped memory. It also simplifies the relocation process. - Move the start the module section next to the kernel. Remove the need for -mcmodel=large on modules. Extends

Hi I have some inline function C code, that llvm could be optimizing better. Since I am new to this, I wonder if someone could give me a few pointers, how to approach this in LLVM. Should I try to change the IR code -somehow- to get the code generator to generate better code, or should I rather go to the code generator and try to add an optimization pass ? Thanks for any feedback. Ciao

Hello, Here is my first speedup patch. Like 10-11%. No IDCT yet. Please feel free to comment my code or even better think about improvements. :) I belive my routines are not so bad, maybe one day they will be even more faster. What needs to be optimized is the loop filter fuction. I have no ideas now how to do it. It does not leave much space for parallel stuff, copying memory from lot of