similar to: [LLVMdev] Address of labels = 1 with llvm-g++

Hi, I have a question on why gcc and llvm-gcc compile the following simple code snippet differently: extern int a; extern int *b; void foo() { int i; for (i = 1; i < 100; ++i) a += b[i]; } gcc compiles this function hoisting the load of the global variable "b" outside of the loop, while llvm-gcc keeps it inside the loop. This results in slower code on the part of

Hi Devs, consider below testcase $cat test.cpp constexpr int product() { return 10*20; } int main() { const int x = product(); return 0; } $./clang test.cpp -std=c++11 -S $./clang -v clang version 9.0.0 Target: x86_64-unknown-linux-gnu $cat test.s main: .cfi_startproc # %bb.0: pushq %rbp .cfi_def_cfa_offset 16 .cfi_offset %rbp, -16 movq

I write a small function and test it under clang and gcc, filet test.c: double X[100]; double Y[100]; double DA = 0.3; int f() { int i; for (i = 0; i < 100; i++) Y[i] = Y[i] - DA * X[i]; return 0; } clang -S -O3 -o test.s test.c -march=native -ccc-echo result: "D:/work/trunk/bin/Release/clang.exe" -cc1 -triple i686-pc-win32 -S -disable-fr e -disable-llvm-verifier

Hi, Structures are passed by pointer, so the return value is not actually in eax. That code gets transformed into something like: void sum(A1 *out, const A1 one, const A1 two) { out->x = one.x + two.x out->y = one.y + two.y } So actually the function ends up returning void and operating on a hidden parameter, so %eax is dead at the end of the function and should not be being relied

the clang 3.5 loop optimizer seems to jump in unintentional for simple loops the very simple example ---- const int SIZE = 3; int the_func(int* p_array) { int dummy = 0; #if defined(ITER) for(int* p = &p_array[0]; p < &p_array[SIZE]; ++p) dummy += *p; #else for(int i = 0; i < SIZE; ++i) dummy += p_array[i]; #endif return dummy; } int main(int argc, char** argv) {

Hi r-devel, a recent install of R-3.4.0 RC (2017-04-13 r72510)? on Linux (Ubuntu 16.04.1 LTS) x86_64-linux-gnu? with?g++ (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609 (see?http://bioconductor.org/checkResults/devel/bioc-LATEST/malbec2-NodeInfo.html?for more)? results in CXXFLAGS not containing "-O2" as optimisation flag, there is only " -Wall", while?CFLAGS are happy with

On 10/12/2016 2:22 PM, Alex Bradley wrote: > > > > You probably want to look at the x86 backend; it has a lot of > instructions which involve both computation and memory. Take the > following IR, a variant of your example: > > > > define void @foo(i32 *%a, i32 *%b, i32 *%c) { > > entry: > > %0 = load i32, i32* %a, align 4 > > %1 = load i32,

Hi, As you told that function ends up returning void, I just confirmed it in the IR, the function is defined as: define *void* @_Z3sum2A1S_(*%struct.A1* noalias sret %agg.result*, %struct.A1* byval align 4 %one, %struct.A1* byval align 4 %two). But when i checked the register values in g++, eax contains an address of stack, which points to the value (object) returned by sum. That is if we

On Sep 1, 2010, at 6:25 AM, Argyrios Kyrtzidis wrote: > The attached .ll files seem equivalent, but the resulting asm from 'opt-fail.ll' causes a crash to webkit. > I suspect the usage of registers is wrong, can someone take a look ? The difference is that there is a shift right after the multiply, before the divide. In IR, the difference is: %5 = mul nsw i32 %4, %tmp1

Hi Rafael, Yes, merging gv prevents linker to do garbage collection. Should it be implemented as a peephole pass? If we do it too early, the distance between GVs are not fixed yet. PS: Below is the GCC output with "extern" hidden: ldr r2, .L2 stmfd sp!, {r3, lr} .save {r3, lr} .LPIC0: add r0, pc, r2 bl _Z4initPv(PLT) ldr r1, .L2+4 .LPIC1: add r0, pc, r1 bl _Z4initPv(PLT) ldr

The attached .ll files seem equivalent, but the resulting asm from 'opt-fail.ll' causes a crash to webkit. I suspect the usage of registers is wrong, can someone take a look ? $ llc opt-pass.ll -o - .section __TEXT,__text,regular,pure_instructions .globl __ZN7WebCore6kolos1ERiS0_PKNS_20RenderBoxModelObjectEPNS_10StyleImageE .align 4, 0x90

On 8 Aug 2013, at 04:23, Pete Cooper <peter_cooper at apple.com> wrote: > > On Aug 7, 2013, at 7:23 PM, Michele Scandale <michele.scandale at gmail.com> wrote: > >> On 08/08/2013 03:52 AM, Pete Cooper wrote: >> >> From here I understand that in the IR there are addrspace(N) where N=0,1,2,3,... according to the target independent mapping done by the

Problem seems not only with operator overloading, It occurs with struct value returning also. gdb while debugging expects the return value in eax, gcc does returns in eax, But Clang returns in edx(it can be checked in gdb by printing the contents of edx). Code(sample code) struct A1 { int x; int y; }; A1 sum(const A1 one, const A1 two) { A1 plus = {0,0}; plus.x = one.x + two.x; plus.y

Sorry I missed that important detail. The relevant part of the command line is: -cc1 -S -triple i386-pc-win32 I don't expect it matters if it's for Windows or Linux in this case. On Fri, Sep 14, 2018 at 9:16 PM David Blaikie <dblaikie at gmail.com> wrote: > Can't say I've observed that behavior (though I'm just building from > top-of-tree rather than 6.0,

On 08/08/2013 11:04 AM, David Chisnall wrote: > What happens when I link together two IR modules from different front ends that have different language-specific address spaces? I agree with Micah: if during the linking two IR modules there are incoherences (e.g. in module1 2 -> 1 and in module2 2 -> 3) then the modules are incompatible and the link process should fail. > I would be

When I try running one llvm function in JIT without optimization I get SEGV. Looking at assembly (below) I see that the local value 0xffffffffffffffe0(%rbp) is used without being ever initialized (see my comment in asm). Same code on i386 works fine, with and w/out optimization. My guess is that this is a bug in LLVM. Yuri --- llvm --- %struct.mystruct = type { i32, i8, i8, i8, i8 } define

Hello all, In r223757 I've committed a patch that performs, for the 32-bit x86 calling convention, the transformation of MOV instructions that push function arguments onto the stack into actual PUSH instructions. For example, it will transform this: subl $16, %esp movl $4, 12(%esp) movl $3, 8(%esp) movl $2, 4(%esp) movl $1, (%esp) calll _func addl $16, %esp

Hi everyone, I found that LLVM generates redundant code when calling functions with constant parameters, with optimizations disabled. Consider the following C code snippet: int foo(int x, int y); void bar() { foo(1, 2); foo(3, 4); } Clang/LLVM 6.0 generates the following assembly code: _bar: subl $32, %esp movl $1, %eax movl $2, %ecx movl $1, (%esp) movl $2, 4(%esp) movl %eax, 28(%esp) movl

Hello all! When I compile the following more or less stupid functions with clang++ -O3 -S test.cpp ===> int test_register(int x) { x ^= (x >> 2); x ^= (x >> 3); x = x ^ (x >> 4); int y = x; x >>= 5; x ^= y; // almost the same but explicit return x; } int test_scheduler(int x) { return ((x>>2) & 15) ^ ((x>>3) & 31); }

Which performance guidelines are you referring to? I'm not that familiar with decade-old CPUs, but to the best of my knowledge, this is not true on current hardware. There is one specific circumstance where PUSHes should be avoided - for Atom/Silvermont processors, the memory form of PUSH is inefficient, so the register-freeing optimization below may not be profitable (see 14.3.3.6 and