similar to: [LLVMdev] LLVM 2.8 and MMX

On Sep 8, 2010, at 7:24 AM, Eli Friedman wrote: > On Wed, Sep 8, 2010 at 12:35 AM, Nicolas Capens > <nicolas.capens at gmail.com> wrote: >> Hi Chris, >> >> It's not broken, but the performance is crippled. >> >> I noticed that the code still contains some MMX instructions, but several >> operations get expanded (apparently swizzling and such

On Wed, Sep 8, 2010 at 12:35 AM, Nicolas Capens <nicolas.capens at gmail.com> wrote: > Hi Chris, > > It's not broken, but the performance is crippled. > > I noticed that the code still contains some MMX instructions, but several > operations get expanded (apparently swizzling and such get expanded to a > large number of byte moves). I think some changes related to

Hi Bill, Comments inline: On 24/10/2011 9:50 PM, Bill Wendling wrote: > On Oct 20, 2011, at 8:42 AM, Nicolas Capens wrote: > >> Hi all, >> >> I'm working on a graphics project which uses LLVM for dynamic code >> generation, and I noticed a major performance regression when upgrading >> from LLVM 2.8 to 3.0-rc1 (LLVM 2.9 didn't support Win64 so I

Hi all, I've tested a recent revision and noticed that using 64-bit vectors became very slow. It looks like they are expanded to non-MMX instructions to avoid breaking code which does not clear the MMX state using emms? For my project I'm already manually inserting emms instructions in the right places, so I'd really like 64-bit vector operations to be lowered to MMX

On Oct 20, 2011, at 8:42 AM, Nicolas Capens wrote: > Hi all, > > I'm working on a graphics project which uses LLVM for dynamic code > generation, and I noticed a major performance regression when upgrading > from LLVM 2.8 to 3.0-rc1 (LLVM 2.9 didn't support Win64 so I skipped it > entirely). > > I found out that the performance regression is due to removing

On Oct 26, 2011, at 1:18 PM, Nicolas Capens wrote: > On 24/10/2011 9:50 PM, Bill Wendling wrote: >> On Oct 20, 2011, at 8:42 AM, Nicolas Capens wrote: >> >>> Hi all, >>> >>> I'm working on a graphics project which uses LLVM for dynamic code >>> generation, and I noticed a major performance regression when upgrading >>> from LLVM

Hi all, I'm working on a graphics project which uses LLVM for dynamic code generation, and I noticed a major performance regression when upgrading from LLVM 2.8 to 3.0-rc1 (LLVM 2.9 didn't support Win64 so I skipped it entirely). I found out that the performance regression is due to removing support for lowering 64-bit vector operations to MMX, and using SSE2 instead. My code uses a

On Mon, Aug 31, 2020 at 3:02 PM Eli Friedman <efriedma at quicinc.com> wrote: > Broadly speaking, I see two problems with implicitly enabling MMX > emulation on a target that has SSE2: > > > > 1. The interaction with inline asm. Inline asm can still have MMX > operands/results/clobbers, and can still put the processor in MMX mode. If > code is mixing MMX

I recently diagnosed a bug in someone else's software, which turned out to be due to incorrect MMX intrinsics usage: if you use any of the x86 intrinsics that accept or return __m64 values, then you, the *programmer* are required to call _mm_empty() before using any x87 floating point instructions or leaving the function. I was aware that this was required at the assembly-level, but not that

Assign the bug to me and I'll fix it in TOT next week! Thanks for narrowing it down! On Wednesday, September 22, 2010, Nicolas Capens <nicolas.capens at gmail.com> wrote: > Hi all, > > I think I figured it out: > 112804 causes 64-bit UNPCKLBW to no longer be selected for certain cases. > 112805 is benign. > 112806 causes 64-bit UNPCKHBW to no longer be selected for

This thread confuses me. I thought Chris said that LLVM 2.8 will not lower generic vectors to MMX because it breaks x87 code, and I didn't see an answer to your question about a switch to tell the code generator otherwise. However, you're complaining that MMX performance is subpar, even though LLVM 2.8 isn't supposed to generate MMX instructions. Can someone clarify the situation

Hi Nicolas, > I found out that the performance regression is due to removing support > for lowering 64-bit vector operations to MMX, and using SSE2 instead. My > code uses a mix of MMX intrinsics and v4i16 operations, so it ping-pongs > back and forth between MMX and SSE2 instructions in the generated code. > > To get more optimal code, I see three options, and I was wondering

LLVM isn't going to stop generating MMX instructions all together. We can't do that. :-) If the user specifically wants MMX (by, say, using the builtins), we have to support that still. The plan to cease generating MMX for generic vectors is a work-in-progress right now. It's not in 2.8. -bw On Sep 21, 2010, at 4:24 PM, Reid Kleckner wrote: > This thread confuses me. I thought

On Sep 21, 2010, at 5:30 PMPDT, Bill Wendling wrote: > LLVM isn't going to stop generating MMX instructions all together. We can't do that. :-) If the user specifically wants MMX (by, say, using the builtins), we have to support that still. The plan to cease generating MMX for generic vectors is a work-in-progress right now. It's not in 2.8. > > -bw Right, early on there

On Sep 21, 2010, at 10:23 AMPDT, Nicolas Capens wrote: > Hi all, > > Sorry for the late reply. I got sidetracked by other fun projects. ;-) > > I found that the performance regression is caused by revisions 112804, > 112805 and 112806. Those changes were made 2 days prior to the 2.8 > branching, so it may have not been the intention to include them there? > Either way

> This is a matter of presentation, but some of the "GCC extensions" are > standard C99 (now, at least). I noticed long long, C++-style comments > and designated initializers. > > I have plenty of complaints about the GCC documentation you're > pointing at, but this probably isn't the right forum for that. I do > think dropping "as fast as

On Feb 10, 2008, at 11:26 PM, Chris Lattner wrote: >> This is a matter of presentation, but some of the "GCC extensions" >> are >> standard C99 (now, at least). I noticed long long, C++-style >> comments >> and designated initializers. >> >> I have plenty of complaints about the GCC documentation you're >> pointing at, but this

On Sep 21, 2010, at 10:23 AM, Nicolas Capens wrote: > Hi all, > > Sorry for the late reply. I got sidetracked by other fun projects. ;-) > > I found that the performance regression is caused by revisions 112804, > 112805 and 112806. Those changes were made 2 days prior to the 2.8 > branching, so it may have not been the intention to include them there? > Either way they

Hi Dale, I suspect that these patches were intended to improve 128-bit vector performance but caused certain 64-bit vector operations to no longer lower to MMX instructions. Anyway, now that I've narrowed it down to these patches I think I can narrow it down further to a specific case so I can file a bug... Will Bruno be back soon or is he no longer working on the project for good? Cheers,

On Apr 14, 2011, at 12:47 PM, Eli Friedman wrote: >> I looked at the program using a debugger, and the pfadd instruction is >> executed correctly and the MMX register contains the correct values. >> The code that prepares the stack for the printf call seems to be >> messing it up. > > I would call that "user error"; basically, using MMX instructions >