lib/60614: Assert in gallium llvmpipe on Ryzen 9 7900

["stix%stix.id.au@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60614
>Category:       lib
>Synopsis:       Assert in gallium llvmpipe on Ryzen 9 7900
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    lib-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Aug 17 12:20:00 +0000 2026
>Originator:     Paul Ripke
>Release:        NetBSD 11.0_STABLE 20260816
>Organization:
Paul Ripke
"Great minds discuss ideas, average minds discuss events, small minds
 discuss people."
-- Disputed: Often attributed to Eleanor Roosevelt. 1948.
>Environment:
System: NetBSD slave 11.0_STABLE NetBSD 11.0_STABLE (SLAVE) #0: Sat Aug 15 09:42:47 AEST 2026 stix@slave:/home/netbsd/netbsd-11/obj.amd64/home/netbsd/netbsd-11/src/sys/arch/amd64/compile/SLAVE amd64
Architecture: x86_64
Machine: amd64
>Description:

I am using llvmpipe due to lack of support. In netbsd-10, this worked without
issues. After upgrading to netbsd-11, some apps started failing, including
prusaslicer, freecad, xroar, etc. Failed assertions like:

libEGL warning: DRI2: failed to authenticate                                                                                                                                                                                                                                                                               
DefIdx 1 exceeds machine model writes for early-clobber renamable $ymm5, dead early-clobber renamable $ymm0 = VPGATHERDDYrm killed renamable $ymm5(tied-def 0), renamable $rcx, 1, killed renamable $ymm1, 0, $noreg, killed renamable $ymm0(tied-def 1) :: (load 32, align 1)                                             
 (Try with MCSchedModel.CompleteModel set to false)incomplete machine model                                                                                                                                                                                                                                                
UNREACHABLE executed at /home/netbsd/netbsd-11/src/external/apache2/llvm/librt/libLLVMCodeGen/../../lib/../dist/llvm/lib/CodeGen/TargetSchedule.cpp:246!                                                                                                                                                                   
Abort (core dumped)                                                                                                                                                                                                                                                                                                        

Some apps are still fine with OpenGL, e.g. chromium with webglsamples.

Additionally, starting apps with 'GALLIUM_DRIVER=softpipe' also works, but is
unusably slow.

>How-To-Repeat:

Start OpenGL app using llvmpipe. Likely only applies to Zen3 or Zen4
architectures, based on the patch below.
	
>Fix:

The following avoids the specific assertion above; I had also tried defining
NDEBUG, which just resulted in other assertions elsewhere, or build failures.

diff --git a/external/apache2/llvm/dist/llvm/lib/Target/X86/X86ScheduleZnver3.td b/external/apache2/llvm/dist/llvm/lib/Target/X86/X86ScheduleZnver3.td
index fae9b1b51ef1..1229f68760a5 100644
--- a/external/apache2/llvm/dist/llvm/lib/Target/X86/X86ScheduleZnver3.td
+++ b/external/apache2/llvm/dist/llvm/lib/Target/X86/X86ScheduleZnver3.td
@@ -60,7 +60,7 @@ def Znver3Model : SchedMachineModel {
 
   let PostRAScheduler = 1; // Enable Post RegAlloc Scheduler pass.
 
-  let CompleteModel = 1;
+  let CompleteModel = 0;
 }
 
 let SchedModel = Znver3Model in {