fallback: legalize: G_PHI <8 x s8>

Run:explore-04ca53e65f-20261014-114124
Kind:fallback
Category:legalize: G_PHI <8 x s8> NEW
Occurrences:2 in 2 configs, 2 test files
Snippet from:vlenb.c9074c1492.ll (mutant of vlenb.ll) @machine_licm via llvm-extract
Config:-O3 -mtriple=riscv32
Local check:reproduces at 04ca53e65f
Compiler Explorer:not uploaded (over --godbolt-limit or disabled)

Snippet:

@G.2 = external global <8 x i8>
@G.3 = external global <8 x i8>

define void @machine_licm() {
entry:
  %LGV = load <8 x i8>, ptr @G.2, align 8
  br label %loop

loop:                                             ; preds = %loop, %entry
  %0 = phi <8 x i8> [ splat (i8 16), %loop ], [ %LGV, %entry ]
  %v1 = call i32 @llvm.read_register.i32(metadata !0)
  call void @use(i32 %v1)
  store <8 x i8> %0, ptr @G.3, align 8
  br label %loop
}

declare void @use(i32)

; Function Attrs: nocallback nofree nosync nounwind willreturn memory(read)
declare i32 @llvm.read_register.i32(metadata) #0

attributes #0 = { nocallback nofree nosync nounwind willreturn memory(read) }

!0 = !{!"vlenb"}

Reproduce:

llc -O3 -mtriple=riscv32 -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel.* snippet.ll -o -
llc -O3 -mtriple=riscv32 -global-isel=0 snippet.ll -o -

Local llc output:

remark: <unknown>:0:0: unable to legalize instruction: %2:_(<8 x s8>) = G_PHI %5:_(<8 x s8>), %bb.2, %0:_(<8 x s8>), %bb.1 (in function: machine_licm)
warning: Instruction selection used fallback path for machine_licm

Occurrences (2):

InputFunctionConfig
aext-to-sext.52075f7d11.ll (mutant of aext-to-sext.ll)quux-mtriple=riscv64 -mattr=+m -verify-machineinstrs
vlenb.c9074c1492.ll (mutant of vlenb.ll)machine_licm-O3 -mtriple=riscv32

Generated 2026-10-15 08:05 UTC.