fallback: select: G

fallback: select: G_PREFETCH p0

Run:	explore-bc8218b282-20261015-075519
Kind:	fallback
Category:	select: G_PREFETCH p0
Occurrences:	20 in 2 configs, 1 test files
Snippet from:	xmips-cbop.ll @prefetch_data_read via llvm-extract
Config:	`-mtriple=riscv32 -mattr=+xmipscbop -verify-machineinstrs`
Local check:	reproduces at bc8218b282
Compiler Explorer:	not uploaded (over --godbolt-limit or disabled)

Snippet:

; Function Attrs: nounwind
define void @prefetch_data_read(ptr noundef %ptr) #0 {
entry:
  %arrayidx = getelementptr inbounds nuw i8, ptr %ptr, i64 1
  tail call void @llvm.prefetch.p0(ptr nonnull %arrayidx, i32 0, i32 0, i32 1)
  ret void
}

; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite, inaccessiblemem: readwrite)
declare void @llvm.prefetch.p0(ptr readonly captures(none), i32 immarg range(i32 0, 2), i32 immarg range(i32 0, 4), i32 immarg range(i32 0, 2)) #1

attributes #0 = { nounwind }
attributes #1 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite, inaccessiblemem: readwrite) }

Reproduce:

llc -mtriple=riscv32 -mattr=+xmipscbop -verify-machineinstrs -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel.* snippet.ll -o -
llc -mtriple=riscv32 -mattr=+xmipscbop -verify-machineinstrs -global-isel=0 snippet.ll -o -

Local llc output:

remark: <unknown>:0:0: cannot select: G_PREFETCH %2:gprb(p0), 0, 0, 1 :: (load unknown-size from %ir.arrayidx, align 1) (in function: prefetch_data_read)
warning: Instruction selection used fallback path for prefetch_data_read

Occurrences (20):

Input	Function	Config
xmips-cbop.ll	prefetch_data_read	`-mtriple=riscv32 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.ll	prefetch_data_write	`-mtriple=riscv32 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.ll	prefetch_inst_read	`-mtriple=riscv32 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.ll	prefetch_frameindex_test_neg	`-mtriple=riscv32 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.ll	prefetch_frameindex_test	`-mtriple=riscv32 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.ll	prefetch_data_read	`-mtriple=riscv64 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.ll	prefetch_data_write	`-mtriple=riscv64 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.ll	prefetch_inst_read	`-mtriple=riscv64 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.ll	prefetch_frameindex_test_neg	`-mtriple=riscv64 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.ll	prefetch_frameindex_test	`-mtriple=riscv64 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.0ab9300957.ll (mutant of xmips-cbop.ll)	prefetch_data_read	`-mtriple=riscv32 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.0ab9300957.ll (mutant of xmips-cbop.ll)	prefetch_inst_read	`-mtriple=riscv32 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.55de5eb792.ll (mutant of xmips-cbop.ll)	prefetch_data_read	`-mtriple=riscv64 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.55de5eb792.ll (mutant of xmips-cbop.ll)	prefetch_inst_read	`-mtriple=riscv64 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.5dad86e88b.ll (mutant of xmips-cbop.ll)	prefetch_frameindex_test_neg	`-mtriple=riscv32 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.625b2ff234.ll (mutant of xmips-cbop.ll)	prefetch_data_write	`-mtriple=riscv64 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.625b2ff234.ll (mutant of xmips-cbop.ll)	prefetch_inst_read	`-mtriple=riscv64 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.78d0685e75.ll (mutant of xmips-cbop.ll)	prefetch_data_write	`-mtriple=riscv32 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.78d0685e75.ll (mutant of xmips-cbop.ll)	prefetch_inst_read	`-mtriple=riscv32 -mattr=+xmipscbop -verify-machineinstrs`
xmips-cbop.b030d6ece2.ll (mutant of xmips-cbop.ll)	prefetch_frameindex_test_neg	`-mtriple=riscv64 -mattr=+xmipscbop -verify-machineinstrs`

Generated 2026-10-15 08:05 UTC.