fallback: legalize: G_LSHR <2 x s64>

Run:	explore-bc8218b282-20261015-075519
Kind:	fallback
Category:	legalize: G_LSHR <2 x s64>
Occurrences:	21 in 6 configs, 4 test files
Snippet from:	rvp-simd-64.ll @test_pasubu_w via llvm-extract
Config:	`-mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs`
Local check:	reproduces at bc8218b282
Compiler Explorer:	not uploaded (over --godbolt-limit or disabled)

Snippet:

define <2 x i32> @test_pasubu_w(<2 x i32> %a, <2 x i32> %b) {
  %a_ext = zext <2 x i32> %a to <2 x i64>
  %b_ext = zext <2 x i32> %b to <2 x i64>
  %sub = sub <2 x i64> %a_ext, %b_ext
  %res = lshr <2 x i64> %sub, splat (i64 1)
  %res_trunc = trunc <2 x i64> %res to <2 x i32>
  ret <2 x i32> %res_trunc
}

Reproduce:

llc -mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel.* snippet.ll -o -
llc -mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs -global-isel=0 snippet.ll -o -

Local llc output:

remark: <unknown>:0:0: unable to legalize instruction: %7:_(<2 x s64>) = G_LSHR %4:_, %5:_(<2 x s64>) (in function: test_pasubu_w)
warning: Instruction selection used fallback path for test_pasubu_w

Occurrences (21):

Input	Function	Config
rvp-simd-64.ll	test_pasubu_w	`-mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs`
rvp-simd-64.ll	test_pmulh_w	`-mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs`
rvp-simd-64.ll	test_pmulhu_w	`-mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs`
rvp-simd-64.ll	test_pmulhsu_w	`-mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs`
rvp-simd-64.ll	test_pmulhsu_w_commuted	`-mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs`
rvp-simd-64.ll	test_pmulhr_w	`-mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs`
rvp-simd-64.ll	test_pmulhru_w	`-mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs`
rvp-simd-64.ll	test_pmulhrsu_w	`-mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs`
rvp-simd-64.ll	test_pmulhrsu_w_commuted	`-mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs`
rvp-simd-64.ll	test_pmulhu_v2i32	`-mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs`
umulh.ll	umulh_v2i32	`-mtriple=riscv32 -mattr=+m`
umulh.ll	umulh_v2i32	`-mtriple=riscv64 -mattr=+m`
smulh.36e7bea6c1.ll (mutant of smulh.ll)	smulh_v2i64	`-mtriple=riscv64`
smulh.93c85f0468.ll (mutant of smulh.ll)	smulh_v2i64	`-mtriple=riscv32 -mattr=+m`
smulh.d54008bffc.ll (mutant of smulh.ll)	smulh_v2i64	`-mtriple=riscv64 -mattr=+m`
smulh.f578ab5712.ll (mutant of smulh.ll)	smulh_v2i64	`-mtriple=riscv32`
umulh.ab0efe761b.ll (mutant of umulh.ll)	umulh_v2i64	`-mtriple=riscv32 -mattr=+m`
umulh.b2157e4448.ll (mutant of umulh.ll)	umulh_v2i64	`-mtriple=riscv32`
umulh.bdd8f2b07d.ll (mutant of umulh.ll)	umulh_v2i64	`-mtriple=riscv64`
umulh.c02cf47744.ll (mutant of umulh.ll)	umulh_v2i64	`-mtriple=riscv64 -mattr=+m`
xqcilo-xqcilia-frame-index.009407688c.ll (mutant of xqcilo-xqcilia-frame-index.ll)	bare_fi_high_frame_store	`-mtriple=riscv32 -mattr=+xqcilo,+xqcilia -riscv-no-aliases`

Generated 2026-10-15 08:05 UTC.