[llvm] [AArch64] Make use of byte FPR stores for bytes extracted from vectors (PR #134117)

[Benjamin Maxwell via llvm-commits]

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@@ -4589,6 +4589,18 @@ def : Pat<(truncstorei16 GPR64:$Rt, (am_unscaled16 GPR64sp:$Rn, simm9:$offset)),
 def : Pat<(truncstorei8 GPR64:$Rt, (am_unscaled8 GPR64sp:$Rn, simm9:$offset)),
   (STURBBi (EXTRACT_SUBREG GPR64:$Rt, sub_32), GPR64sp:$Rn, simm9:$offset)>;
 
+// v1i64 -> bsub truncating stores
+// Supporting pattern lower f32/64 -> v8i8
+def : Pat<(v8i8 (vector_insert (v8i8 (undef)), (i32 FPR32:$src), 0)),
+          (INSERT_SUBREG (v8i8 (IMPLICIT_DEF)), FPR32:$src, ssub)>;
+def : Pat<(v8i8 (vector_insert (v8i8 (undef)), (i64 FPR64:$src), 0)),
+          (v8i8 (EXTRACT_SUBREG (INSERT_SUBREG (v16i8 (IMPLICIT_DEF)), FPR64:$src, dsub), dsub))>;
+// Lower v1i64 -> v1i8 truncstore to bsub store
+def : Pat<(truncstorevi8 v1i64:$VT, (am_unscaled8 GPR64sp:$Rn, simm9:$offset)),
+          (STURBi (vi8 (EXTRACT_SUBREG v1i64:$VT, bsub)), GPR64sp:$Rn, simm9:$offset)>;
+def : Pat<(truncstorevi8 v1i64:$VT, (am_indexed8 GPR64sp:$Rn, uimm12s4:$offset)),
+          (STRBui (vi8 (EXTRACT_SUBREG v1i64:$VT, bsub)), GPR64sp:$Rn, uimm12s4:$offset)>;
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MacDue wrote:

Note: There are a bunch of other target-specific MVTs next to where I placed `vi8` (including some for AArch64), so I thought it was a reasonable, and fairly unobtrusive solution. 

https://github.com/llvm/llvm-project/pull/134117