[LoongArch] Support floating-point number reciprocal

llvm/lib/Target/LoongArch/LoongArchFloat32InstrInfo.td

 /// Floating point constants
 
 def : Pat<(f32 fpimm0), (MOVGR2FR_W R0)>;
 def : Pat<(f32 fpimm0neg), (FNEG_S (MOVGR2FR_W R0))>;
 def : Pat<(f32 fpimm1), (FFINT_S_W (MOVGR2FR_W (ADDI_W R0, 1)))>;
 
 // FP Conversion
 def : Pat<(loongarch_ftint FPR32:$src), (FTINTRZ_W_S FPR32:$src)>;
+
+// FP reciprocal operation
+def : Pat<(fdiv fpimm1, FPR32:$src), (FRECIP_S $src)>;
 } // Predicates = [HasBasicF]
 
 let Predicates = [HasBasicF, IsLA64] in {
 // GPR -> FPR
 def : Pat<(loongarch_movgr2fr_w_la64 GPR:$src), (MOVGR2FR_W GPR:$src)>;
 // FPR -> GPR
 def : Pat<(loongarch_movfr2gr_s_la64 FPR32:$src),
           (MOVFR2GR_S FPR32:$src)>;

llvm/lib/Target/LoongArch/LoongArchFloat64InstrInfo.td

 def : Pat<(loongarch_ftint FPR64:$src), (FTINTRZ_W_D FPR64:$src)>;
 def : Pat<(f64 (loongarch_ftint FPR64:$src)), (FTINTRZ_L_D FPR64:$src)>;
 def : Pat<(loongarch_ftint FPR32:$src), (FTINTRZ_L_S FPR32:$src)>;
 
 // f64 -> f32
 def : Pat<(f32 (fpround FPR64:$src)), (FCVT_S_D FPR64:$src)>;
 // f32 -> f64
 def : Pat<(f64 (fpextend FPR32:$src)), (FCVT_D_S FPR32:$src)>;
+
+// FP reciprocal operation
+def : Pat<(fdiv fpimm1, FPR64:$src), (FRECIP_D $src)>;
 } // Predicates = [HasBasicD]
 
 /// Floating point constants
 
 let Predicates = [HasBasicD, IsLA64] in {
 def : Pat<(f64 fpimm0), (MOVGR2FR_D R0)>;
 def : Pat<(f64 fpimm0neg), (FNEG_D (MOVGR2FR_D R0))>;
 def : Pat<(f64 fpimm1), (FFINT_D_L (MOVGR2FR_D (ADDI_D R0, 1)))>;

llvm/test/CodeGen/LoongArch/fp-reciprocal.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc --mtriple=loongarch32 --mattr=+f,-d < %s | FileCheck %s --check-prefix=LA32F
+; RUN: llc --mtriple=loongarch32 --mattr=+d < %s | FileCheck %s --check-prefix=LA32D
+; RUN: llc --mtriple=loongarch64 --mattr=+f,-d < %s | FileCheck %s --check-prefix=LA64F
+; RUN: llc --mtriple=loongarch64 --mattr=+d < %s | FileCheck %s --check-prefix=LA64D
+
+
+define float @f32_reciprocal(float %a) nounwind {
+; LA32F-LABEL: f32_reciprocal:
+; LA32F:       # %bb.0:
+; LA32F-NEXT:    frecip.s $fa0, $fa0
+; LA32F-NEXT:    ret
+;
+; LA32D-LABEL: f32_reciprocal:
+; LA32D:       # %bb.0:
+; LA32D-NEXT:    frecip.s $fa0, $fa0
+; LA32D-NEXT:    ret
+;
+; LA64F-LABEL: f32_reciprocal:
+; LA64F:       # %bb.0:
+; LA64F-NEXT:    frecip.s $fa0, $fa0
+; LA64F-NEXT:    ret
+;
+; LA64D-LABEL: f32_reciprocal:
+; LA64D:       # %bb.0:
+; LA64D-NEXT:    frecip.s $fa0, $fa0
+; LA64D-NEXT:    ret
+  %1 = fdiv float 1.0, %a
+  ret float %1
+}
+
+define double @f64_reciprocal(double %a) nounwind {
+; LA32F-LABEL: f64_reciprocal:
+; LA32F:       # %bb.0:
+; LA32F-NEXT:    addi.w $sp, $sp, -16
+; LA32F-NEXT:    st.w $ra, $sp, 12 # 4-byte Folded Spill
+; LA32F-NEXT:    move $a3, $a1
+; LA32F-NEXT:    move $a2, $a0
+; LA32F-NEXT:    lu12i.w $a1, 261888
+; LA32F-NEXT:    move $a0, $zero
+; LA32F-NEXT:    bl %plt(__divdf3)
+; LA32F-NEXT:    ld.w $ra, $sp, 12 # 4-byte Folded Reload
+; LA32F-NEXT:    addi.w $sp, $sp, 16
+; LA32F-NEXT:    ret
+;
+; LA32D-LABEL: f64_reciprocal:
+; LA32D:       # %bb.0:
+; LA32D-NEXT:    frecip.d $fa0, $fa0
+; LA32D-NEXT:    ret
+;
+; LA64F-LABEL: f64_reciprocal:
+; LA64F:       # %bb.0:
+; LA64F-NEXT:    addi.d $sp, $sp, -16
+; LA64F-NEXT:    st.d $ra, $sp, 8 # 8-byte Folded Spill
+; LA64F-NEXT:    move $a1, $a0
+; LA64F-NEXT:    lu52i.d $a0, $zero, 1023
+; LA64F-NEXT:    bl %plt(__divdf3)
+; LA64F-NEXT:    ld.d $ra, $sp, 8 # 8-byte Folded Reload
+; LA64F-NEXT:    addi.d $sp, $sp, 16
+; LA64F-NEXT:    ret
+;
+; LA64D-LABEL: f64_reciprocal:
+; LA64D:       # %bb.0:
+; LA64D-NEXT:    frecip.d $fa0, $fa0
+; LA64D-NEXT:    ret
+  %1 = fdiv double 1.0, %a
+  ret double %1
+}