[LLVM][InstCombine][SVE] fcvtnt(a,all_active,b) != fcvtnt(undef,all_active,b) (#110278)

The "narrowing top" convert instructions leave the bottom half of active
elements untouched and thus the first paramater of their associated
intrinsic remains live even when there are no inactive lanes.

Author: paulwalker-arm

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -2166,11 +2166,7 @@ AArch64TTIImpl::instCombineIntrinsic(InstCombiner &IC,
   case Intrinsic::aarch64_sve_fcvt_f64f32:
   case Intrinsic::aarch64_sve_fcvtlt_f32f16:
   case Intrinsic::aarch64_sve_fcvtlt_f64f32:
-  case Intrinsic::aarch64_sve_fcvtnt_bf16f32:
-  case Intrinsic::aarch64_sve_fcvtnt_f16f32:
-  case Intrinsic::aarch64_sve_fcvtnt_f32f64:
   case Intrinsic::aarch64_sve_fcvtx_f32f64:
-  case Intrinsic::aarch64_sve_fcvtxnt_f32f64:
   case Intrinsic::aarch64_sve_fcvtzs:
   case Intrinsic::aarch64_sve_fcvtzs_i32f16:
   case Intrinsic::aarch64_sve_fcvtzs_i32f64:
@@ -2192,6 +2188,11 @@ AArch64TTIImpl::instCombineIntrinsic(InstCombiner &IC,
   case Intrinsic::aarch64_sve_ucvtf_f32i64:
   case Intrinsic::aarch64_sve_ucvtf_f64i32:
     return instCombineSVEAllOrNoActiveUnary(IC, II);
+  case Intrinsic::aarch64_sve_fcvtnt_bf16f32:
+  case Intrinsic::aarch64_sve_fcvtnt_f16f32:
+  case Intrinsic::aarch64_sve_fcvtnt_f32f64:
+  case Intrinsic::aarch64_sve_fcvtxnt_f32f64:
+    return instCombineSVENoActiveReplace(IC, II, true);
   case Intrinsic::aarch64_sve_st1_scatter:
   case Intrinsic::aarch64_sve_st1_scatter_scalar_offset:
   case Intrinsic::aarch64_sve_st1_scatter_sxtw:

llvm/test/Transforms/InstCombine/AArch64/sve-intrinsic-comb-all-active-lanes-cvt.ll

@@ -138,7 +138,7 @@ define <vscale x 8 x bfloat> @test_fcvtnt_bf16_f32(<vscale x 8 x bfloat> %a, <vs
 ; CHECK-LABEL: define <vscale x 8 x bfloat> @test_fcvtnt_bf16_f32(
 ; CHECK-SAME: <vscale x 8 x bfloat> [[A:%.*]], <vscale x 4 x float> [[B:%.*]]) {
 ; CHECK-NEXT:    [[PG:%.*]] = tail call <vscale x 8 x i1> @llvm.aarch64.sve.ptrue.nxv8i1(i32 31)
-; CHECK-NEXT:    [[OUT:%.*]] = call <vscale x 8 x bfloat> @llvm.aarch64.sve.fcvtnt.bf16f32(<vscale x 8 x bfloat> undef, <vscale x 8 x i1> [[PG]], <vscale x 4 x float> [[B]])
+; CHECK-NEXT:    [[OUT:%.*]] = call <vscale x 8 x bfloat> @llvm.aarch64.sve.fcvtnt.bf16f32(<vscale x 8 x bfloat> [[A]], <vscale x 8 x i1> [[PG]], <vscale x 4 x float> [[B]])
 ; CHECK-NEXT:    ret <vscale x 8 x bfloat> [[OUT]]
 ;
   %pg = tail call <vscale x 8 x i1> @llvm.aarch64.sve.ptrue.nxv8i1(i32 31)
@@ -150,7 +150,7 @@ define <vscale x 8 x half> @test_fcvtnt_f16_f32(<vscale x 8 x half> %a, <vscale
 ; CHECK-LABEL: define <vscale x 8 x half> @test_fcvtnt_f16_f32(
 ; CHECK-SAME: <vscale x 8 x half> [[A:%.*]], <vscale x 4 x float> [[B:%.*]]) {
 ; CHECK-NEXT:    [[PG:%.*]] = tail call <vscale x 4 x i1> @llvm.aarch64.sve.ptrue.nxv4i1(i32 31)
-; CHECK-NEXT:    [[OUT:%.*]] = call <vscale x 8 x half> @llvm.aarch64.sve.fcvtnt.f16f32(<vscale x 8 x half> undef, <vscale x 4 x i1> [[PG]], <vscale x 4 x float> [[B]])
+; CHECK-NEXT:    [[OUT:%.*]] = call <vscale x 8 x half> @llvm.aarch64.sve.fcvtnt.f16f32(<vscale x 8 x half> [[A]], <vscale x 4 x i1> [[PG]], <vscale x 4 x float> [[B]])
 ; CHECK-NEXT:    ret <vscale x 8 x half> [[OUT]]
 ;
   %pg = tail call <vscale x 4 x i1> @llvm.aarch64.sve.ptrue.nxv4i1(i32 31)
@@ -162,7 +162,7 @@ define <vscale x 4 x float> @test_fcvtnt_f32_f64(<vscale x 4 x float> %a, <vscal
 ; CHECK-LABEL: define <vscale x 4 x float> @test_fcvtnt_f32_f64(
 ; CHECK-SAME: <vscale x 4 x float> [[A:%.*]], <vscale x 2 x double> [[B:%.*]]) {
 ; CHECK-NEXT:    [[PG:%.*]] = tail call <vscale x 2 x i1> @llvm.aarch64.sve.ptrue.nxv2i1(i32 31)
-; CHECK-NEXT:    [[OUT:%.*]] = call <vscale x 4 x float> @llvm.aarch64.sve.fcvtnt.f32f64(<vscale x 4 x float> undef, <vscale x 2 x i1> [[PG]], <vscale x 2 x double> [[B]])
+; CHECK-NEXT:    [[OUT:%.*]] = call <vscale x 4 x float> @llvm.aarch64.sve.fcvtnt.f32f64(<vscale x 4 x float> [[A]], <vscale x 2 x i1> [[PG]], <vscale x 2 x double> [[B]])
 ; CHECK-NEXT:    ret <vscale x 4 x float> [[OUT]]
 ;
   %pg = tail call <vscale x 2 x i1> @llvm.aarch64.sve.ptrue.nxv2i1(i32 31)
@@ -186,7 +186,7 @@ define <vscale x 4 x float> @test_fcvtxnt_f32_f64(<vscale x 4 x float> %a, <vsca
 ; CHECK-LABEL: define <vscale x 4 x float> @test_fcvtxnt_f32_f64(
 ; CHECK-SAME: <vscale x 4 x float> [[A:%.*]], <vscale x 2 x double> [[B:%.*]]) {
 ; CHECK-NEXT:    [[PG:%.*]] = tail call <vscale x 2 x i1> @llvm.aarch64.sve.ptrue.nxv2i1(i32 31)
-; CHECK-NEXT:    [[OUT:%.*]] = call <vscale x 4 x float> @llvm.aarch64.sve.fcvtxnt.f32f64(<vscale x 4 x float> undef, <vscale x 2 x i1> [[PG]], <vscale x 2 x double> [[B]])
+; CHECK-NEXT:    [[OUT:%.*]] = call <vscale x 4 x float> @llvm.aarch64.sve.fcvtxnt.f32f64(<vscale x 4 x float> [[A]], <vscale x 2 x i1> [[PG]], <vscale x 2 x double> [[B]])
 ; CHECK-NEXT:    ret <vscale x 4 x float> [[OUT]]
 ;
   %pg = tail call <vscale x 2 x i1> @llvm.aarch64.sve.ptrue.nxv2i1(i32 31)