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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Paul Walker (paulwalker-arm)

<details>
<summary>Changes</summary>

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.

---
Full diff: https://github.com/llvm/llvm-project/pull/110278.diff


2 Files Affected:

- (modified) llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp (+5-4) 
- (modified) llvm/test/Transforms/InstCombine/AArch64/sve-intrinsic-comb-all-active-lanes-cvt.ll (+4-4) 


``````````diff
diff --git a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
index da0798ebf79578..4be236a7827f94 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -2156,11 +2156,7 @@ 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:
@@ -2182,6 +2178,11 @@ 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:
diff --git a/llvm/test/Transforms/InstCombine/AArch64/sve-intrinsic-comb-all-active-lanes-cvt.ll b/llvm/test/Transforms/InstCombine/AArch64/sve-intrinsic-comb-all-active-lanes-cvt.ll
index 374a9851917685..04550156be30be 100644
--- a/llvm/test/Transforms/InstCombine/AArch64/sve-intrinsic-comb-all-active-lanes-cvt.ll
+++ b/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)

``````````

</details>


https://github.com/llvm/llvm-project/pull/110278