[llvm] [HEXAGON] Add support to lower "FREEZE a half(f16)" instruction on (PR #130977)

[Abinaya Saravanan via llvm-commits]

https://github.com/quic-asaravan created https://github.com/llvm/llvm-project/pull/130977

Hexagon and fix the isel-buildvector-v2f16.ll assertion

>From 0822c10caa3497f5f98a7e11f79ca1ea3c38e177 Mon Sep 17 00:00:00 2001
From: quic-asaravan <quic_asaravan at quicinc.com>
Date: Wed, 12 Mar 2025 08:10:34 -0700
Subject: [PATCH] [HEXAGON] Add support to lower "FREEZE a half(f16)"
 instruction on Hexagon and fix the isel-buildvector-v2f16.ll assertion

---
 llvm/lib/Target/Hexagon/HexagonISelLowering.h |  1 +
 .../Target/Hexagon/HexagonISelLoweringHVX.cpp | 22 +++++-----
 llvm/test/CodeGen/Hexagon/fp16-promote.ll     | 44 +++++++++++++++++++
 3 files changed, 56 insertions(+), 11 deletions(-)
 create mode 100644 llvm/test/CodeGen/Hexagon/fp16-promote.ll

diff --git a/llvm/lib/Target/Hexagon/HexagonISelLowering.h b/llvm/lib/Target/Hexagon/HexagonISelLowering.h
index aaa9c65c1e07e..4df88b3a8abd7 100644
--- a/llvm/lib/Target/Hexagon/HexagonISelLowering.h
+++ b/llvm/lib/Target/Hexagon/HexagonISelLowering.h
@@ -362,6 +362,7 @@ class HexagonTargetLowering : public TargetLowering {
   shouldExpandAtomicRMWInIR(AtomicRMWInst *AI) const override {
     return AtomicExpansionKind::LLSC;
   }
+  bool softPromoteHalfType() const override { return true; }
 
 private:
   void initializeHVXLowering();
diff --git a/llvm/lib/Target/Hexagon/HexagonISelLoweringHVX.cpp b/llvm/lib/Target/Hexagon/HexagonISelLoweringHVX.cpp
index f77bda3138354..de2bac6905530 100644
--- a/llvm/lib/Target/Hexagon/HexagonISelLoweringHVX.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonISelLoweringHVX.cpp
@@ -1618,17 +1618,6 @@ HexagonTargetLowering::LowerHvxBuildVector(SDValue Op, SelectionDAG &DAG)
   for (unsigned i = 0; i != Size; ++i)
     Ops.push_back(Op.getOperand(i));
 
-  // First, split the BUILD_VECTOR for vector pairs. We could generate
-  // some pairs directly (via splat), but splats should be generated
-  // by the combiner prior to getting here.
-  if (VecTy.getSizeInBits() == 16*Subtarget.getVectorLength()) {
-    ArrayRef<SDValue> A(Ops);
-    MVT SingleTy = typeSplit(VecTy).first;
-    SDValue V0 = buildHvxVectorReg(A.take_front(Size/2), dl, SingleTy, DAG);
-    SDValue V1 = buildHvxVectorReg(A.drop_front(Size/2), dl, SingleTy, DAG);
-    return DAG.getNode(ISD::CONCAT_VECTORS, dl, VecTy, V0, V1);
-  }
-
   if (VecTy.getVectorElementType() == MVT::i1)
     return buildHvxVectorPred(Ops, dl, VecTy, DAG);
 
@@ -1645,6 +1634,17 @@ HexagonTargetLowering::LowerHvxBuildVector(SDValue Op, SelectionDAG &DAG)
     return DAG.getBitcast(tyVector(VecTy, MVT::f16), T0);
   }
 
+  // First, split the BUILD_VECTOR for vector pairs. We could generate
+  // some pairs directly (via splat), but splats should be generated
+  // by the combiner prior to getting here.
+  if (VecTy.getSizeInBits() == 16 * Subtarget.getVectorLength()) {
+    ArrayRef<SDValue> A(Ops);
+    MVT SingleTy = typeSplit(VecTy).first;
+    SDValue V0 = buildHvxVectorReg(A.take_front(Size / 2), dl, SingleTy, DAG);
+    SDValue V1 = buildHvxVectorReg(A.drop_front(Size / 2), dl, SingleTy, DAG);
+    return DAG.getNode(ISD::CONCAT_VECTORS, dl, VecTy, V0, V1);
+  }
+
   return buildHvxVectorReg(Ops, dl, VecTy, DAG);
 }
 
diff --git a/llvm/test/CodeGen/Hexagon/fp16-promote.ll b/llvm/test/CodeGen/Hexagon/fp16-promote.ll
new file mode 100644
index 0000000000000..1ef0a133ce30a
--- /dev/null
+++ b/llvm/test/CodeGen/Hexagon/fp16-promote.ll
@@ -0,0 +1,44 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -march=hexagon  < %s | FileCheck %s
+
+define half @freeze_half_undef() nounwind {
+; CHECK-LABEL: freeze_half_undef:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    {
+; CHECK-NEXT:     call __truncsfhf2
+; CHECK-NEXT:     r0 = #0
+; CHECK-NEXT:     allocframe(#0)
+; CHECK-NEXT:    }
+; CHECK-NEXT:    {
+; CHECK-NEXT:     call __extendhfsf2
+; CHECK-NEXT:    }
+; CHECK-NEXT:    {
+; CHECK-NEXT:     call __truncsfhf2
+; CHECK-NEXT:     r0 = sfadd(r0,r0)
+; CHECK-NEXT:    }
+; CHECK-NEXT:    {
+; CHECK-NEXT:     r31:30 = dealloc_return(r30):raw
+; CHECK-NEXT:    }
+  %y1 = freeze half undef
+  %t1 = fadd half %y1, %y1
+  ret half %t1
+}
+
+define half @freeze_half_poison(half %maybe.poison) {
+; CHECK-LABEL: freeze_half_poison:
+; CHECK:  // %bb.0:
+; CHECK:    {
+; CHECK-NEXT:     call __extendhfsf2
+; CHECK-NEXT:     allocframe(r29,#0):raw
+; CHECK-NEXT:    }
+; CHECK-NEXT:    {
+; CHECK-NEXT:     call __truncsfhf2
+; CHECK-NEXT:     r0 = sfadd(r0,r0)
+; CHECK-NEXT:    }
+; CHECK-NEXT:    {
+; CHECK-NEXT:     r31:30 = dealloc_return(r30):raw
+; CHECK-NEXT:    }
+  %y1 = freeze half %maybe.poison
+  %t1 = fadd half %y1, %y1
+  ret half %t1
+}