[llvm] [X86] SimplifyDemandedVectorEltsForTargetNode - reduce width of X86 conversions nodes when upper elements are not demanded. (PR #102882)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon updated https://github.com/llvm/llvm-project/pull/102882

>From 441954ad925da5b676c4e9593fccc6d758091ae2 Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev at redking.me.uk>
Date: Mon, 12 Aug 2024 12:08:12 +0100
Subject: [PATCH 1/2] [X86] SimplifyDemandedVectorEltsForTargetNode - reduce
 width of X86 conversions nodes when upper elements are not demanded.

Fixes #83402
---
 llvm/lib/Target/X86/X86ISelLowering.cpp       | 19 +++++++++++++++++++
 .../CodeGen/X86/vector-half-conversions.ll    | 19 ++++++++-----------
 2 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index db50f132b1349f..24cbc8f93391e5 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -42524,6 +42524,25 @@ bool X86TargetLowering::SimplifyDemandedVectorEltsForTargetNode(
       SDValue Insert =
           insertSubVector(UndefVec, ExtOp, 0, TLO.DAG, DL, ExtSizeInBits);
       return TLO.CombineTo(Op, Insert);
+    }
+      // Conversions.
+    case X86ISD::CVTTP2SI:
+    case X86ISD::CVTTP2UI:
+    case X86ISD::CVTPH2PS: {
+      SDLoc DL(Op);
+      unsigned Scale = SizeInBits / ExtSizeInBits;
+      SDValue SrcOp = Op.getOperand(0);
+      MVT SrcVT = SrcOp.getSimpleValueType();
+      unsigned SrcExtSize =
+          std::max<unsigned>(SrcVT.getSizeInBits() / Scale, 128);
+      MVT ExtVT = MVT::getVectorVT(VT.getSimpleVT().getScalarType(),
+                                   ExtSizeInBits / VT.getScalarSizeInBits());
+      SDValue ExtOp = TLO.DAG.getNode(
+          Opc, DL, ExtVT, extractSubVector(SrcOp, 0, TLO.DAG, DL, SrcExtSize));
+      SDValue UndefVec = TLO.DAG.getUNDEF(VT);
+      SDValue Insert =
+          insertSubVector(UndefVec, ExtOp, 0, TLO.DAG, DL, ExtSizeInBits);
+      return TLO.CombineTo(Op, Insert);
     }
       // Zero upper elements.
     case X86ISD::VZEXT_MOVL:
diff --git a/llvm/test/CodeGen/X86/vector-half-conversions.ll b/llvm/test/CodeGen/X86/vector-half-conversions.ll
index e87814ebb1dbe4..ef0f3f3e816dfa 100644
--- a/llvm/test/CodeGen/X86/vector-half-conversions.ll
+++ b/llvm/test/CodeGen/X86/vector-half-conversions.ll
@@ -4990,6 +4990,7 @@ define <4 x i32> @fptosi_2f16_to_4i32(<2 x half> %a) nounwind {
   ret <4 x i32> %ext
 }
 
+; PR83402
 define <4 x i32> @fptosi_4f16_to_4i32(<4 x half> %a) nounwind {
 ; AVX-LABEL: fptosi_4f16_to_4i32:
 ; AVX:       # %bb.0:
@@ -5024,16 +5025,14 @@ define <4 x i32> @fptosi_4f16_to_4i32(<4 x half> %a) nounwind {
 ;
 ; F16C-LABEL: fptosi_4f16_to_4i32:
 ; F16C:       # %bb.0:
-; F16C-NEXT:    vcvtph2ps %xmm0, %ymm0
+; F16C-NEXT:    vcvtph2ps %xmm0, %xmm0
 ; F16C-NEXT:    vcvttps2dq %xmm0, %xmm0
-; F16C-NEXT:    vzeroupper
 ; F16C-NEXT:    retq
 ;
 ; AVX512-LABEL: fptosi_4f16_to_4i32:
 ; AVX512:       # %bb.0:
-; AVX512-NEXT:    vcvtph2ps %xmm0, %ymm0
+; AVX512-NEXT:    vcvtph2ps %xmm0, %xmm0
 ; AVX512-NEXT:    vcvttps2dq %xmm0, %xmm0
-; AVX512-NEXT:    vzeroupper
 ; AVX512-NEXT:    retq
   %cvt = fptosi <4 x half> %a to <4 x i32>
   ret <4 x i32> %cvt
@@ -5213,13 +5212,12 @@ define <4 x i32> @fptoui_4f16_to_4i32(<4 x half> %a) nounwind {
 ;
 ; F16C-LABEL: fptoui_4f16_to_4i32:
 ; F16C:       # %bb.0:
-; F16C-NEXT:    vcvtph2ps %xmm0, %ymm0
-; F16C-NEXT:    vcvttps2dq %ymm0, %ymm1
-; F16C-NEXT:    vsubps {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm0, %ymm0
-; F16C-NEXT:    vcvttps2dq %ymm0, %ymm0
+; F16C-NEXT:    vcvtph2ps %xmm0, %xmm0
+; F16C-NEXT:    vcvttps2dq %xmm0, %xmm1
+; F16C-NEXT:    vsubps {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0, %xmm0
+; F16C-NEXT:    vcvttps2dq %xmm0, %xmm0
 ; F16C-NEXT:    vorps %xmm0, %xmm1, %xmm0
 ; F16C-NEXT:    vblendvps %xmm1, %xmm0, %xmm1, %xmm0
-; F16C-NEXT:    vzeroupper
 ; F16C-NEXT:    retq
 ;
 ; AVX512F-LABEL: fptoui_4f16_to_4i32:
@@ -5232,9 +5230,8 @@ define <4 x i32> @fptoui_4f16_to_4i32(<4 x half> %a) nounwind {
 ;
 ; AVX512-FASTLANE-LABEL: fptoui_4f16_to_4i32:
 ; AVX512-FASTLANE:       # %bb.0:
-; AVX512-FASTLANE-NEXT:    vcvtph2ps %xmm0, %ymm0
+; AVX512-FASTLANE-NEXT:    vcvtph2ps %xmm0, %xmm0
 ; AVX512-FASTLANE-NEXT:    vcvttps2udq %xmm0, %xmm0
-; AVX512-FASTLANE-NEXT:    vzeroupper
 ; AVX512-FASTLANE-NEXT:    retq
   %cvt = fptoui <4 x half> %a to <4 x i32>
   ret <4 x i32> %cvt

>From f94dbe13604708bb094263cdb0fc0af5e39bd830 Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev at redking.me.uk>
Date: Mon, 12 Aug 2024 15:51:00 +0100
Subject: [PATCH 2/2] Add TODO comment to add additional conversion opcodes

---
 llvm/lib/Target/X86/X86ISelLowering.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 24cbc8f93391e5..c6e1764edffc3a 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -42526,6 +42526,7 @@ bool X86TargetLowering::SimplifyDemandedVectorEltsForTargetNode(
       return TLO.CombineTo(Op, Insert);
     }
       // Conversions.
+      // TODO: Add more CVT opcodes when we have test coverage.
     case X86ISD::CVTTP2SI:
     case X86ISD::CVTTP2UI:
     case X86ISD::CVTPH2PS: {