[llvm] [Hexagon] Implement @llvm.readsteadycounter() (PR #93247)

[Brian Cain via llvm-commits]

https://github.com/androm3da created https://github.com/llvm/llvm-project/pull/93247

This commit was inspired by @kparzysz's ab57c2bad3dc ([Hexagon] Implement @llvm.readcyclecounter(), 2017-02-22)

>From a0fba4304effaa765110bbcbbcb8ecc360338ff8 Mon Sep 17 00:00:00 2001
From: Brian Cain <bcain at quicinc.com>
Date: Thu, 23 May 2024 14:29:55 -0700
Subject: [PATCH] [Hexagon] Implement @llvm.readsteadycounter()

This commit was inspired by @kparzysz's ab57c2bad3dc ([Hexagon] Implement
@llvm.readcyclecounter(), 2017-02-22)
---
 llvm/lib/Target/Hexagon/HexagonISelLowering.cpp | 15 +++++++++++++++
 llvm/lib/Target/Hexagon/HexagonISelLowering.h   |  2 ++
 llvm/lib/Target/Hexagon/HexagonPatterns.td      |  6 ++++++
 llvm/test/CodeGen/Hexagon/readsteadycounter.ll  | 11 +++++++++++
 4 files changed, 34 insertions(+)
 create mode 100644 llvm/test/CodeGen/Hexagon/readsteadycounter.ll

diff --git a/llvm/lib/Target/Hexagon/HexagonISelLowering.cpp b/llvm/lib/Target/Hexagon/HexagonISelLowering.cpp
index 41462cceef51d..22a88734afd44 100644
--- a/llvm/lib/Target/Hexagon/HexagonISelLowering.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonISelLowering.cpp
@@ -732,6 +732,18 @@ SDValue HexagonTargetLowering::LowerREADCYCLECOUNTER(SDValue Op,
   return DAG.getNode(HexagonISD::READCYCLE, dl, VTs, Chain);
 }
 
+// Custom-handle ISD::READSTEADYCOUNTER because the target-independent SDNode
+// is marked as having side-effects, while the register read on Hexagon does
+// not have any. TableGen refuses to accept the direct pattern from that node
+// to the A4_tfrcpp.
+SDValue HexagonTargetLowering::LowerREADSTEADYCOUNTER(SDValue Op,
+                                                      SelectionDAG &DAG) const {
+  SDValue Chain = Op.getOperand(0);
+  SDLoc dl(Op);
+  SDVTList VTs = DAG.getVTList(MVT::i64, MVT::Other);
+  return DAG.getNode(HexagonISD::READTIMER, dl, VTs, Chain);
+}
+
 SDValue HexagonTargetLowering::LowerINTRINSIC_VOID(SDValue Op,
       SelectionDAG &DAG) const {
   SDValue Chain = Op.getOperand(0);
@@ -1507,6 +1519,7 @@ HexagonTargetLowering::HexagonTargetLowering(const TargetMachine &TM,
   setOperationAction(ISD::INLINEASM_BR,         MVT::Other, Custom);
   setOperationAction(ISD::PREFETCH,             MVT::Other, Custom);
   setOperationAction(ISD::READCYCLECOUNTER,     MVT::i64,   Custom);
+  setOperationAction(ISD::READSTEADYCOUNTER,    MVT::i64,   Custom);
   setOperationAction(ISD::INTRINSIC_VOID,       MVT::Other, Custom);
   setOperationAction(ISD::EH_RETURN,            MVT::Other, Custom);
   setOperationAction(ISD::GLOBAL_OFFSET_TABLE,  MVT::i32,   Custom);
@@ -1932,6 +1945,7 @@ const char* HexagonTargetLowering::getTargetNodeName(unsigned Opcode) const {
   case HexagonISD::VINSERTW0:     return "HexagonISD::VINSERTW0";
   case HexagonISD::VROR:          return "HexagonISD::VROR";
   case HexagonISD::READCYCLE:     return "HexagonISD::READCYCLE";
+  case HexagonISD::READTIMER:     return "HexagonISD::READTIMER";
   case HexagonISD::PTRUE:         return "HexagonISD::PTRUE";
   case HexagonISD::PFALSE:        return "HexagonISD::PFALSE";
   case HexagonISD::D2P:           return "HexagonISD::D2P";
@@ -3389,6 +3403,7 @@ HexagonTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
     case ISD::INTRINSIC_VOID:       return LowerINTRINSIC_VOID(Op, DAG);
     case ISD::PREFETCH:             return LowerPREFETCH(Op, DAG);
     case ISD::READCYCLECOUNTER:     return LowerREADCYCLECOUNTER(Op, DAG);
+    case ISD::READSTEADYCOUNTER:    return LowerREADSTEADYCOUNTER(Op, DAG);
       break;
   }
 
diff --git a/llvm/lib/Target/Hexagon/HexagonISelLowering.h b/llvm/lib/Target/Hexagon/HexagonISelLowering.h
index 2ddbed0506399..3fd961f5a7462 100644
--- a/llvm/lib/Target/Hexagon/HexagonISelLowering.h
+++ b/llvm/lib/Target/Hexagon/HexagonISelLowering.h
@@ -77,6 +77,7 @@ enum NodeType : unsigned {
   EH_RETURN,
   DCFETCH,
   READCYCLE,
+  READTIMER,
   PTRUE,
   PFALSE,
   D2P,         // Convert 8-byte value to 8-bit predicate register. [*]
@@ -207,6 +208,7 @@ class HexagonTargetLowering : public TargetLowering {
   SDValue LowerFDIV(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerPREFETCH(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerREADCYCLECOUNTER(SDValue Op, SelectionDAG &DAG) const;
+  SDValue LowerREADSTEADYCOUNTER(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerEH_LABEL(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerEH_RETURN(SDValue Op, SelectionDAG &DAG) const;
   SDValue
diff --git a/llvm/lib/Target/Hexagon/HexagonPatterns.td b/llvm/lib/Target/Hexagon/HexagonPatterns.td
index ea7c4acd0e830..baa552fcd220d 100644
--- a/llvm/lib/Target/Hexagon/HexagonPatterns.td
+++ b/llvm/lib/Target/Hexagon/HexagonPatterns.td
@@ -3392,6 +3392,12 @@ def HexagonREADCYCLE: SDNode<"HexagonISD::READCYCLE", SDTInt64Leaf,
 
 def: Pat<(HexagonREADCYCLE), (A4_tfrcpp UPCYCLE)>;
 
+// Read time counter.
+def HexagonREADTIMER: SDNode<"HexagonISD::READTIMER", SDTInt64Leaf,
+  [SDNPHasChain]>;
+
+def: Pat<(HexagonREADTIMER), (A4_tfrcpp UTIMER)>;
+
 // The declared return value of the store-locked intrinsics is i32, but
 // the instructions actually define i1. To avoid register copies from
 // IntRegs to PredRegs and back, fold the entire pattern checking the
diff --git a/llvm/test/CodeGen/Hexagon/readsteadycounter.ll b/llvm/test/CodeGen/Hexagon/readsteadycounter.ll
new file mode 100644
index 0000000000000..5a78552117d9e
--- /dev/null
+++ b/llvm/test/CodeGen/Hexagon/readsteadycounter.ll
@@ -0,0 +1,11 @@
+
+; RUN: llc -march=hexagon < %s | FileCheck %s
+
+; CHECK-LABEL: test_readsteadycounter
+; CHECK: r1:0 = c31:30
+define i64 @test_readsteadycounter() nounwind {
+  %t0 = call i64 @llvm.readsteadycounter()
+  ret i64 %t0
+}
+
+declare i64 @llvm.readsteadycounter()