[DAG] Implement generic llvm.canonicalize.f(16|32|64|128).

Previously, this expansion for the intrinsic has been implemented in the X86
backend. As suggested in the comments for the PR that merges that
implementation (#106370), this commit replicates that implementation (at least
for `f(16|32|64|128)`) in common code.

Canonicalization is thus implemented here as multiplication with 1.0.

This commit also touches the following backends: AArch64, AMDGPU, Mips,
PowerPC, and LoongArch. These backends previously added their own legalization
for `ISD::FCANONICALIZE`, but did not set the OperationAction accordingly,
since there was no default OperationAction in common code. Thus, this commit
adds the required `setOperationAction` calls and is otherwise intended as NFC
for these backends.

Author: dominik-steenken

llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

@@ -3356,6 +3356,32 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
     Results.push_back(Op);
     break;
   }
+  case ISD::FCANONICALIZE: {
+    // This implements llvm.canonicalize.f* by multiplication with 1.0, as
+    // suggested in
+    // https://llvm.org/docs/LangRef.html#llvm-canonicalize-intrinsic.
+    // It uses strict_fp operations even outside a strict_fp context in order
+    // to guarantee that the canonicalization is not optimized away by later
+    // passes. The result chain introduced by that is intentionally ignored
+    // since no ordering requirement is intended here.
+
+    // Create strict multiplication by 1.0.
+    SDValue Operand = Node->getOperand(0);
+    EVT VT = Operand.getValueType();
+    SDValue One = DAG.getConstantFP(1.0, dl, VT);
+    SDValue Chain = DAG.getEntryNode();
+    SDValue Mul = DAG.getNode(ISD::STRICT_FMUL, dl, {VT, MVT::Other},
+                              {Chain, Operand, One});
+
+    // Propagate existing flags on canonicalize, and additionally set
+    // NoFPExcept.
+    SDNodeFlags CanonicalizeFlags = Node->getFlags();
+    CanonicalizeFlags.setNoFPExcept(true);
+    Mul->setFlags(CanonicalizeFlags);
+
+    Results.push_back(Mul);
+    break;
+  }
   case ISD::SIGN_EXTEND_INREG: {
     EVT ExtraVT = cast<VTSDNode>(Node->getOperand(1))->getVT();
     EVT VT = Node->getValueType(0);

llvm/lib/CodeGen/TargetLoweringBase.cpp

@@ -871,6 +871,10 @@ void TargetLoweringBase::initActions() {
                       ISD::FATAN2},
                      {MVT::f32, MVT::f64, MVT::f128}, Expand);
 
+  // Insert custom handling default for llvm.canonicalize.*.
+  setOperationAction(ISD::FCANONICALIZE,
+                     {MVT::f16, MVT::f32, MVT::f64, MVT::f128}, Expand);
+
   // FIXME: Query RuntimeLibCalls to make the decision.
   setOperationAction({ISD::LRINT, ISD::LLRINT, ISD::LROUND, ISD::LLROUND},
                      {MVT::f32, MVT::f64, MVT::f128}, LibCall);

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -768,6 +768,12 @@ AArch64TargetLowering::AArch64TargetLowering(const TargetMachine &TM,
     setOperationAction(Op, MVT::v8bf16, Expand);
   }
 
+  // Legalize fcanonicalize to circumvent default expansion
+  setOperationAction(ISD::FCANONICALIZE, {MVT::f32, MVT::f64}, Legal);
+  if (Subtarget->hasFullFP16()) {
+    setOperationAction(ISD::FCANONICALIZE, MVT::f16, Legal);
+  }
+
   // fpextend from f16 or bf16 to f32 is legal
   setOperationAction(ISD::FP_EXTEND, MVT::f32, Legal);
   setOperationAction(ISD::FP_EXTEND, MVT::v4f32, Legal);

llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp

@@ -423,6 +423,11 @@ AMDGPUTargetLowering::AMDGPUTargetLowering(const TargetMachine &TM,
   setOperationAction({ISD::FLOG10, ISD::FLOG, ISD::FEXP, ISD::FEXP10}, MVT::f16,
                      Custom);
 
+  setOperationAction(ISD::FCANONICALIZE, {MVT::f32, MVT::f64}, Legal);
+  if (Subtarget->has16BitInsts()) {
+    setOperationAction(ISD::FCANONICALIZE, MVT::f16, Legal);
+  }
+
   // FIXME: These IS_FPCLASS vector fp types are marked custom so it reaches
   // scalarization code. Can be removed when IS_FPCLASS expand isn't called by
   // default unless marked custom/legal.

llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp

@@ -195,6 +195,7 @@ LoongArchTargetLowering::LoongArchTargetLowering(const TargetMachine &TM,
     setOperationAction(ISD::FMINNUM, MVT::f32, Legal);
     setOperationAction(ISD::FMAXNUM_IEEE, MVT::f32, Legal);
     setOperationAction(ISD::FMAXNUM, MVT::f32, Legal);
+    setOperationAction(ISD::FCANONICALIZE, MVT::f32, Legal);
     setOperationAction(ISD::STRICT_FSETCCS, MVT::f32, Legal);
     setOperationAction(ISD::STRICT_FSETCC, MVT::f32, Legal);
     setOperationAction(ISD::IS_FPCLASS, MVT::f32, Legal);
@@ -242,6 +243,7 @@ LoongArchTargetLowering::LoongArchTargetLowering(const TargetMachine &TM,
     setOperationAction(ISD::FMINNUM_IEEE, MVT::f64, Legal);
     setOperationAction(ISD::FMINNUM, MVT::f64, Legal);
     setOperationAction(ISD::FMAXNUM_IEEE, MVT::f64, Legal);
+    setOperationAction(ISD::FCANONICALIZE, MVT::f64, Legal);
     setOperationAction(ISD::FMAXNUM, MVT::f64, Legal);
     setOperationAction(ISD::IS_FPCLASS, MVT::f64, Legal);
     setOperationAction(ISD::FSIN, MVT::f64, Expand);

llvm/lib/Target/Mips/MipsISelLowering.cpp

@@ -373,6 +373,8 @@ MipsTargetLowering::MipsTargetLowering(const MipsTargetMachine &TM,
     setOperationAction(ISD::FMAXNUM, MVT::f64, Legal);
     setOperationAction(ISD::IS_FPCLASS, MVT::f32, Legal);
     setOperationAction(ISD::IS_FPCLASS, MVT::f64, Legal);
+    setOperationAction(ISD::FCANONICALIZE, MVT::f32, Legal);
+    setOperationAction(ISD::FCANONICALIZE, MVT::f64, Legal);
   } else {
     setOperationAction(ISD::FCANONICALIZE, MVT::f32, Custom);
     setOperationAction(ISD::FCANONICALIZE, MVT::f64, Custom);

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

@@ -777,6 +777,8 @@ PPCTargetLowering::PPCTargetLowering(const PPCTargetMachine &TM,
     setOperationAction(ISD::FMAXNUM_IEEE, MVT::f32, Legal);
     setOperationAction(ISD::FMINNUM_IEEE, MVT::f64, Legal);
     setOperationAction(ISD::FMINNUM_IEEE, MVT::f32, Legal);
+    setOperationAction(ISD::FCANONICALIZE, MVT::f64, Legal);
+    setOperationAction(ISD::FCANONICALIZE, MVT::f32, Legal);
   }
 
   if (Subtarget.hasAltivec()) {