optimize is_finite on floating points

Author: folkertdev

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -9122,8 +9122,16 @@ SDValue TargetLowering::expandIS_FPCLASS(EVT ResultVT, SDValue Op,
     ; // Detect finite numbers of f80 by checking individual classes because
       // they have different settings of the explicit integer bit.
   else if ((Test & fcFinite) == fcFinite) {
-    // finite(V) ==> abs(V) < exp_mask
-    PartialRes = DAG.getSetCC(DL, ResultVT, AbsV, ExpMaskV, ISD::SETLT);
+    // Float arithmetic may emit FP exceptions.
+    if (Flags.hasNoFPExcept()) {
+      // finite(V) ==> (V - V) == (V - V)
+      SDValue Sub = DAG.getNode(ISD::FSUB, DL, OperandVT, Op, Op);
+      SDValue Zero = DAG.getConstantFP(0.0, DL, OperandVT);
+      PartialRes = DAG.getSetCC(DL, ResultVT, Sub, Zero, ISD::SETO);
+    } else {
+      // finite(V) ==> abs(V) < exp_mask
+      PartialRes = DAG.getSetCC(DL, ResultVT, AbsV, ExpMaskV, ISD::SETLT);
+    }
     Test &= ~fcFinite;
   } else if ((Test & fcFinite) == fcPosFinite) {
     // finite(V) && V > 0 ==> V < exp_mask

llvm/test/CodeGen/AArch64/is_fpclass.ll

@@ -0,0 +1,49 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=aarch64 -verify-machineinstrs %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-SD
+; RUN: llc -mtriple=aarch64 -global-isel -verify-machineinstrs %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-GI
+
+define i1 @isfinite_f(float %x) {
+; CHECK-SD-LABEL: isfinite_f:
+; CHECK-SD:       // %bb.0: // %entry
+; CHECK-SD-NEXT:    fsub s0, s0, s0
+; CHECK-SD-NEXT:    fcmp s0, s0
+; CHECK-SD-NEXT:    cset w0, vc
+; CHECK-SD-NEXT:    ret
+;
+; CHECK-GI-LABEL: isfinite_f:
+; CHECK-GI:       // %bb.0: // %entry
+; CHECK-GI-NEXT:    fmov w9, s0
+; CHECK-GI-NEXT:    mov w8, #2139095040 // =0x7f800000
+; CHECK-GI-NEXT:    and w9, w9, #0x7fffffff
+; CHECK-GI-NEXT:    cmp w9, w8
+; CHECK-GI-NEXT:    cset w0, lo
+; CHECK-GI-NEXT:    ret
+entry:
+  %0 = tail call i1 @llvm.is.fpclass.f32(float %x, i32 504)  ; 0x1f8 = "finite"
+  ret i1 %0
+}
+
+define i1 @not_isfinite_f(float %x) {
+; CHECK-SD-LABEL: not_isfinite_f:
+; CHECK-SD:       // %bb.0: // %entry
+; CHECK-SD-NEXT:    fsub s0, s0, s0
+; CHECK-SD-NEXT:    fcmp s0, s0
+; CHECK-SD-NEXT:    cset w0, vs
+; CHECK-SD-NEXT:    ret
+;
+; CHECK-GI-LABEL: not_isfinite_f:
+; CHECK-GI:       // %bb.0: // %entry
+; CHECK-GI-NEXT:    fmov w9, s0
+; CHECK-GI-NEXT:    mov w8, #2139095040 // =0x7f800000
+; CHECK-GI-NEXT:    and w9, w9, #0x7fffffff
+; CHECK-GI-NEXT:    cmp w9, w8
+; CHECK-GI-NEXT:    cset w8, eq
+; CHECK-GI-NEXT:    cset w9, hi
+; CHECK-GI-NEXT:    orr w0, w8, w9
+; CHECK-GI-NEXT:    ret
+entry:
+  %0 = tail call i1 @llvm.is.fpclass.f32(float %x, i32 519)  ; ~0x1f8 = "~finite"
+  ret i1 %0
+}
+;; NOTE: These prefixes are unused and the list is autogenerated. Do not add tests below this line:
+; CHECK: {{.*}}