Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -4161,26 +4161,31 @@
     return;
   }
 
-  const Operator *Op = dyn_cast<Operator>(V);
-  if (!Op)
-    return;
-
   FPClassTest KnownNotFromFlags = fcNone;
-  if (const FPMathOperator *FPOp = dyn_cast<FPMathOperator>(Op)) {
+  if (const auto *CB = dyn_cast<CallBase>(V))
+    KnownNotFromFlags |= CB->getRetNoFPClass();
+  else if (const auto *Arg = dyn_cast<Argument>(V))
+    KnownNotFromFlags |= Arg->getNoFPClass();
+
+  const Operator *Op = dyn_cast<Operator>(V);
+  if (const FPMathOperator *FPOp = dyn_cast_or_null<FPMathOperator>(Op)) {
     if (FPOp->hasNoNaNs())
       KnownNotFromFlags |= fcNan;
     if (FPOp->hasNoInfs())
       KnownNotFromFlags |= fcInf;
-
-    // We no longer need to find out about these bits from inputs if we can
-    // assume this from flags.
-    InterestedClasses = InterestedClasses & ~KnownNotFromFlags & fcAllFlags;
   }
 
+  // We no longer need to find out about these bits from inputs if we can
+  // assume this from flags/attributes.
+  InterestedClasses &= ~KnownNotFromFlags & fcAllFlags;
+
   auto ClearClassesFromFlags = make_scope_exit([=, &Known] {
     Known.knownNot(KnownNotFromFlags);
   });
 
+  if (!Op)
+    return;
+
   // All recursive calls that increase depth must come after this.
   if (Depth == MaxAnalysisRecursionDepth)
     return;
Index: llvm/unittests/Analysis/ValueTrackingTest.cpp
===================================================================
--- llvm/unittests/Analysis/ValueTrackingTest.cpp
+++ llvm/unittests/Analysis/ValueTrackingTest.cpp
@@ -1354,6 +1354,83 @@
   expectKnownFPClass(~(fcNan | fcInf) & fcAllFlags, std::nullopt);
 }
 
+TEST_F(ComputeKnownFPClassTest, SelectNoFPClassArgUnionAll) {
+  parseAssembly(
+      "define float @test(i1 %cond, float nofpclass(snan ninf nsub pzero pnorm) %arg0, float nofpclass(qnan nnorm nzero psub pinf) %arg1) {\n"
+      "  %A = select i1 %cond, float %arg0, float %arg1"
+      "  ret float %A\n"
+      "}\n");
+  expectKnownFPClass(fcAllFlags, std::nullopt);
+}
+
+TEST_F(ComputeKnownFPClassTest, SelectNoFPClassArgNoNan) {
+  parseAssembly(
+      "define float @test(i1 %cond, float nofpclass(nan) %arg0, float nofpclass(nan) %arg1) {\n"
+      "  %A = select i1 %cond, float %arg0, float %arg1"
+      "  ret float %A\n"
+      "}\n");
+  expectKnownFPClass(~fcNan & fcAllFlags, std::nullopt);
+}
+
+TEST_F(ComputeKnownFPClassTest, SelectNoFPClassArgNoPInf) {
+  parseAssembly(
+      "define float @test(i1 %cond, float nofpclass(inf) %arg0, float nofpclass(pinf) %arg1) {\n"
+      "  %A = select i1 %cond, float %arg0, float %arg1"
+      "  ret float %A\n"
+      "}\n");
+  expectKnownFPClass(~fcPosInf & fcAllFlags, std::nullopt);
+}
+
+TEST_F(ComputeKnownFPClassTest, SelectNoFPClassArgNoNInf) {
+  parseAssembly(
+      "define float @test(i1 %cond, float nofpclass(ninf) %arg0, float nofpclass(inf) %arg1) {\n"
+      "  %A = select i1 %cond, float %arg0, float %arg1"
+      "  ret float %A\n"
+      "}\n");
+  expectKnownFPClass(~fcNegInf & fcAllFlags, std::nullopt);
+}
+
+TEST_F(ComputeKnownFPClassTest, SelectNoFPClassCallSiteNoNan) {
+  parseAssembly(
+      "declare float @func()\n"
+      "define float @test() {\n"
+      "  %A = call nofpclass(nan) float @func()\n"
+      "  ret float %A\n"
+      "}\n");
+  expectKnownFPClass(~fcNan & fcAllFlags, std::nullopt);
+}
+
+TEST_F(ComputeKnownFPClassTest, SelectNoFPClassCallSiteNoZeros) {
+  parseAssembly(
+      "declare float @func()\n"
+      "define float @test() {\n"
+      "  %A = call nofpclass(zero) float @func()\n"
+      "  ret float %A\n"
+      "}\n");
+  expectKnownFPClass(~fcZero & fcAllFlags, std::nullopt);
+}
+
+TEST_F(ComputeKnownFPClassTest, SelectNoFPClassDeclarationNoNan) {
+  parseAssembly(
+      "declare nofpclass(nan) float @no_nans()\n"
+      "define float @test() {\n"
+      "  %A = call float @no_nans()\n"
+      "  ret float %A\n"
+      "}\n");
+  expectKnownFPClass(~fcNan & fcAllFlags, std::nullopt);
+}
+
+// Check nofpclass + ninf works on a callsite
+TEST_F(ComputeKnownFPClassTest, SelectNoFPClassCallSiteNoZerosNInfFlags) {
+  parseAssembly(
+      "declare float @func()\n"
+      "define float @test() {\n"
+      "  %A = call ninf nofpclass(zero) float @func()\n"
+      "  ret float %A\n"
+      "}\n");
+  expectKnownFPClass(~(fcZero | fcInf) & fcAllFlags, std::nullopt);
+}
+
 TEST_F(ComputeKnownFPClassTest, FNegNInf) {
   parseAssembly(
       "define float @test(float %arg) {\n"