ValueTracking: Handle ConstantAggregateZero in computeKnownFPClass

Author: arsenm

llvm/lib/Analysis/ValueTracking.cpp

@@ -4507,6 +4507,12 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
     return;
   }
 
+  if (isa<ConstantAggregateZero>(V)) {
+    Known.KnownFPClasses = fcPosZero;
+    Known.SignBit = false;
+    return;
+  }
+
   // Try to handle fixed width vector constants
   auto *VFVTy = dyn_cast<FixedVectorType>(V->getType());
   const Constant *CV = dyn_cast<Constant>(V);

llvm/test/Transforms/Attributor/nofpclass.ll

@@ -2644,7 +2644,7 @@ bb:
 
 define [4 x float] @constant_aggregate_zero() {
 ; CHECK: Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none)
-; CHECK-LABEL: define [4 x float] @constant_aggregate_zero
+; CHECK-LABEL: define nofpclass(nan inf nzero sub norm) [4 x float] @constant_aggregate_zero
 ; CHECK-SAME: () #[[ATTR3]] {
 ; CHECK-NEXT:    ret [4 x float] zeroinitializer
 ;
@@ -2662,7 +2662,7 @@ define <vscale x 4 x float> @scalable_splat_pnorm() {
 
 define <vscale x 4 x float> @scalable_splat_zero() {
 ; CHECK: Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none)
-; CHECK-LABEL: define noundef <vscale x 4 x float> @scalable_splat_zero
+; CHECK-LABEL: define noundef nofpclass(nan inf nzero sub norm) <vscale x 4 x float> @scalable_splat_zero
 ; CHECK-SAME: () #[[ATTR3]] {
 ; CHECK-NEXT:    ret <vscale x 4 x float> zeroinitializer
 ;

llvm/unittests/Analysis/ValueTrackingTest.cpp

@@ -2016,6 +2016,27 @@ TEST_F(ComputeKnownFPClassTest, SqrtNszSignBit) {
   }
 }
 
+TEST_F(ComputeKnownFPClassTest, Constants) {
+  parseAssembly("declare float @func()\n"
+                "define float @test() {\n"
+                "  %A = call float @func()\n"
+                "  ret float %A\n"
+                "}\n");
+
+  Type *F32 = Type::getFloatTy(Context);
+  Type *V4F32 = FixedVectorType::get(F32, 4);
+
+  {
+    KnownFPClass ConstAggZero = computeKnownFPClass(
+        ConstantAggregateZero::get(V4F32), M->getDataLayout(), fcAllFlags, 0,
+        nullptr, nullptr, nullptr, nullptr);
+
+    EXPECT_EQ(fcPosZero, ConstAggZero.KnownFPClasses);
+    ASSERT_TRUE(ConstAggZero.SignBit);
+    EXPECT_FALSE(*ConstAggZero.SignBit);
+  }
+}
+
 TEST_F(ValueTrackingTest, isNonZeroRecurrence) {
   parseAssembly(R"(
     define i1 @test(i8 %n, i8 %r) {