[llvm] [KnownFPClass] Add output/input denormal helpers (PR #225575)

[Eric Ross via llvm-commits]

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@@ -23,48 +23,70 @@ KnownFPClass::KnownFPClass(const APFloat &C)
   setSignBit(C.isNegative());
 }
 
-/// Return true if it's possible to assume IEEE treatment of input denormals in
-/// \p F for \p Val.
-static bool inputDenormalIsIEEE(DenormalMode Mode) {
-  return Mode.Input == DenormalMode::IEEE;
+KnownFPClass KnownFPClass::applyInputDenormalMode(const KnownFPClass &KnownSrc,
+                                                  DenormalMode Mode) {
+  KnownFPClass Known = KnownSrc;
+  switch (Mode.Input) {
+  case DenormalMode::IEEE:
+    return Known;
+  case DenormalMode::PreserveSign:
+    if (KnownSrc.getKnownFPClasses() & fcPosSubnormal)
+      Known.setKnownFPClasses(Known.getKnownFPClasses() | fcPosZero);
+    if (KnownSrc.getKnownFPClasses() & fcNegSubnormal)
+      Known.setKnownFPClasses(Known.getKnownFPClasses() | fcNegZero);
+    return Known;
+  case DenormalMode::PositiveZero:
+    if (KnownSrc.getKnownFPClasses() & fcSubnormal)
+      Known.setKnownFPClasses(Known.getKnownFPClasses() | fcPosZero);
+    return Known;
+  default:
+    if (KnownSrc.getKnownFPClasses() & fcSubnormal)
+      Known.setKnownFPClasses(Known.getKnownFPClasses() | fcPosZero);
+    if (KnownSrc.getKnownFPClasses() & fcNegSubnormal)
+      Known.setKnownFPClasses(Known.getKnownFPClasses() | fcNegZero);
+    return Known;
+  }
+
+  llvm_unreachable("covered switch over denormal mode");
 }
 
-static bool inputDenormalIsIEEEOrPosZero(DenormalMode Mode) {
-  return Mode.Input == DenormalMode::IEEE ||
-         Mode.Input == DenormalMode::PositiveZero;
+KnownFPClass KnownFPClass::applyOutputDenormalMode(const KnownFPClass &KnownSrc,
+                                                   DenormalMode Mode) {
+  KnownFPClass Known = KnownSrc;
+  switch (Mode.Output) {
+  case DenormalMode::IEEE:
+    return Known;
+  case DenormalMode::PreserveSign:
+    if (KnownSrc.getKnownFPClasses() & fcPosSubnormal)
+      Known.setKnownFPClasses(Known.getKnownFPClasses() | fcPosZero);
+    if (KnownSrc.getKnownFPClasses() & fcNegSubnormal)
+      Known.setKnownFPClasses(Known.getKnownFPClasses() | fcNegZero);
+    return Known;
+  case DenormalMode::PositiveZero:
+    if (KnownSrc.getKnownFPClasses() & fcSubnormal)
+      Known.setKnownFPClasses(Known.getKnownFPClasses() | fcPosZero);
+    return Known;
+  default:
+    if (KnownSrc.getKnownFPClasses() & fcSubnormal)
+      Known.setKnownFPClasses(Known.getKnownFPClasses() | fcPosZero);
+    if (KnownSrc.getKnownFPClasses() & fcNegSubnormal)
+      Known.setKnownFPClasses(Known.getKnownFPClasses() | fcNegZero);
+    return Known;
+  }
+
+  llvm_unreachable("covered switch over denormal mode");
 }
 
 bool KnownFPClass::isKnownNeverLogicalZero(DenormalMode Mode) const {
-  return isKnownNeverZero() &&
-         (isKnownNeverSubnormal() || inputDenormalIsIEEE(Mode));
+  return applyInputDenormalMode(*this, Mode).isKnownNeverZero();
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ZERICO2005 wrote:

The benefit of doing it this way (other than for testing purposes) is that everything automatically follows how `applyInputDenormalMode` handles the `DenormalMode`.

https://github.com/llvm/llvm-project/pull/225575