Separate "ZT0 undef" from StateValue

This allows this to be independent from new/preserves/shares ZT0.

Author: MacDue

llvm/lib/Target/AArch64/Utils/AArch64SMEAttributes.cpp

@@ -75,6 +75,8 @@ SMEAttrs::SMEAttrs(const AttributeList &Attrs) {
     Bitmask |= SM_Body;
   if (Attrs.hasFnAttr("aarch64_za_state_agnostic"))
     Bitmask |= ZA_State_Agnostic;
+  if (Attrs.hasFnAttr("aarch64_zt0_undef"))
+    Bitmask |= ZT0_Undef;
   if (Attrs.hasFnAttr("aarch64_in_za"))
     Bitmask |= encodeZAState(StateValue::In);
   if (Attrs.hasFnAttr("aarch64_out_za"))
@@ -95,8 +97,6 @@ SMEAttrs::SMEAttrs(const AttributeList &Attrs) {
     Bitmask |= encodeZT0State(StateValue::Preserved);
   if (Attrs.hasFnAttr("aarch64_new_zt0"))
     Bitmask |= encodeZT0State(StateValue::New);
-  if (Attrs.hasFnAttr("aarch64_zt0_undef"))
-    Bitmask |= encodeZT0State(StateValue::Undef);
 }
 
 bool SMEAttrs::requiresSMChange(const SMEAttrs &Callee) const {

llvm/lib/Target/AArch64/Utils/AArch64SMEAttributes.h

@@ -32,8 +32,7 @@ class SMEAttrs {
     Out = 2,       // aarch64_out_zt0
     InOut = 3,     // aarch64_inout_zt0
     Preserved = 4, // aarch64_preserves_zt0
-    New = 5,       // aarch64_new_zt0
-    Undef = 6      // aarch64_zt0_undef
+    New = 5        // aarch64_new_zt0
   };
 
   // Enum with bitmasks for each individual SME feature.
@@ -44,9 +43,10 @@ class SMEAttrs {
     SM_Body = 1 << 2,         // aarch64_pstate_sm_body
     SME_ABI_Routine = 1 << 3, // Used for SME ABI routines to avoid lazy saves
     ZA_State_Agnostic = 1 << 4,
-    ZA_Shift = 5,
+    ZT0_Undef = 1 << 5,       // Use to mark ZT0 as undef to avoid spills
+    ZA_Shift = 6,
     ZA_Mask = 0b111 << ZA_Shift,
-    ZT0_Shift = 8,
+    ZT0_Shift = 9,
     ZT0_Mask = 0b111 << ZT0_Shift
   };
 
@@ -126,9 +126,7 @@ class SMEAttrs {
   bool isPreservesZT0() const {
     return decodeZT0State(Bitmask) == StateValue::Preserved;
   }
-  bool isUndefZT0() const {
-    return decodeZT0State(Bitmask) == StateValue::Undef;
-  }
+  bool isUndefZT0() const { return Bitmask & ZT0_Undef; }
   bool sharesZT0() const {
     StateValue State = decodeZT0State(Bitmask);
     return State == StateValue::In || State == StateValue::Out ||

llvm/unittests/Target/AArch64/SMEAttributesTest.cpp

@@ -225,14 +225,14 @@ TEST(SMEAttributes, Basics) {
   ASSERT_FALSE(ZT0_New.hasSharedZAInterface());
   ASSERT_TRUE(ZT0_New.hasPrivateZAInterface());
 
-  SA ZT0_Undef = SA(SA::encodeZT0State(SA::StateValue::Undef));
-  ASSERT_FALSE(ZT0_Undef.isNewZT0());
+  SA ZT0_Undef = SA(SA::ZT0_Undef | SA::encodeZT0State(SA::StateValue::New));
+  ASSERT_TRUE(ZT0_Undef.isNewZT0());
   ASSERT_FALSE(ZT0_Undef.isInZT0());
   ASSERT_FALSE(ZT0_Undef.isOutZT0());
   ASSERT_FALSE(ZT0_Undef.isInOutZT0());
   ASSERT_FALSE(ZT0_Undef.isPreservesZT0());
   ASSERT_FALSE(ZT0_Undef.sharesZT0());
-  ASSERT_FALSE(ZT0_Undef.hasZT0State());
+  ASSERT_TRUE(ZT0_Undef.hasZT0State());
   ASSERT_FALSE(ZT0_Undef.hasSharedZAInterface());
   ASSERT_TRUE(ZT0_Undef.hasPrivateZAInterface());
   ASSERT_TRUE(ZT0_Undef.isUndefZT0());
@@ -307,7 +307,7 @@ TEST(SMEAttributes, Transitions) {
   SA ZT0_Shared = SA(SA::encodeZT0State(SA::StateValue::In));
   SA ZA_ZT0_Shared = SA(SA::encodeZAState(SA::StateValue::In) |
                         SA::encodeZT0State(SA::StateValue::In));
-  SA Undef_ZT0 = SA((SA::encodeZT0State(SA::StateValue::Undef)));
+  SA Undef_ZT0 = SA(SA::ZT0_Undef);
 
   // Shared ZA -> Private ZA Interface
   ASSERT_FALSE(ZA_Shared.requiresDisablingZABeforeCall(Private_ZA));