[llvm] 8c7a2ce - [AArch64][SME] Allow spills of ZT0 around SME ABI routines again (#136726)
via llvm-commits
llvm-commits at lists.llvm.org
Fri Apr 25 05:33:13 PDT 2025
Author: Benjamin Maxwell
Date: 2025-04-25T13:33:09+01:00
New Revision: 8c7a2ce01a77c96028fe2c8566f65c45ad9408d3
URL: https://github.com/llvm/llvm-project/commit/8c7a2ce01a77c96028fe2c8566f65c45ad9408d3
DIFF: https://github.com/llvm/llvm-project/commit/8c7a2ce01a77c96028fe2c8566f65c45ad9408d3.diff
LOG: [AArch64][SME] Allow spills of ZT0 around SME ABI routines again (#136726)
In #132722 spills of ZT0 were disabled around all SME ABI routines to
avoid a case where ZT0 is spilled before ZA is enabled (resulting in a
crash).
It turns out that the ABI does not promise that routines will preserve
ZT0 (however in practice they do), so generally disabling ZT0 spills for
ABI routines is not correct.
The case where a crash was possible was "aarch64_new_zt0" functions with
ZA disabled on entry and a ZT0 spill around __arm_tpidr2_save. In this
case, ZT0 will be undefined at the call to __arm_tpidr2_save, so this
patch avoids the ZT0 spill by marking the callsite with
"aarch64_zt0_undef". This attribute only applies to callsites and marks
that at the point the call is made ZT0 is not defined, so does not need
preserving.
Added:
llvm/test/CodeGen/AArch64/sme-new-zt0-function.ll
Modified:
llvm/lib/IR/Verifier.cpp
llvm/lib/Target/AArch64/SMEABIPass.cpp
llvm/lib/Target/AArch64/Utils/AArch64SMEAttributes.cpp
llvm/lib/Target/AArch64/Utils/AArch64SMEAttributes.h
llvm/test/CodeGen/AArch64/sme-zt0-state.ll
llvm/test/Verifier/sme-attributes.ll
llvm/unittests/Target/AArch64/SMEAttributesTest.cpp
Removed:
################################################################################
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 843a78c1f41ad..84054ddd0298c 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -2859,6 +2859,9 @@ void Verifier::visitFunction(const Function &F) {
Check(!Attrs.hasAttrSomewhere(Attribute::ElementType),
"Attribute 'elementtype' can only be applied to a callsite.", &F);
+ Check(!Attrs.hasFnAttr("aarch64_zt0_undef"),
+ "Attribute 'aarch64_zt0_undef' can only be applied to a callsite.");
+
if (Attrs.hasFnAttr(Attribute::Naked))
for (const Argument &Arg : F.args())
Check(Arg.use_empty(), "cannot use argument of naked function", &Arg);
diff --git a/llvm/lib/Target/AArch64/SMEABIPass.cpp b/llvm/lib/Target/AArch64/SMEABIPass.cpp
index bb885d86392fe..b6685497e1fd1 100644
--- a/llvm/lib/Target/AArch64/SMEABIPass.cpp
+++ b/llvm/lib/Target/AArch64/SMEABIPass.cpp
@@ -54,14 +54,22 @@ FunctionPass *llvm::createSMEABIPass() { return new SMEABI(); }
//===----------------------------------------------------------------------===//
// Utility function to emit a call to __arm_tpidr2_save and clear TPIDR2_EL0.
-void emitTPIDR2Save(Module *M, IRBuilder<> &Builder) {
+void emitTPIDR2Save(Module *M, IRBuilder<> &Builder, bool ZT0IsUndef = false) {
+ auto &Ctx = M->getContext();
auto *TPIDR2SaveTy =
FunctionType::get(Builder.getVoidTy(), {}, /*IsVarArgs=*/false);
- auto Attrs = AttributeList().addFnAttribute(M->getContext(),
- "aarch64_pstate_sm_compatible");
+ auto Attrs =
+ AttributeList().addFnAttribute(Ctx, "aarch64_pstate_sm_compatible");
FunctionCallee Callee =
M->getOrInsertFunction("__arm_tpidr2_save", TPIDR2SaveTy, Attrs);
CallInst *Call = Builder.CreateCall(Callee);
+
+ // If ZT0 is undefined (i.e. we're at the entry of a "new_zt0" function), mark
+ // that on the __arm_tpidr2_save call. This prevents an unnecessary spill of
+ // ZT0 that can occur before ZA is enabled.
+ if (ZT0IsUndef)
+ Call->addFnAttr(Attribute::get(Ctx, "aarch64_zt0_undef"));
+
Call->setCallingConv(
CallingConv::AArch64_SME_ABI_Support_Routines_PreserveMost_From_X0);
@@ -119,7 +127,7 @@ bool SMEABI::updateNewStateFunctions(Module *M, Function *F,
// Create a call __arm_tpidr2_save, which commits the lazy save.
Builder.SetInsertPoint(&SaveBB->back());
- emitTPIDR2Save(M, Builder);
+ emitTPIDR2Save(M, Builder, /*ZT0IsUndef=*/FnAttrs.isNewZT0());
// Enable pstate.za at the start of the function.
Builder.SetInsertPoint(&OrigBB->front());
diff --git a/llvm/lib/Target/AArch64/Utils/AArch64SMEAttributes.cpp b/llvm/lib/Target/AArch64/Utils/AArch64SMEAttributes.cpp
index bf16acd7f8f7e..76d2ac6a601e5 100644
--- a/llvm/lib/Target/AArch64/Utils/AArch64SMEAttributes.cpp
+++ b/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"))
diff --git a/llvm/lib/Target/AArch64/Utils/AArch64SMEAttributes.h b/llvm/lib/Target/AArch64/Utils/AArch64SMEAttributes.h
index a3ebf764a6e0c..1691d4fec8b68 100644
--- a/llvm/lib/Target/AArch64/Utils/AArch64SMEAttributes.h
+++ b/llvm/lib/Target/AArch64/Utils/AArch64SMEAttributes.h
@@ -43,9 +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
};
@@ -125,6 +126,7 @@ class SMEAttrs {
bool isPreservesZT0() const {
return decodeZT0State(Bitmask) == StateValue::Preserved;
}
+ bool isUndefZT0() const { return Bitmask & ZT0_Undef; }
bool sharesZT0() const {
StateValue State = decodeZT0State(Bitmask);
return State == StateValue::In || State == StateValue::Out ||
@@ -132,9 +134,8 @@ class SMEAttrs {
}
bool hasZT0State() const { return isNewZT0() || sharesZT0(); }
bool requiresPreservingZT0(const SMEAttrs &Callee) const {
- return hasZT0State() && !Callee.sharesZT0() &&
- !Callee.hasAgnosticZAInterface() &&
- !(Callee.Bitmask & SME_ABI_Routine);
+ return hasZT0State() && !Callee.isUndefZT0() && !Callee.sharesZT0() &&
+ !Callee.hasAgnosticZAInterface();
}
bool requiresDisablingZABeforeCall(const SMEAttrs &Callee) const {
return hasZT0State() && !hasZAState() && Callee.hasPrivateZAInterface() &&
diff --git a/llvm/test/CodeGen/AArch64/sme-new-zt0-function.ll b/llvm/test/CodeGen/AArch64/sme-new-zt0-function.ll
new file mode 100644
index 0000000000000..94968ab4fd9ac
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/sme-new-zt0-function.ll
@@ -0,0 +1,14 @@
+; RUN: opt -S -mtriple=aarch64-linux-gnu -aarch64-sme-abi %s | FileCheck %s
+
+declare void @callee();
+
+define void @private_za() "aarch64_new_zt0" {
+ call void @callee()
+ ret void
+}
+
+; CHECK: call aarch64_sme_preservemost_from_x0 void @__arm_tpidr2_save() #[[TPIDR2_SAVE_CALL_ATTR:[0-9]+]]
+; CHECK: declare void @__arm_tpidr2_save() #[[TPIDR2_SAVE_DECL_ATTR:[0-9]+]]
+
+; CHECK: attributes #[[TPIDR2_SAVE_DECL_ATTR]] = { "aarch64_pstate_sm_compatible" }
+; CHECK: attributes #[[TPIDR2_SAVE_CALL_ATTR]] = { "aarch64_zt0_undef" }
diff --git a/llvm/test/CodeGen/AArch64/sme-zt0-state.ll b/llvm/test/CodeGen/AArch64/sme-zt0-state.ll
index 500fff4eb20db..7361e850d713e 100644
--- a/llvm/test/CodeGen/AArch64/sme-zt0-state.ll
+++ b/llvm/test/CodeGen/AArch64/sme-zt0-state.ll
@@ -167,6 +167,39 @@ define void @zt0_new_caller_zt0_new_callee() "aarch64_new_zt0" nounwind {
ret void;
}
+; Expect commit of lazy-save if ZA is dormant
+; Expect smstart ZA & clear ZT0
+; No spill & fill of ZT0 around __arm_tpidr2_save
+; Expect spill & fill of ZT0 around __arm_sme_state call
+; Before return, expect smstop ZA
+define i64 @zt0_new_caller_abi_routine_callee() "aarch64_new_zt0" nounwind {
+; CHECK-LABEL: zt0_new_caller_abi_routine_callee:
+; CHECK: // %bb.0: // %prelude
+; CHECK-NEXT: sub sp, sp, #80
+; CHECK-NEXT: stp x30, x19, [sp, #64] // 16-byte Folded Spill
+; CHECK-NEXT: mrs x8, TPIDR2_EL0
+; CHECK-NEXT: cbz x8, .LBB7_2
+; CHECK-NEXT: // %bb.1: // %save.za
+; CHECK-NEXT: bl __arm_tpidr2_save
+; CHECK-NEXT: msr TPIDR2_EL0, xzr
+; CHECK-NEXT: .LBB7_2:
+; CHECK-NEXT: smstart za
+; CHECK-NEXT: zero { zt0 }
+; CHECK-NEXT: mov x19, sp
+; CHECK-NEXT: str zt0, [x19]
+; CHECK-NEXT: bl __arm_sme_state
+; CHECK-NEXT: ldr zt0, [x19]
+; CHECK-NEXT: smstop za
+; CHECK-NEXT: ldp x30, x19, [sp, #64] // 16-byte Folded Reload
+; CHECK-NEXT: add sp, sp, #80
+; CHECK-NEXT: ret
+ %res = call {i64, i64} @__arm_sme_state()
+ %res.0 = extractvalue {i64, i64} %res, 0
+ ret i64 %res.0
+}
+
+declare {i64, i64} @__arm_sme_state()
+
;
; New-ZA Caller
;
@@ -179,11 +212,11 @@ define void @zt0_new_caller() "aarch64_new_zt0" nounwind {
; CHECK: // %bb.0: // %prelude
; CHECK-NEXT: str x30, [sp, #-16]! // 8-byte Folded Spill
; CHECK-NEXT: mrs x8, TPIDR2_EL0
-; CHECK-NEXT: cbz x8, .LBB7_2
+; CHECK-NEXT: cbz x8, .LBB8_2
; CHECK-NEXT: // %bb.1: // %save.za
; CHECK-NEXT: bl __arm_tpidr2_save
; CHECK-NEXT: msr TPIDR2_EL0, xzr
-; CHECK-NEXT: .LBB7_2:
+; CHECK-NEXT: .LBB8_2:
; CHECK-NEXT: smstart za
; CHECK-NEXT: zero { zt0 }
; CHECK-NEXT: bl callee
@@ -202,11 +235,11 @@ define void @new_za_zt0_caller() "aarch64_new_za" "aarch64_new_zt0" nounwind {
; CHECK: // %bb.0: // %prelude
; CHECK-NEXT: str x30, [sp, #-16]! // 8-byte Folded Spill
; CHECK-NEXT: mrs x8, TPIDR2_EL0
-; CHECK-NEXT: cbz x8, .LBB8_2
+; CHECK-NEXT: cbz x8, .LBB9_2
; CHECK-NEXT: // %bb.1: // %save.za
; CHECK-NEXT: bl __arm_tpidr2_save
; CHECK-NEXT: msr TPIDR2_EL0, xzr
-; CHECK-NEXT: .LBB8_2:
+; CHECK-NEXT: .LBB9_2:
; CHECK-NEXT: smstart za
; CHECK-NEXT: zero {za}
; CHECK-NEXT: zero { zt0 }
diff --git a/llvm/test/Verifier/sme-attributes.ll b/llvm/test/Verifier/sme-attributes.ll
index 4bf5e813daf2f..0ae2b9fd91f52 100644
--- a/llvm/test/Verifier/sme-attributes.ll
+++ b/llvm/test/Verifier/sme-attributes.ll
@@ -68,3 +68,6 @@ declare void @zt0_inout_out() "aarch64_inout_zt0" "aarch64_out_zt0";
declare void @zt0_inout_agnostic() "aarch64_inout_zt0" "aarch64_za_state_agnostic";
; CHECK: Attributes 'aarch64_new_zt0', 'aarch64_in_zt0', 'aarch64_out_zt0', 'aarch64_inout_zt0', 'aarch64_preserves_zt0' and 'aarch64_za_state_agnostic' are mutually exclusive
+
+declare void @zt0_undef_function() "aarch64_zt0_undef";
+; CHECK: Attribute 'aarch64_zt0_undef' can only be applied to a callsite.
diff --git a/llvm/unittests/Target/AArch64/SMEAttributesTest.cpp b/llvm/unittests/Target/AArch64/SMEAttributesTest.cpp
index 3af5e24168c8c..f8c77fcba19cf 100644
--- a/llvm/unittests/Target/AArch64/SMEAttributesTest.cpp
+++ b/llvm/unittests/Target/AArch64/SMEAttributesTest.cpp
@@ -1,6 +1,7 @@
#include "Utils/AArch64SMEAttributes.h"
#include "llvm/AsmParser/Parser.h"
#include "llvm/IR/Function.h"
+#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/SourceMgr.h"
@@ -69,6 +70,15 @@ TEST(SMEAttributes, Constructors) {
ASSERT_TRUE(SA(*parseIR("declare void @foo() \"aarch64_new_zt0\"")
->getFunction("foo"))
.isNewZT0());
+ ASSERT_TRUE(
+ SA(cast<CallBase>((parseIR("declare void @callee()\n"
+ "define void @foo() {"
+ "call void @callee() \"aarch64_zt0_undef\"\n"
+ "ret void\n}")
+ ->getFunction("foo")
+ ->begin()
+ ->front())))
+ .isUndefZT0());
// Invalid combinations.
EXPECT_DEBUG_DEATH(SA(SA::SM_Enabled | SA::SM_Compatible),
@@ -215,6 +225,18 @@ TEST(SMEAttributes, Basics) {
ASSERT_FALSE(ZT0_New.hasSharedZAInterface());
ASSERT_TRUE(ZT0_New.hasPrivateZAInterface());
+ 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_TRUE(ZT0_Undef.hasZT0State());
+ ASSERT_FALSE(ZT0_Undef.hasSharedZAInterface());
+ ASSERT_TRUE(ZT0_Undef.hasPrivateZAInterface());
+ ASSERT_TRUE(ZT0_Undef.isUndefZT0());
+
ASSERT_FALSE(SA(SA::Normal).isInZT0());
ASSERT_FALSE(SA(SA::Normal).isOutZT0());
ASSERT_FALSE(SA(SA::Normal).isInOutZT0());
@@ -285,6 +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::ZT0_Undef);
// Shared ZA -> Private ZA Interface
ASSERT_FALSE(ZA_Shared.requiresDisablingZABeforeCall(Private_ZA));
@@ -295,6 +318,13 @@ TEST(SMEAttributes, Transitions) {
ASSERT_TRUE(ZT0_Shared.requiresPreservingZT0(Private_ZA));
ASSERT_TRUE(ZT0_Shared.requiresEnablingZAAfterCall(Private_ZA));
+ // Shared Undef ZT0 -> Private ZA Interface
+ // Note: "Undef ZT0" is a callsite attribute that means ZT0 is undefined at
+ // point the of the call.
+ ASSERT_TRUE(ZT0_Shared.requiresDisablingZABeforeCall(Undef_ZT0));
+ ASSERT_FALSE(ZT0_Shared.requiresPreservingZT0(Undef_ZT0));
+ ASSERT_TRUE(ZT0_Shared.requiresEnablingZAAfterCall(Undef_ZT0));
+
// Shared ZA & ZT0 -> Private ZA Interface
ASSERT_FALSE(ZA_ZT0_Shared.requiresDisablingZABeforeCall(Private_ZA));
ASSERT_TRUE(ZA_ZT0_Shared.requiresPreservingZT0(Private_ZA));
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