[llvm] [AArch64] Restore always-inline behaviour for incompatible SME attributes. (PR #218727)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Sander de Smalen (sdesmalen-arm)

<details>
<summary>Changes</summary>

PR #<!-- -->209345 changed inlining behaviour for 'alwaysinline' functions
when the callee's SME attributes were incompatible with the caller's
SME attributes. This is not desirable, as it would stop small utility
routines being inlined into streaming functions (such as std::max).

This PR restores the original behaviour from before #<!-- -->209345.

Fixes https://github.com/llvm/llvm-project/issues/217639

---
Full diff: https://github.com/llvm/llvm-project/pull/218727.diff


2 Files Affected:

- (modified) llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp (+6-1) 
- (added) llvm/test/Transforms/Inline/AArch64/sme-always-inline.ll (+23) 


``````````diff
diff --git a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
index 46d2ecfde484e..54a433fdf8f05 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -301,7 +301,12 @@ bool AArch64TTIImpl::areInlineCompatible(const Function *Caller,
   if (CallAttrs.requiresLazySave() || CallAttrs.requiresSMChange() ||
       CallAttrs.requiresPreservingZT0() ||
       CallAttrs.requiresPreservingAllZAState()) {
-    if (hasPossibleIncompatibleOps(Callee, *getTLI()))
+    // For always-inline functions we can ignore the SME attributes as we should
+    // be able to assume that the user knows what they're doing and that the
+    // front-end has given sufficient warning or error diagnostics to guard the
+    // user.
+    if (!Callee->hasFnAttribute(Attribute::AlwaysInline) &&
+        hasPossibleIncompatibleOps(Callee, *getTLI()))
       return false;
   }
 
diff --git a/llvm/test/Transforms/Inline/AArch64/sme-always-inline.ll b/llvm/test/Transforms/Inline/AArch64/sme-always-inline.ll
new file mode 100644
index 0000000000000..4ab23f97e8b5b
--- /dev/null
+++ b/llvm/test/Transforms/Inline/AArch64/sme-always-inline.ll
@@ -0,0 +1,23 @@
+; REQUIRES: aarch64-registered-target
+; RUN: opt -passes=always-inline -S < %s | FileCheck %s
+
+target triple = "aarch64"
+
+define internal float @callee(float %v) #0 {
+; CHECK-NOT: define internal float @callee
+  %res = tail call float @llvm.sin.f32(float %v)
+  ret float %res
+}
+
+define float @caller(float %v) #1 {
+; CHECK-LABEL: define float @caller(
+; CHECK-SAME: float [[V:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    [[RES:%.*]] = call float @llvm.sin.f32(float [[V]])
+; CHECK-NEXT:    ret float [[RES]]
+;
+  %res = call float @callee(float %v)
+  ret float %res
+}
+
+attributes #0 = { "target-features"="+sme2" nounwind alwaysinline }
+attributes #1 = { "target-features"="+sme2" nounwind "aarch64_pstate_sm_enabled" }

``````````

</details>


https://github.com/llvm/llvm-project/pull/218727