Reland: "[Clang] Demote always_inline error to warning for mismatching SME attrs" (#100991) (#100996)

Test `aarch64-sme-inline-streaming-attrs.c` caused some buildbot
failures, because the test was missing a `REQUIRES: aarch64-registered
target`. This was because we've demoted the error to a warning, which
then resulted in a different error message, because Clang can't actually
CodeGen the IR.

Author: sdesmalen-arm

clang/include/clang/Basic/DiagnosticFrontendKinds.td

@@ -288,6 +288,9 @@ def err_function_needs_feature : Error<
 let CategoryName = "Codegen ABI Check" in {
 def err_function_always_inline_attribute_mismatch : Error<
   "always_inline function %1 and its caller %0 have mismatching %2 attributes">;
+def warn_function_always_inline_attribute_mismatch : Warning<
+  "always_inline function %1 and its caller %0 have mismatching %2 attributes, "
+  "inlining may change runtime behaviour">, InGroup<AArch64SMEAttributes>;
 def err_function_always_inline_new_za : Error<
   "always_inline function %0 has new za state">;
 

clang/lib/CodeGen/Targets/AArch64.cpp

@@ -883,8 +883,10 @@ void AArch64TargetCodeGenInfo::checkFunctionCallABIStreaming(
 
   if (!CalleeIsStreamingCompatible &&
       (CallerIsStreaming != CalleeIsStreaming || CallerIsStreamingCompatible))
-    CGM.getDiags().Report(CallLoc,
-                          diag::err_function_always_inline_attribute_mismatch)
+    CGM.getDiags().Report(
+        CallLoc, CalleeIsStreaming
+                     ? diag::err_function_always_inline_attribute_mismatch
+                     : diag::warn_function_always_inline_attribute_mismatch)
         << Caller->getDeclName() << Callee->getDeclName() << "streaming";
   if (auto *NewAttr = Callee->getAttr<ArmNewAttr>())
     if (NewAttr->isNewZA())

clang/test/CodeGen/aarch64-sme-inline-streaming-attrs.c

@@ -3,6 +3,8 @@
 // RUN: %clang_cc1 -triple aarch64-none-linux-gnu -S -o /dev/null -target-feature +sme -verify -DTEST_STREAMING %s
 // RUN: %clang_cc1 -triple aarch64-none-linux-gnu -S -o /dev/null -target-feature +sme -verify -DTEST_LOCALLY %s
 
+// REQUIRES: aarch64-registered-target
+
 #define __ai __attribute__((always_inline))
 __ai void inlined_fn(void) {}
 __ai void inlined_fn_streaming_compatible(void) __arm_streaming_compatible {}
@@ -20,7 +22,7 @@ void caller(void) {
 
 #ifdef TEST_COMPATIBLE
 void caller_compatible(void) __arm_streaming_compatible {
-    inlined_fn(); // expected-error {{always_inline function 'inlined_fn' and its caller 'caller_compatible' have mismatching streaming attributes}}
+    inlined_fn(); // expected-warning {{always_inline function 'inlined_fn' and its caller 'caller_compatible' have mismatching streaming attributes, inlining may change runtime behaviour}}
     inlined_fn_streaming_compatible();
     inlined_fn_streaming(); // expected-error {{always_inline function 'inlined_fn_streaming' and its caller 'caller_compatible' have mismatching streaming attributes}}
     inlined_fn_local(); // expected-error {{always_inline function 'inlined_fn_local' and its caller 'caller_compatible' have mismatching streaming attributes}}
@@ -29,7 +31,7 @@ void caller_compatible(void) __arm_streaming_compatible {
 
 #ifdef TEST_STREAMING
 void caller_streaming(void) __arm_streaming {
-    inlined_fn(); // expected-error {{always_inline function 'inlined_fn' and its caller 'caller_streaming' have mismatching streaming attributes}}
+    inlined_fn(); // expected-warning {{always_inline function 'inlined_fn' and its caller 'caller_streaming' have mismatching streaming attributes, inlining may change runtime behaviour}}
     inlined_fn_streaming_compatible();
     inlined_fn_streaming();
     inlined_fn_local();
@@ -39,7 +41,7 @@ void caller_streaming(void) __arm_streaming {
 #ifdef TEST_LOCALLY
 __arm_locally_streaming
 void caller_local(void) {
-    inlined_fn(); // expected-error {{always_inline function 'inlined_fn' and its caller 'caller_local' have mismatching streaming attributes}}
+    inlined_fn(); // expected-warning {{always_inline function 'inlined_fn' and its caller 'caller_local' have mismatching streaming attributes, inlining may change runtime behaviour}}
     inlined_fn_streaming_compatible();
     inlined_fn_streaming();
     inlined_fn_local();