[clang][X86] Update excessive register save diagnostic to more closely follow the interrupt attribute spec

The original diagnostic does not cover all cases according to my reading
of the spec.

For the interrupt attribute, the spec indicates that if the compiler
does not support saving SSE, MMX, or x87 then the function should
be compiled with '-mgeneral-regs-only' (GCC requires this).
Alternatively, calling functions with the `no_caller_saved_registers`
attribute will not clobber state and can be done without disabling
these features.

The warning as implemented in upstream only detects the latter case but
does not consider that disabling the above features also solves the issue
of these register saves being undesirable due to inefficiency.

For the no_caller_saved_registers attribute, the interrupt spec also
indicates that in the absence of saving SSE, MMX and x87 state, these
functions should be compiled with '-mgeneral-regs-only' (also required
by GCC). It does not make any statements about calling other functions
with the attribute, but by extension the result is the same as with the
interrupt attribute (in clang, at least).

This patch handles the remaining cases by adjusting the diagnostic to:

1. Not be shown if the function is compiled without the SSE, MMX or x87
   features enabled (i.e. with '-mgeneral-regs-only')
2. Also be shown for functions with the 'no_caller_saved_registers'
   attribute
3. In addition to advising that the function should only call functions
   with the `no_caller_saved_registers` attribute, the text also suggests
   compiling with `-mgeneral-regs-only` as an alternative.

The interrupt spec is available at https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=5ed3cc7b66af4758f7849ed6f65f4365be8223be
and was taken from the issue that resulted in this diagnostic being
added (llvm#26787)

Reviewed By: pengfei

Differential Revision: https://reviews.llvm.org/D159068

Author: antangelo

clang/docs/ReleaseNotes.rst

@@ -122,12 +122,18 @@ Modified Compiler Flags
 -----------------------
 
 * ``-Woverriding-t-option`` is renamed to ``-Woverriding-option``.
+* ``-Winterrupt-service-routine`` is renamed to ``-Wexcessive-regsave`` as a generalization
 
 Removed Compiler Flags
 -------------------------
 
 Attribute Changes in Clang
 --------------------------
+- On X86, a warning is now emitted if a function with ``__attribute__((no_caller_saved_registers))``
+  calls a function without ``__attribute__((no_caller_saved_registers))``, and is not compiled with
+  ``-mgeneral-regs-only``
+- On X86, a function with ``__attribute__((interrupt))`` can now call a function without
+  ``__attribute__((no_caller_saved_registers))`` provided that it is compiled with ``-mgeneral-regs-only``
 
 - When a non-variadic function is decorated with the ``format`` attribute,
   Clang now checks that the format string would match the function's parameters'

clang/include/clang/Basic/AttrDocs.td

@@ -4815,6 +4815,10 @@ The user can call functions specified with the 'no_caller_saved_registers'
 attribute from an interrupt handler without saving and restoring all
 call-clobbered registers.
 
+Functions specified with the 'no_caller_saved_registers' attribute should only
+call other functions with the 'no_caller_saved_registers' attribute, or should be
+compiled with the '-mgeneral-regs-only' flag to avoid saving unused non-GPR registers.
+
 Note that 'no_caller_saved_registers' attribute is not a calling convention.
 In fact, it only overrides the decision of which registers should be saved by
 the caller, but not how the parameters are passed from the caller to the callee.

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -310,10 +310,12 @@ def err_anyx86_interrupt_attribute : Error<
   "a pointer as the first parameter|a %2 type as the second parameter}1">;
 def err_anyx86_interrupt_called : Error<
   "interrupt service routine cannot be called directly">;
-def warn_anyx86_interrupt_regsave : Warning<
-  "interrupt service routine should only call a function"
-  " with attribute 'no_caller_saved_registers'">,
-  InGroup<DiagGroup<"interrupt-service-routine">>;
+def warn_anyx86_excessive_regsave : Warning<
+  "%select{interrupt service routine|function with attribute"
+  " 'no_caller_saved_registers'}0 should only call a function"
+  " with attribute 'no_caller_saved_registers'"
+  " or be compiled with '-mgeneral-regs-only'">,
+  InGroup<DiagGroup<"excessive-regsave">>;
 def warn_arm_interrupt_calling_convention : Warning<
    "call to function without interrupt attribute could clobber interruptee's VFP registers">,
    InGroup<Extra>;

clang/lib/Sema/SemaExpr.cpp

@@ -7413,11 +7413,18 @@ ExprResult Sema::BuildResolvedCallExpr(Expr *Fn, NamedDecl *NDecl,
           Diag(FDecl->getLocation(), diag::note_callee_decl) << FDecl;
       }
     }
-    if (Caller->hasAttr<AnyX86InterruptAttr>() &&
-        ((!FDecl || !FDecl->hasAttr<AnyX86NoCallerSavedRegistersAttr>()))) {
-      Diag(Fn->getExprLoc(), diag::warn_anyx86_interrupt_regsave);
-      if (FDecl)
-        Diag(FDecl->getLocation(), diag::note_callee_decl) << FDecl;
+    if (Caller->hasAttr<AnyX86InterruptAttr>() ||
+        Caller->hasAttr<AnyX86NoCallerSavedRegistersAttr>()) {
+      const TargetInfo &TI = Context.getTargetInfo();
+      bool HasNonGPRRegisters =
+          TI.hasFeature("sse") || TI.hasFeature("x87") || TI.hasFeature("mmx");
+      if (HasNonGPRRegisters &&
+          (!FDecl || !FDecl->hasAttr<AnyX86NoCallerSavedRegistersAttr>())) {
+        Diag(Fn->getExprLoc(), diag::warn_anyx86_excessive_regsave)
+            << (Caller->hasAttr<AnyX86InterruptAttr>() ? 0 : 1);
+        if (FDecl)
+          Diag(FDecl->getLocation(), diag::note_callee_decl) << FDecl;
+      }
     }
   }
 

clang/test/Sema/attr-x86-interrupt.c

@@ -40,23 +40,6 @@ __attribute__((interrupt)) void foo6(float *a, int b) {}
 __attribute__((interrupt)) void foo7(int *a, unsigned b) {}
 __attribute__((interrupt)) void foo8(int *a) {}
 
-#ifdef _LP64
-typedef unsigned long Arg2Type;
-#elif defined(__x86_64__)
-typedef unsigned long long Arg2Type;
-#else
-typedef unsigned int Arg2Type;
-#endif
-#ifndef NOCALLERSAVE
-__attribute__((no_caller_saved_registers))
-#else
-// expected-note@+3 {{'foo9' declared here}}
-// expected-warning@+4 {{interrupt service routine should only call a function with attribute 'no_caller_saved_registers'}}
-#endif
-void foo9(int *a, Arg2Type b) {}
-__attribute__((interrupt)) void fooA(int *a, Arg2Type b) {
-  foo9(a, b);
-}
 void g(void (*fp)(int *));
 int main(int argc, char **argv) {
   void *ptr = (void *)&foo7;

clang/test/Sema/x86-diag-excessive-regsave.c

@@ -0,0 +1,34 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fsyntax-only -verify %s -DNO_CALLER_SAVED_REGISTERS=1
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -target-feature -x87 -target-feature -mmx -target-feature -sse -fsyntax-only -verify %s -DGPRONLY=1
+
+#if defined(NO_CALLER_SAVED_REGS) || defined(GPRONLY)
+// expected-no-diagnostics
+#else
+#define EXPECT_WARNING
+#endif
+
+#ifdef NO_CALLER_SAVED_REGS
+__attribute__((no_caller_saved_registers))
+#endif
+#ifdef EXPECT_WARNING
+// expected-note@+3 {{'foo' declared here}}
+// expected-note@+2 {{'foo' declared here}}
+#endif
+extern void foo(void *);
+
+__attribute__((no_caller_saved_registers))
+void no_caller_saved_registers(void *arg) {
+#ifdef EXPECT_WARNING
+// expected-warning@+2 {{function with attribute 'no_caller_saved_registers' should only call a function with attribute 'no_caller_saved_registers' or be compiled with '-mgeneral-regs-only'}}
+#endif
+    foo(arg);
+}
+
+__attribute__((interrupt))
+void interrupt(void *arg) {
+#ifdef EXPECT_WARNING
+// expected-warning@+2 {{interrupt service routine should only call a function with attribute 'no_caller_saved_registers' or be compiled with '-mgeneral-regs-only'}}
+#endif
+    foo(arg);
+}