[FPEnv] Diagnose pragmas FENV_ROUND,_ACCESS and float_control if target does not support StrictFP

[mibintc]

Summary

If the target doesn't support setting StrictFP, then ignore pragmas that modify the settings for rounding mode and exception behavior and FENV_ACCESS.
This was requested by @kpn see https://bugs.llvm.org/show_bug.cgi?id=47536
Also @pengfei suggested it as a solution for https://bugs.llvm.org/show_bug.cgi?id=47990

[kpn]

I also added "-fexperimental-strict-floating-point" which makes it possible to write tests for a target when bringing up the support on that target. I think it would be confusing for that flag to work on command line arguments but not pragmas.

[mibintc]

Modified according to @kpn suggestion: if the command line has option fexperimental-strict-floating-point, the float pragmas will not be ignored.

[mibintc]

In D90316#2359366, @kpn wrote:

I also added "-fexperimental-strict-floating-point" which makes it possible to write tests for a target when bringing up the support on that target. I think it would be confusing for that flag to work on command line arguments but not pragmas.

Thanks, I added this

[aaron.ballman]

clang/lib/Parse/ParsePragma.cpp

107

Can you fix the lint issues (run the patch through clang-format)? Same for below.

2967

Can you pass in PragmaName directly, or does that do unfortunate things with single quotes?

clang/test/Parser/pragma-fp-warn.c

12–14

I'd appreciate reversing the order of the comments so that they're in the same order as the pragmas below.

[mibintc]

respond to @aaron.ballman 's review

[mibintc]

clang/lib/Parse/ParsePragma.cpp

2967

After I changed it to PragmaName, the clang-format didn't find anything to fix

[sepavloff]

LGTM.

clang/test/Parser/pragma-fp-warn.c

2

I would propose to add a line with -triple msp430. This is a simple core, it is unlikely that it gets hardware FP support.

clang/include/clang/Basic/DiagnosticParseKinds.td

def err_pragma_stdc_fenv_access_scope : Error<
   "'#pragma STDC FENV_ACCESS' can only appear at file scope or at the start of"
   " a compound statement">;
 def warn_stdc_fenv_round_not_supported :
    Warning<"pragma STDC FENV_ROUND is not supported">,
    InGroup<UnknownPragmas>;
 def warn_stdc_unknown_rounding_mode : Warning<
   "invalid or unsupported rounding mode in '#pragma STDC FENV_ROUND' - ignored">,
   InGroup<IgnoredPragmas>;
+def warn_pragma_fp_ignored : Warning<
+  "'#pragma %0' is not supported on this target - ignored">,
+  InGroup<IgnoredPragmas>;
 // - #pragma comment
 def err_pragma_comment_malformed : Error<
   "pragma comment requires parenthesized identifier and optional string">;
 def err_pragma_comment_unknown_kind : Error<"unknown kind of pragma comment">;
 // PS4 recognizes only #pragma comment(lib)
 def warn_pragma_comment_ignored : Warning<"'#pragma comment %0' ignored">,
   InGroup<IgnoredPragmas>;
 // - #pragma detect_mismatch

clang/lib/Parse/ParsePragma.cpp

 // Pragma STDC implementations.
 
 /// PragmaSTDC_FENV_ACCESSHandler - "\#pragma STDC FENV_ACCESS ...".
 struct PragmaSTDC_FENV_ACCESSHandler : public PragmaHandler {
   PragmaSTDC_FENV_ACCESSHandler() : PragmaHandler("FENV_ACCESS") {}
 
   void HandlePragma(Preprocessor &PP, PragmaIntroducer Introducer,
                     Token &Tok) override {
+    if (!PP.getTargetInfo().hasStrictFP()) {
+      PP.Diag(Tok.getLocation(), diag::warn_pragma_fp_ignored)
+          << "FENV_ACCESS";
+      return;
+    }
     tok::OnOffSwitch OOS;
     if (PP.LexOnOffSwitch(OOS))
      return;
 
     MutableArrayRef<Token> Toks(PP.getPreprocessorAllocator().Allocate<Token>(1),
                                 1);
     Toks[0].startToken();
     Toks[0].setKind(tok::annot_pragma_fenv_access);

 // 'setting' can be: on, off
 /// The optional arguments 'setting' and 'push' are supported only
 /// when the keyword is 'precise' or 'except'.
 void PragmaFloatControlHandler::HandlePragma(Preprocessor &PP,
                                              PragmaIntroducer Introducer,
                                              Token &Tok) {
   Sema::PragmaMsStackAction Action = Sema::PSK_Set;
   SourceLocation FloatControlLoc = Tok.getLocation();
+  if (!PP.getTargetInfo().hasStrictFP()) {
+    PP.Diag(Tok.getLocation(), diag::warn_pragma_fp_ignored)
+        << "float_control";
+    return;
+  }
   PP.Lex(Tok);
   if (Tok.isNot(tok::l_paren)) {
     PP.Diag(FloatControlLoc, diag::err_expected) << tok::l_paren;
     return;
   }
 
   // Read the identifier.
   PP.Lex(Tok);
PP.EnterTokenStream(std::move(TokenArray), TokenList.size(),
                       /*DisableMacroExpansion=*/false, /*IsReinject=*/false);
 }
 
 void PragmaSTDC_FENV_ROUNDHandler::HandlePragma(Preprocessor &PP,
                                                 PragmaIntroducer Introducer,
                                                 Token &Tok) {
   Token PragmaName = Tok;
   SmallVector<Token, 1> TokenList;
+  if (!PP.getTargetInfo().hasStrictFP()) {
+    PP.Diag(Tok.getLocation(), diag::warn_pragma_fp_ignored)
+        << PragmaName.getIdentifierInfo()->getName();
+    return;
+  }
 
   PP.Lex(Tok);
   if (Tok.isNot(tok::identifier)) {
     PP.Diag(Tok.getLocation(), diag::warn_pragma_expected_identifier)
         << PragmaName.getIdentifierInfo()->getName();
     return;
   }
   IdentifierInfo *II = Tok.getIdentifierInfo();

clang/test/Parser/pragma-fp-warn.c

+
+// RUN: %clang_cc1 -triple wasm32 -fsyntax-only -Wno-unknown-pragmas -Wignored-pragmas -verify %s
+// RUN: %clang_cc1 -triple thumbv7 -fsyntax-only -Wno-unknown-pragmas -Wignored-pragmas -verify %s
+// RUN: %clang_cc1 -triple aarch64 -fsyntax-only -Wno-unknown-pragmas -Wignored-pragmas -verify %s
+// RUN: %clang_cc1 -DEXPOK -triple x86_64 -fsyntax-only -Wno-unknown-pragmas -Wignored-pragmas -verify %s
+// RUN: %clang_cc1 -DEXPOK -triple systemz -fsyntax-only -Wno-unknown-pragmas -Wignored-pragmas -verify %s
+// RUN: %clang_cc1 -DEXPOK -triple powerpc -fsyntax-only -Wno-unknown-pragmas -Wignored-pragmas -verify %s
+#ifdef EXPOK
+// expected-no-diagnostics
+#else
+// expected-warning@+8 {{'#pragma FENV_ROUND' is not supported on this target - ignored}}
+// expected-warning@+5 {{'#pragma FENV_ACCESS' is not supported on this target - ignored}}
+// expected-warning@+2 {{'#pragma float_control' is not supported on this target - ignored}}
+#endif
+#pragma float_control(precise, on)
+
+#pragma STDC FENV_ACCESS OFF
+
+#pragma STDC FENV_ROUND FE_DOWNWARD