[PATCH] When pragma FENV_ACCESS is ignored do not modify Sema.CurFPFeatures

[mibintc]

Summary

Bug reported by @uabelho against reviews.llvm.org/D72841
pragma STDC FENV_ACCESS ON is ignored, but the floating point state maintained in Sema.CurFPFeatures was modified to show that
fenv_access was enabled, this caused llvm constrained intrinsics to be created which is erroneous. This is a small patch to avoid modifying the state.

[mibintc]

clang/lib/Parse/ParsePragma.cpp

111

Modified this to return instead of making changes which will ultimately modify the floating point state

clang/test/CodeGen/fp-floatcontrol-pragma.cpp

61

I used a modified version of @uabelho 's test. I verified that before this bug fix a constrained intrinsic was being created for this multiply.

[rjmccall]

LGTM

[uabelho]

Great! Thanks!

clang/lib/Parse/ParsePragma.cpp

struct PragmaSTDC_FENV_ACCESSHandler : public PragmaHandler {
 
   void HandlePragma(Preprocessor &PP, PragmaIntroducer Introducer,
                     Token &Tok) override {
     tok::OnOffSwitch OOS;
     if (PP.LexOnOffSwitch(OOS))
      return;
     if (OOS == tok::OOS_ON) {
       PP.Diag(Tok, diag::warn_stdc_fenv_access_not_supported);
+      return;
     }
 
     MutableArrayRef<Token> Toks(PP.getPreprocessorAllocator().Allocate<Token>(1),
                                 1);
     Toks[0].startToken();
     Toks[0].setKind(tok::annot_pragma_fenv_access);
     Toks[0].setLocation(Tok.getLocation());
     Toks[0].setAnnotationEndLoc(Tok.getLocation());

clang/test/CodeGen/fp-floatcontrol-pragma.cpp

 // RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -verify -DFENV_ON=1 -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck %s
 
 float fff(float x, float y) {
 // CHECK-LABEL: define float @_Z3fffff{{.*}}
 // CHECK: entry
 #pragma float_control(except, on)
   float z;
   z = z * z;
   //CHECK: llvm.experimental.constrained.fmul{{.*}}
#pragma float_control(precise, on)
   {
 #pragma float_control(precise, off)
     z = x * y + z;
     //CHECK: fmul fast float
     //CHECK: fadd fast float
   }
   return z;
 }
+
 float fma_test1(float a, float b, float c) {
 // CHECK-LABEL define float @_Z9fma_test1fff{{.*}}
 #pragma float_control(precise, on)
   float x = a * b + c;
   //CHECK: fmuladd
   return x;
 }
+
+#if FENV_ON
+// expected-warning@+1{{pragma STDC FENV_ACCESS ON is not supported, ignoring pragma}}
+#pragma STDC FENV_ACCESS ON
+#endif
+// CHECK-LABEL: define {{.*}}callt{{.*}}
+
+void callt() {
+  volatile float z;
+  z = z * z;
+//CHECK: = fmul float
+}

clang/test/Parser/fp-floatcontrol-syntax.cpp

 // RUN: %clang_cc1 -triple x86_64-linux-gnu -menable-no-infs -menable-no-nans -menable-unsafe-fp-math -fno-signed-zeros -mreassociate -freciprocal-math -ffp-contract=fast -ffast-math -ffinite-math-only -fsyntax-only %s -DFAST -verify
 double a = 0.0;
 double b = 1.0;
 
 //FIXME At some point this warning will be removed, until then
 //      document the warning
 #ifdef FAST
 // expected-warning@+1{{pragma STDC FENV_ACCESS ON is not supported, ignoring pragma}}
-#pragma STDC FENV_ACCESS ON // expected-error{{'#pragma STDC FENV_ACCESS ON' is illegal when precise is disabled}}
+#pragma STDC FENV_ACCESS ON
 #else
 #pragma STDC FENV_ACCESS ON // expected-warning{{pragma STDC FENV_ACCESS ON is not supported, ignoring pragma}}
 #endif
 #ifdef STRICT
 #pragma float_control(precise, off) // expected-error {{'#pragma float_control(precise, off)' is illegal when except is enabled}}
 #else
-#pragma float_control(precise, off) // expected-error {{'#pragma float_control(precise, off)' is illegal when fenv_access is enabled}}
+// Currently FENV_ACCESS cannot be enabled by pragma, skip error check
+#pragma float_control(precise, off) // not-expected-error {{'#pragma float_control(precise, off)' is illegal when fenv_access is enabled}}
 #endif
 
 #pragma float_control(precise, on)
 #pragma float_control(except, on) // OK
 #ifndef STRICT
 #pragma float_control(except, on)
 #pragma float_control(precise, off) // expected-error {{'#pragma float_control(precise, off)' is illegal when except is enabled}}
 #endif