[PATCH] D72841: [RFC] Add support for pragma float_control, to control precision and exception behavior at the source level

[Melanie Blower via Phabricator via llvm-commits]

mibintc marked 5 inline comments as done.
mibintc added inline comments.


================
Comment at: clang/lib/Sema/SemaExpr.cpp:13129
     if (FunctionDecl *F = dyn_cast<FunctionDecl>(CurContext)) {
+      // If the expression occurs inside an internal global_var_init_function
+      // then the FunctionDecl is not availble
----------------
sepavloff wrote:
> mibintc wrote:
> > sepavloff wrote:
> > > The standard says that static initializers execute in default FP mode.
> > > The standard says ...
> > Are you sure about this one?  Can you please provide the standards reference so I can study it?
> >> The standard says ...
> > Are you sure about this one? Can you please provide the standards reference so I can study it?
> 
> http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf, F.8.5:
> ```
> ... All computation for initialization of objects that have static or thread storage duration is done (as if) at translation time.
> ```
> F.8.2:
> ```
> During translation the IEC 60559 default modes are in effect:
> — The rounding direction mode is rounding to nearest.
> — The rounding precision mode (if supported) is set so that results are not shortened.
> — Trapping or stopping (if supported) is disabled on all floating-point exceptions.
> ```
Thanks for the pointer to the reference. The desired semantics of the pragma may differ from the standard. For example I tried this test case with the fp_contract pragma, and the pragma does modify the semantics of the floating point expressions in the initializer.  So this issue is still a problem in this patch. 

// RUN: %clang_cc1 -emit-llvm -o - %s | FileCheck %s

#pragma STDC FP_CONTRACT ON
float y();
float d();
class ON {
float z = y() * 1 + d();
// CHECK-LABEL: define {{.*}} void @_ZN2ONC2Ev{{.*}}
//CHECK: llvm.fmuladd.f32{{.*}}
};
ON on;

#pragma STDC FP_CONTRACT OFF
class OFF {
float w = y() * 1 + d();
// CHECK-LABEL: define {{.*}} void @_ZN3OFFC2Ev{{.*}}
//CHECK: fmul float
};
OFF off;



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https://reviews.llvm.org/D72841