Previously #pragma STDC FENV_ACCESS ON always set dynamic rounding
mode and strict exception handling. It is not correct in the presence
of other pragmas that also modify rounding mode and exception handling.
For example, the effect of previous pragma FENV_ROUND could be
cancelled, which is not conformant with the C standard. Also
#pragma STDC FENV_ACCESS OFF turned off only FEnvAccess flag, leaving
rounding mode and exception handling unchanged, which is incorrect in
general case.
Concrete rounding and exception mode depend on a combination of several
factors like various pragmas and command-line options. During the review
of this patch an idea was proposed that the semantic actions associated
with such pragmas should only set appropriate flags. Actual rounding
mode and exception handling should be calculated taking into account the
state of all relevant options. In such implementation the pragma
FENV_ACCESS should not override properties set by other pragmas but
should set them if such setting is absent.
To implement this approach the following main changes are made:
- Field FPRoundingMode is removed from LangOptions. Actually there are no options that set it to arbitrary rounding mode, the choice was only dynamic or tonearest. Instead, a new boolean flag RoundingMath is added, with the same meaning as the corresponding command-line option.
- Type FPExceptionModeKind now has possible value FPE_Default. It does not represent any particular exception mode but indicates that such mode was not set and default value should be used. It allows to distinguish the case:
{ #pragma STDC FENV_ACCESS ON ... }
where the pragma must set FPE_Strict, from the case:
{ #pragma clang fp exceptions(ignore) #pragma STDC FENV_ACCESS ON ... }
where exception mode should remain FPE_Ignore.- Class FPOptions has now methods getRoundingMode and getExceptionMode, which calculates the respective properties from other specified FP properties.
- Class LangOptions has now methods getDefaultRoundingMode and getDefaultExceptionMode, which calculates default modes from the specified options and should be used instead of getRoundingMode and getFPExceptionMode of the same class.
I'm suggesting this should be setRoundingMode(llvm::RoundingMode::Dynamic).
If FENV_ACCESS is off, getEffectiveRoundingMode() converts that to "nearest". If FENV_ACCESS is turned on, the mode is treated as dynamic. This is exactly what we want.