There are currently two options that are used to tell the compiler to perform
unsafe floating-point optimizations:
'-ffast-math' and '-funsafe-math-optimizations'.

'-ffast-math' is enabled by default. It automatically enables the driver option
'-menable-unsafe-fp-math'.
Below is a table illustrating the special operations enabled automatically by
'-ffast-math', '-funsafe-math-optimizations' and '-menable-unsafe-fp-math'
respectively.

Special Operations -ffast-math	-funsafe-math-optimizations -menable-unsafe-fp-math
MathErrno	       0	         1	                    1
FiniteMathOnly         1 	         0                          0
AllowFPReassoc	       1         	 1                          1
NoSignedZero	       1                 1                          1
AllowRecip             1                 1                          1
ApproxFunc             1                 1                          1
RoundingMath	       0                 0                          0
UnsafeFPMath	       1                 0                          1
FPContract	       fast	         on	                    on

'-ffast-math' enables '-fno-math-errno', '-ffinite-math-only',
'-funsafe-math-optimzations' and sets 'FpContract' to 'fast'. The driver option
'-menable-unsafe-fp-math' enables the same special options than
'-funsafe-math-optimizations'. This is redundant.
We propose to remove the driver option '-menable-unsafe-fp-math' and use
instead, the setting of the special operations to set the function attribute
'unsafe-fp-math'. This attribute will be enabled only if those special
operations are enabled and if 'FPContract' is either 'fast' or set to the
default value.

Differential Revision: https://reviews.llvm.org/D135097

Currently, we prohibit this pragma from appearing within a language
linkage specification, but this is useful functionality that is
supported by MSVC (which is where we inherited this feature from).
This patch allows you to use the pragma within an extern "C" {} (etc)
block.

This patch removes the -f[no-]trapping-math flags from the -cc1 command line. These flags are ignored in the command line parser and their semantics is fully handled by -ffp-exception-mode.

This patch does not remove -f[no-]trapping-math from the driver command line. The driver flags are being used and do affect compilation.

Reviewed By: dexonsmith, SjoerdMeijer

Differential Revision: https://reviews.llvm.org/D93395

Reviewers: rjmccall, rsmith, sepavloff

Differential Revision: https://reviews.llvm.org/D87528

Summary: Erroneous error diagnostic observed in VS2017 <numeric> header
Also correction to propagate usesFPIntrin from template func to instantiation.

Reviewers: rjmccall, erichkeane (no feedback received)

Differential Revision: https://reviews.llvm.org/D79631

Bug reported by @uabelho against reviews.llvm.org/D72841

Reviewers: rjmccall

Differential Revision: https://reviews.llvm.org/D79510

Add support for #pragma float_control

Reviewers: rjmccall, erichkeane, sepavloff

Differential Revision: https://reviews.llvm.org/D72841

This reverts commit fce82c0ed310174fe48e2402ac731b6340098389.

This reverts commit 69aacaf699922ffe0450f567e21208c10c84731f.

test cases
Add support for #pragma float_control

Reviewers: rjmccall, erichkeane, sepavloff

Differential Revision: https://reviews.llvm.org/D72841

This reverts commit 85dc033caccaa6ab919d57f9759290be41240146, and makes
corrections to the test cases that failed on buildbots.

This reverts commit 4f1e9a17e9d28bdfd035313c96b3a5d4c91a7733.
due to fail on buildbot, sorry for the noise