[PATCH] D39611: [CodeGen] make cbrt and fma constant (never set errno); document complex calls as always constant

[Sanjay Patel via Phabricator via cfe-commits]

spatel created this revision.
Herald added a subscriber: mcrosier.

These are 3 errno-related diffs raised in D39841.

1. Cube root

We're going to dismiss POSIX language like this:
"On successful completion, cbrt() returns the cube root of x. If x is NaN, cbrt() returns NaN and errno may be set to [EDOM]. "
http://pubs.opengroup.org/onlinepubs/7908799/xsh/cbrt.html

And favor an interpretation based on the C standard that says:
"Functions with a NaN argument return a NaN result and raise no floating-point exception, except where stated otherwise."

2. Floating multiply-add

The C standard is silent?
http://pubs.opengroup.org/onlinepubs/9699919799/functions/fma.html - clearly says "...then errno shall be set..."
but:
https://linux.die.net/man/3/fma - "These functions do not set errno."

Let's opt for the - hopefully common - implementation where errno is not set. Note that there's no test change because as noted in the earlier discussion, we're ignoring the const attr in CodeGenFunction::EmitBuiltinExpr(). I'll look at what needs fixing in that function next.

3. Complex

This is came up specifically for 'carg', but I'm hoping we can use 1 justification for the whole lib.

The POSIX docs all have language like this for complex calls:
"No errors are defined."
http://pubs.opengroup.org/onlinepubs/9699919799/functions/ccos.html

The lack of errno handling is allowed by the inclusion of "optionally" in the C standard definitions of all of the complex ops?
"csqrt(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-point exception, for finite x"


https://reviews.llvm.org/D39611

Files:
  include/clang/Basic/Builtins.def
  test/CodeGen/builtin-errno.c
  test/CodeGen/libcalls-errno.c

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