[PATCH] D104055: Override ffp-contract to fast due to command line changes planned in D74436

[Melanie Blower via Phabricator via llvm-commits]

mibintc added a comment.

In llorg currently, with ffp-model=precise, the option ffp-contract=fast is implied.  My patch to clang is to change this to ffp-contract=on. My patch to LNT hopes to achieve merely "do what you did before so the test has expected behavior".

There could be a problem with my currently proposed LNT patch: it relies on the assumption that the other targets are also building with ffp-model=precise.

My first attempt to patch LNT (submitted Monday) combined with the clang patch modification (submitted Thursday) caused execution time increases on x86 Broadwell.  The clang patch caused LNT fails on other targets because the hash values didn't compare equal.

My current proposal to LNT is to patch the failing tests with ffp-model=precise which hopefully results in no change to LNT results on all targets.

Here's dump of clang cc1 options with ffp-model=precise

bin/clang -### -ffp-model=precise -c test.c >& zot

grep contra zot
 "build/bin/clang-13" "-cc1" "-triple" "x86_64-unknown-linux-gnu" "-emit-obj" "-mrelax-all" "--mrelax-relocations" "-disable-free" "-main-file-name" "test.c" "-mrelocation-model" "static" "-mframe-pointer=all" "-fmath-errno" "-ffp-contract=fast" "-fno-rounding-math" ...


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D104055/new/

https://reviews.llvm.org/D104055