This PR removes tests with `br i1 undef` under
`llvm/tests/Transforms/HotColdSplit` and `llvm/tests/Transforms/I*`.

Reviewers: vsk, eli.friedman, yassingh

Differential Revision: https://reviews.llvm.org/D158937

This broke Chromium's PGO build, it seems because hot-cold-splitting got turned
on unintentionally. See comment on the code review for repro etc.

> This patch adds -f[no-]split-cold-code CC1 options to clang. This allows
> the splitting pass to be toggled on/off. The current method of passing
> `-mllvm -hot-cold-split=true` to clang isn't ideal as it may not compose
> correctly (say, with `-O0` or `-Oz`).
>
> To implement the -fsplit-cold-code option, an attribute is applied to
> functions to indicate that they may be considered for splitting. This
> removes some complexity from the old/new PM pipeline builders, and
> behaves as expected when LTO is enabled.
>
> Co-authored by: Saleem Abdulrasool <compnerd@compnerd.org>
> Differential Revision: https://reviews.llvm.org/D57265
> Reviewed By: Aditya Kumar, Vedant Kumar
> Reviewers: Teresa Johnson, Aditya Kumar, Fedor Sergeev, Philip Pfaffe, Vedant Kumar

This reverts commit 273c299d5d649a0222fbde03c9a41e41913751b4.

This patch adds -f[no-]split-cold-code CC1 options to clang. This allows
the splitting pass to be toggled on/off. The current method of passing
`-mllvm -hot-cold-split=true` to clang isn't ideal as it may not compose
correctly (say, with `-O0` or `-Oz`).

To implement the -fsplit-cold-code option, an attribute is applied to
functions to indicate that they may be considered for splitting. This
removes some complexity from the old/new PM pipeline builders, and
behaves as expected when LTO is enabled.

Co-authored by: Saleem Abdulrasool <compnerd@compnerd.org>
Differential Revision: https://reviews.llvm.org/D57265
Reviewed By: Aditya Kumar, Vedant Kumar
Reviewers: Teresa Johnson, Aditya Kumar, Fedor Sergeev, Philip Pfaffe, Vedant Kumar

The reversion apparently deleted the test/Transforms directory.

Will be re-reverting again.

llvm-svn: 358552

As it's causing some bot failures (and per request from kbarton).

This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.

llvm-svn: 358546

The main goal of the model is to avoid *increasing* function size, as
that would eradicate any memory locality benefits from splitting. This
happens when:

  - There are too many inputs or outputs to the cold region. Argument
    materialization and reloads of outputs have a cost.

  - The cold region has too many distinct exit blocks, causing a large
    switch to be formed in the caller.

  - The code size cost of the split code is less than the cost of a
    set-up call.

A secondary goal is to prevent excessive overall binary size growth.

With the cost model in place, I experimented to find a splitting
threshold that works well in practice. To make warm & cold code easily
separable for analysis purposes, I moved split functions to a "cold"
section. I experimented with thresholds between [0, 4] and set the
default to the threshold which minimized geomean __text size.

Experiment data from building LNT+externals for X86 (N = 639 programs,
all sizes in bytes):

| Configuration | __text geom size | __cold geom size | TEXT geom size |
| **-Os**       | 1736.3           | 0, n=0           | 10961.6        |
| -Os, thresh=0 | 1740.53          | 124.482, n=134   | 11014          |
| -Os, thresh=1 | 1734.79          | 57.8781, n=90    | 10978.6        |
| -Os, thresh=2 | ** 1733.85 **    | 65.6604, n=61    | 10977.6        |
| -Os, thresh=3 | 1733.85          | 65.3071, n=61    | 10977.6        |
| -Os, thresh=4 | 1735.08          | 67.5156, n=54    | 10965.7        |
| **-Oz**       | 1554.4           | 0, n=0           | 10153          |
| -Oz, thresh=2 | ** 1552.2 **     | 65.633, n=61     | 10176          |
| **-O3**       | 2563.37          | 0, n=0           | 13105.4        |
| -O3, thresh=2 | ** 2559.49 **    | 71.1072, n=61    | 13162.4        |

Picking thresh=2 reduces the geomean __text section size by 0.14% at
-Os, -Oz, and -O3 and causes ~0.2% growth in the TEXT segment. Note that
TEXT size is page-aligned, whereas section sizes are byte-aligned.

Experiment data from building LNT+externals for ARM64 (N = 558 programs,
all sizes in bytes):

| Configuration | __text geom size | __cold geom size | TEXT geom size |
| **-Os**       | 1763.96          | 0, n=0           | 42934.9        |
| -Os, thresh=2 | ** 1760.9 **     | 76.6755, n=61    | 42934.9        |

Picking thresh=2 reduces the geomean __text section size by 0.17% at
-Os and causes no growth in the TEXT segment.

Measurements were done with D57082 (r352080) applied.

Differential Revision: https://reviews.llvm.org/D57125

llvm-svn: 352228

This gets rid of the brittle/mysterious calls to @sink()/@sideeffect()
peppered throughout the test cases. They are no longer needed to force
splitting to occur.

llvm-svn: 351480