Changes

[Driver] Perform Linux distribution detection only once

Differential Revision: https://reviews.llvm.org/D87187

[Driver] Fix formatting as suggested by clang-format (NFC)

[SelectionDAG] Add guard to automatically insert flags

This is like FastMathFlagGuard in IR. Since we use SDAG instance to get
values, it's with SelectionDAG. By creating a FlagInserter in current
scope, all values created by getNode will get the flags if no Flags
argument provided.

In this patch, I applied it to floating point operations folding part in
DAG combiner, and removed Flags passing to getNode to show its effect.
Other places in DAG combiner and other helper methods similar to getNode
also need this. They can be done in follow-up patches.

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D87361

[CodeGen] Do not call `emitGlobalConstantLargeInt` for constant requires 8 bytes to store

This is a fix for PR47630. The regression is caused by the D78011. After
this change the code starts to call the `emitGlobalConstantLargeInt` even
for constants which requires eight bytes to store.

Differential revision: https://reviews.llvm.org/D88261

[LoopDelete][Assume] Allow deleting loops with assumes

This pervent very poor optimization caused by a signle assume like https://godbolt.org/z/EK3oMh

baseline flags: -O3
patched flags: -O3 -mllvm --enable-knowledge-retention

Before the patch
```
Metric: compile_time
Program                                                      baseline patched diff
             test-suite :: CTMark/tramp3d-v4/tramp3d-v4.test  20.72    29.74  43.5%
                     test-suite :: CTMark/Bullet/bullet.test  24.39    24.91   2.2%
               test-suite :: CTMark/7zip/7zip-benchmark.test  37.39    38.06   1.8%
                      test-suite :: CTMark/kimwitu++/kc.test  11.76    11.94   1.5%
                   test-suite :: CTMark/sqlite3/sqlite3.test  12.94    12.91  -0.3%
                       test-suite :: CTMark/SPASS/SPASS.test  11.72    11.70  -0.2%
                     test-suite :: CTMark/lencod/lencod.test  16.12    16.10  -0.1%
                   test-suite :: CTMark/ClamAV/clamscan.test  13.31    13.30  -0.1%
              test-suite :: CTMark/mafft/pairlocalalign.test   9.12     9.12  -0.1%
 test-suite :: CTMark/consumer-typeset/consumer-typeset.test   9.34     9.34  -0.1%
                                          Geomean difference                   4.2%

Metric: compiler_Kinst_count
Program                                                      baseline     patched      diff
             test-suite :: CTMark/tramp3d-v4/tramp3d-v4.test 107576069.87 172886418.90 60.7%
                     test-suite :: CTMark/Bullet/bullet.test 123291865.66 125457117.96  1.8%
                      test-suite :: CTMark/kimwitu++/kc.test  56347884.64  57298544.14  1.7%
               test-suite :: CTMark/7zip/7zip-benchmark.test 180637699.58 183341656.57  1.5%
                   test-suite :: CTMark/sqlite3/sqlite3.test  66723788.85  66664692.80 -0.1%
                   test-suite :: CTMark/ClamAV/clamscan.test  69581500.56  69597863.92  0.0%
                     test-suite :: CTMark/lencod/lencod.test  94236501.48  94216545.32 -0.0%
                       test-suite :: CTMark/SPASS/SPASS.test  58516756.95  58505089.07 -0.0%
 test-suite :: CTMark/consumer-typeset/consumer-typeset.test  48832815.53  48841989.39  0.0%
              test-suite :: CTMark/mafft/pairlocalalign.test  49682720.53  49686324.34  0.0%
                                          Geomean difference                            5.4%
```

After the patch
```
Metric: compile_time
Program                                                      baseline patched diff
             test-suite :: CTMark/tramp3d-v4/tramp3d-v4.test  20.70    22.40   8.2%
               test-suite :: CTMark/7zip/7zip-benchmark.test  37.13    38.05   2.5%
                     test-suite :: CTMark/Bullet/bullet.test  24.25    24.83   2.4%
                      test-suite :: CTMark/kimwitu++/kc.test  11.69    11.94   2.2%
                   test-suite :: CTMark/ClamAV/clamscan.test  13.19    13.36   1.3%
                     test-suite :: CTMark/lencod/lencod.test  16.02    16.19   1.1%
 test-suite :: CTMark/consumer-typeset/consumer-typeset.test   9.29     9.36   0.7%
                       test-suite :: CTMark/SPASS/SPASS.test  11.64    11.73   0.7%
              test-suite :: CTMark/mafft/pairlocalalign.test   9.10     9.15   0.5%
                   test-suite :: CTMark/sqlite3/sqlite3.test  12.95    12.96   0.0%
                                          Geomean difference                   1.9%

Metric: compiler_Kinst_count
Program                                                      baseline     patched      diff
             test-suite :: CTMark/tramp3d-v4/tramp3d-v4.test 107590933.61 114044834.72  6.0%
                      test-suite :: CTMark/kimwitu++/kc.test  56344526.77  57235806.29  1.6%
                     test-suite :: CTMark/Bullet/bullet.test 123291285.10 125128334.97  1.5%
               test-suite :: CTMark/7zip/7zip-benchmark.test 180641540.10 183155706.39  1.4%
                   test-suite :: CTMark/sqlite3/sqlite3.test  66725619.22  66668713.92 -0.1%
                       test-suite :: CTMark/SPASS/SPASS.test  58509029.85  58478704.75 -0.1%
 test-suite :: CTMark/consumer-typeset/consumer-typeset.test  48843711.23  48826894.68 -0.0%
                     test-suite :: CTMark/lencod/lencod.test  94233305.79  94207544.23 -0.0%
                   test-suite :: CTMark/ClamAV/clamscan.test  69587887.66  69603549.90  0.0%
              test-suite :: CTMark/mafft/pairlocalalign.test  49686968.65  49689291.04  0.0%
                                          Geomean difference                            1.0%
```

Reviewed By: jdoerfert, efriedma

Differential Revision: https://reviews.llvm.org/D86816