[ubsan] Skip null checks if they are constant-folded away
The IR builder can constant-fold null checks if the pointer operand
points to a constant. If the "is-non-null" check is folded away to
"true", don't emit the null check + branch.
Testing: check-clang, check-ubsan.
This slightly reduces the amount of null checks we emit when compiling
X86ISelLowering.cpp. Here are the numbers from patched/unpatched clangs
based on r300371.
-------------------------------------
| Setup | # of null checks |
-------------------------------------
| unpatched, -O0 | 25251 |
| patched, -O0 | 23925 | (-5.3%)
-------------------------------------
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@300509 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit ebaaf85a35b6e2bd59bc6bfbefb66e7595c751d1)
2 files changed
