Re-roll clang llvmorg-12-init-5035-gd0abc757-3 : llvmorg-12-init-5627-gf086e85e-1.

The rolled-to clang has a broken feature that's enabled by default.
We disable that feature by passing -mllvm -enable-dse-memoryssa=false.

In the first CL, we only passed that in cflags, which is normally
enough. However, in LTO builds the flag must be present at link time,
so the reland adds it to ldflags as well.

(On the ToT bots, we force enable-dse-memoryssa to true to check that
the problems with the feature are fixed at clang trunk. Don't do this
in thinlto builds -- we don't have any tot thinlto bots that run tests
anyway.)

Bug: 1128966,1128144,1126953
Change-Id: I214b31bd35560d705071e4583df7b019e9f96691
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2446093
Commit-Queue: Nico Weber <thakis@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Auto-Submit: Nico Weber <thakis@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813334}

build/config/compiler/BUILD.gn

@@ -625,6 +625,9 @@ config("compiler") {
         # Experimentally determined to yield a reasonable trade-off between
         # build time, run-time performance, and binary size.
         "-mllvm:-import-instr-limit=10",
+
+        # TODO(https://crbug.com/1127713): Investigate, remove.
+        "-mllvm:-enable-dse-memoryssa=false",
       ]
     } else {
       ldflags += [ "-flto=thin" ]
@@ -648,6 +651,9 @@ config("compiler") {
         "-Wl,--thinlto-cache-policy,$cache_policy",
       ]
 
+      # TODO(https://crbug.com/1127713): Investigate, remove.
+      ldflags += [ "-Wl,-mllvm,-enable-dse-memoryssa=false" ]
+
       ldflags += [ "-Wl,--lto-O" + lto_opt_level ]
       if (thin_lto_enable_optimizations) {
         if (is_android) {

tools/clang/scripts/update.py

@@ -38,8 +38,8 @@ import zipfile
 # https://chromium.googlesource.com/chromium/src/+/master/docs/updating_clang.md
 # Reverting problematic clang rolls is safe, though.
 # This is the output of `git describe` and is usable as a commit-ish.
-CLANG_REVISION = 'llvmorg-12-init-5035-gd0abc757'
-CLANG_SUB_REVISION = 3
+CLANG_REVISION = 'llvmorg-12-init-5627-gf086e85e'
+CLANG_SUB_REVISION = 2
 
 PACKAGE_VERSION = '%s-%s' % (CLANG_REVISION, CLANG_SUB_REVISION)
 RELEASE_VERSION = '12.0.0'