Allow use-after-scope front-end argument to take effect with -fsanitize=kernel-address

Lifetime intrinsics required for detection of use-after-scope are not emitted
under kernel-address sanitizer (`-fsanitize=kernel-address`) when paired with
`-O0` & `-fsanitize-address-use-after-scope`.

This is because with `-fsanitize=kernel-address -O0` under
`shouldEmitLifetimeMarkers` in `clang\lib\CodeGen\CodeGenFunction.cpp`,
`CGOpts.SanitizeAddressUseAfterScope` is set to `false`. Therefore, the
following check, `CGOpts.OptimizationLevel != 0`, is run which evaluates to
`false` thus preventing the emission of lifetime markers.

The reason `CGOpts.SanitizeAddressUseAfterScope` is false stems from the fact
that this variable is normally set via the frontend flag
`-fsanitize-address-use-after-scope`, however, this flag only takes effect
under normal address sanitizer due to the gated logic in
`clang\lib\Driver\SanitizerArgs.cpp`, specifically,
`if (AllAddedKinds & SanitizerKind::Address)`. This check excludes
`SanitizerKind::KernelAddress` from consideration, so even if
`-fsanitize-address-use-after-scope` is supplied as a front-end argument, it
won't be passed to `cc1` thus preventing `use-after-scope` checks from
being emitted under `-fsanitize-kernel-address -O0`. Higher optimization levels
will allow emission of lifetime markers regardless thanks to the logic in
`shouldEmitLifetimeMarkers`.

This PR allows `-fsanitize-address-use-after-scope` to take effect under
kernel-address sanitizer.

Author: dgg5503

clang/lib/Driver/SanitizerArgs.cpp

@@ -1099,7 +1099,13 @@ SanitizerArgs::SanitizerArgs(const ToolChain &TC,
     }
 
   } else {
-    AsanUseAfterScope = false;
+    if (AllAddedKinds & SanitizerKind::KernelAddress) {
+      AsanUseAfterScope = Args.hasFlag(
+          options::OPT_fsanitize_address_use_after_scope,
+          options::OPT_fno_sanitize_address_use_after_scope, AsanUseAfterScope);
+    } else {
+      AsanUseAfterScope = false;
+    }
     // -fsanitize=pointer-compare/pointer-subtract requires -fsanitize=address.
     SanitizerMask DetectInvalidPointerPairs =
         SanitizerKind::PointerCompare | SanitizerKind::PointerSubtract;

clang/test/CodeGen/lifetime-sanitizer.c

@@ -4,6 +4,9 @@
 // RUN:     -fsanitize=address -fsanitize-address-use-after-scope \
 // RUN:     -Xclang -disable-llvm-passes %s | FileCheck %s -check-prefix=LIFETIME
 // RUN: %clang -target x86_64-linux-gnu -S -emit-llvm -o - -O0 \
+// RUN:     -fsanitize=kernel-address -fsanitize-address-use-after-scope \
+// RUN:     -Xclang -disable-llvm-passes %s | FileCheck %s -check-prefix=LIFETIME
+// RUN: %clang -target x86_64-linux-gnu -S -emit-llvm -o - -O0 \
 // RUN:     -fsanitize=memory -Xclang -disable-llvm-passes %s | \
 // RUN:     FileCheck %s -check-prefix=LIFETIME
 // RUN: %clang -target aarch64-linux-gnu -S -emit-llvm -o - -O0 \

clang/test/CodeGenCXX/lifetime-sanitizer.cpp

@@ -5,6 +5,9 @@
 // RUN:     -fsanitize=address -fsanitize-address-use-after-scope \
 // RUN:     -Xclang -disable-llvm-passes %s | FileCheck %s -check-prefixes=CHECK,LIFETIME
 // RUN: %clang -w -target x86_64-linux-gnu -S -emit-llvm -o - -fno-exceptions -O0 \
+// RUN:     -fsanitize=kernel-address -fsanitize-address-use-after-scope \
+// RUN:     -Xclang -disable-llvm-passes %s | FileCheck %s -check-prefixes=CHECK,LIFETIME
+// RUN: %clang -w -target x86_64-linux-gnu -S -emit-llvm -o - -fno-exceptions -O0 \
 // RUN:     -fsanitize=memory -Xclang -disable-llvm-passes %s | \
 // RUN:     FileCheck %s -check-prefixes=CHECK,LIFETIME
 // RUN: %clang -w -target aarch64-linux-gnu -S -emit-llvm -o - -fno-exceptions -O0 \