[DTLTO] Add remote compiler option forwarding coverage (#208589)

Add a cross-project DTLTO test that checks the existing LTO
configuration state serialized into the remote Clang command line. The
test uses the validate.py distributor to inspect the generated DTLTO
JSON.

Cover all the existing forwarded options.

Add paired negative checks for optional flags so the test also verifies
they are not emitted when the corresponding configuration state is not
set.

cross-project-tests/CMakeLists.txt

@@ -26,6 +26,7 @@ set(CROSS_PROJECT_TEST_DEPS
   llvm-config
   llvm-dis
   llvm-dwarfdump
+  llvm-lto2
   llvm-modextract
   llvm-objdump
   not

cross-project-tests/dtlto/remote-options.test

@@ -0,0 +1,90 @@
+REQUIRES: ld.lld
+
+## Check that DTLTO passes LTO configuration to the remote Clang via the
+## command line.
+
+RUN: rm -rf %t && split-file %s %t && cd %t
+
+RUN: %clang --target=x86_64-unknown-linux-gnu -flto=thin -c test.c -o elf.o
+RUN: %clang --target=x86_64-pc-windows-msvc -flto=thin -c test.c -o coff.o
+RUN: touch profile.prof
+
+## The validate.py distributor prints the DTLTO JSON and then exits without
+## producing native objects, so each llvm-lto2 command is expected to fail after
+## the JSON has been emitted.
+DEFINE: %{base} = not llvm-lto2 run \
+DEFINE:   -dtlto-distributor=%python \
+DEFINE:   -dtlto-distributor-arg=%llvm_src_root/utils/dtlto/validate.py \
+DEFINE:   -dtlto-compiler=%clang \
+DEFINE:   -o test.out
+
+DEFINE: %{lld} = not ld.lld elf.o \
+DEFINE:   --thinlto-distributor=%python \
+DEFINE:   --thinlto-distributor-arg=%llvm_src_root/utils/dtlto/validate.py \
+DEFINE:   --thinlto-remote-compiler=%clang \
+DEFINE:   -o test.elf
+
+DEFINE: %{lto2-elf} = %{base} elf.o -r=elf.o,foo,px
+DEFINE: %{lto2-coff} = %{base} coff.o -r=coff.o,foo,px
+
+ARGS: "args": [
+
+## Optimization level.
+RUN: %{lto2-elf} -O0 2>&1 | FileCheck %s --check-prefixes=ARGS,O0,ERR
+RUN: %{lto2-elf} -O3 2>&1 | FileCheck %s --check-prefixes=ARGS,O3,ERR
+O0: "-O0"
+O3: "-O3"
+
+## Address-significance table, function sections, and data sections.
+RUN: %{lto2-elf} -addrsig -function-sections -data-sections 2>&1 | \
+RUN:   FileCheck %s --check-prefixes=ARGS,SECTIONS,ERR
+SECTIONS: "-faddrsig"
+SECTIONS: "-ffunction-sections"
+SECTIONS: "-fdata-sections"
+
+RUN: %{lto2-elf} 2>&1 | FileCheck %s --check-prefixes=ARGS,NO-SECTIONS,ERR
+NO-SECTIONS-NOT: "-faddrsig"
+NO-SECTIONS-NOT: "-ffunction-sections"
+NO-SECTIONS-NOT: "-fdata-sections"
+
+## PIC is forwarded as -fpic for ELF targets but not for COFF targets because
+## Clang does not accept -fpic for every target.
+RUN: %{lto2-elf} -relocation-model=pic 2>&1 | \
+RUN:   FileCheck %s --check-prefixes=ARGS,PIC,ERR
+PIC: "-fpic"
+
+RUN: %{lto2-elf} -relocation-model=static 2>&1 | \
+RUN:   FileCheck %s --check-prefixes=ARGS,NO-PIC,ERR
+NO-PIC-NOT: "-fpic"
+
+RUN: %{lto2-coff} -relocation-model=pic 2>&1 | \
+RUN:   FileCheck %s --check-prefixes=COFF-PIC,ERR
+COFF-PIC-NOT: "-fpic"
+
+## Sample profile forwarding and common-input serialization.
+RUN: %{lto2-elf} -lto-sample-profile-file=profile.prof 2>&1 | \
+RUN:   FileCheck %s --check-prefixes=ARGS,SAMPLE,ERR
+SAMPLE: "-fprofile-sample-use=profile.prof"
+SAMPLE: "inputs": [
+SAMPLE: "profile.prof"
+
+RUN: %{lto2-elf} 2>&1 | FileCheck %s --check-prefixes=ARGS,NO-SAMPLE,ERR
+NO-SAMPLE-NOT: "-fprofile-sample-use=profile.prof"
+NO-SAMPLE-NOT: "profile.prof"
+
+## PGO warning mismatch control is an LLD-driver option rather than an
+## llvm-lto2 option, so check it through the ELF linker.
+RUN: %{lld} --no-lto-pgo-warn-mismatch 2>&1 | \
+RUN:   FileCheck %s --check-prefixes=ARGS,PGO-WARN,ERR
+PGO-WARN: "-mllvm"
+PGO-WARN-NEXT: "-no-pgo-warn-mismatch"
+
+RUN: %{lld} 2>&1 | \
+RUN:   FileCheck %s --check-prefixes=ARGS,NO-PGO-WARN,ERR
+NO-PGO-WARN-NOT: "-no-pgo-warn-mismatch"
+
+## Check for the expected error from the use of validate.py.
+ERR: DTLTO backend compilation: cannot open native object file:
+
+#--- test.c
+void foo(void) {}