[clang] [Clang][SYCL] Introduce clang-sycl-linker to link SYCL offloading device code (Part 1 of many) (PR #112245)

[Joseph Huber via cfe-commits]

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+// Tests the clang-sycl-linker tool.
+//
+// Test a simple case without arguments.
+// RUN: %clangxx -fsycl -emit-llvm -c %s -o %t.bc
+// RUN: clang-sycl-linker --dry-run -triple spirv64 %t.bc -o a.spv 2>&1 \
+// RUN:   | FileCheck %s --check-prefix=SIMPLE
+// SIMPLE: "{{.*}}llvm-link{{.*}}" {{.*}}.bc -o [[FIRSTLLVMLINKOUT:.*]].bc --suppress-warnings
+// SIMPLE-NEXT: "{{.*}}llvm-spirv{{.*}}" {{.*}}-o a.spv [[FIRSTLLVMLINKOUT]].bc
+//
+// Test a simple case with device library files specified.
+// RUN: echo ' ' > %T/lib1.bc
+// RUN: echo ' ' > %T/lib2.bc
+// RUN: clang-sycl-linker --dry-run -triple spirv64 %t.bc --library-path=%T --device-libs=lib1.bc,lib2.bc -o a.spv 2>&1 \
+// RUN:   | FileCheck %s --check-prefix=DEVLIBS
+// DEVLIBS: "{{.*}}llvm-link{{.*}}" {{.*}}.bc -o [[FIRSTLLVMLINKOUT:.*]].bc --suppress-warnings
+// DEVLIBS-NEXT: "{{.*}}llvm-link{{.*}}" -only-needed [[FIRSTLLVMLINKOUT]].bc {{.*}}lib1.bc {{.*}}lib2.bc -o [[SECONDLLVMLINKOUT:.*]].bc --suppress-warnings
+// DEVLIBS-NEXT: "{{.*}}llvm-spirv{{.*}}" {{.*}}-o a.spv [[SECONDLLVMLINKOUT]].bc
+//
+// Test a simple case with .o (fat object) as input.
+// TODO: Remove this test once fat object support is added.
----------------
jhuber6 wrote:

Yes, that's correct. Currently trying to make the linker wrapper a bit leaner, but the expected flow should be
```
fatbin.o -> dev1.o, dev2.o
  - clang --target=TRIPLE -o image dev1.o dev2.o
```
My general assertion is that every target should have a way to get a usable image via a `clang --target` invocation, which should be equipped to handle normal linker stuff.

https://github.com/llvm/llvm-project/pull/112245