Provide PTXLinker with fallback to internal target-cpu

Author: denzp

src/ci/docker/test-various/Dockerfile

@@ -14,7 +14,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
   xz-utils
 
 # FIXME: build the `ptx-linker` instead.
-RUN curl -sL https://github.com/denzp/rust-ptx-linker/releases/download/v0.9.0-alpha.1/rust-ptx-linker.linux64.tar.gz | \
+RUN curl -sL https://github.com/denzp/rust-ptx-linker/releases/download/v0.9.0-alpha.2/rust-ptx-linker.linux64.tar.gz | \
   tar -xzvC /usr/bin
 
 RUN curl -sL https://nodejs.org/dist/v9.2.0/node-v9.2.0-linux-x64.tar.xz | \

src/librustc_codegen_ssa/back/linker.rs

@@ -1132,6 +1132,12 @@ impl<'a> Linker for PtxLinker<'a> {
     }
 
     fn finalize(&mut self) -> Command {
+        // Provide the linker with fallback to internal `target-cpu`.
+        self.cmd.arg("--fallback-arch").arg(match self.sess.opts.cg.target_cpu {
+            Some(ref s) => s,
+            None => &self.sess.target.target.options.cpu
+        });
+
         ::std::mem::replace(&mut self.cmd, Command::new(""))
     }
 

src/test/run-make/nvptx-binary-crate/Makefile

@@ -2,8 +2,11 @@
 
 ifeq ($(TARGET),nvptx64-nvidia-cuda)
 all:
-	$(RUSTC) main.rs -Clink-arg=--arch=sm_60 --crate-type="bin" -O --target $(TARGET)
-	FileCheck main.rs --input-file $(TMPDIR)/main.ptx
+	$(RUSTC) main.rs --crate-type="bin" --target $(TARGET) -O -C link-arg=--arch=sm_60 -o $(TMPDIR)/main.link_arg.ptx
+	$(RUSTC) main.rs --crate-type="bin" --target $(TARGET) -O -C target-cpu=sm_60 -o $(TMPDIR)/main.target_cpu.ptx
+
+	FileCheck main.rs --input-file $(TMPDIR)/main.link_arg.ptx
+	FileCheck main.rs --input-file $(TMPDIR)/main.target_cpu.ptx
 else
 all:
 endif

src/test/run-make/nvptx-dylib-crate/kernel.rs

@@ -5,7 +5,7 @@
 extern crate dep;
 
 // Verify the default CUDA arch.
-// CHECK: .target sm_20
+// CHECK: .target sm_30
 // CHECK: .address_size 64
 
 // Make sure declarations are there.