Header file to help forcibly link GPURuntime

[singam-sanjay]

Summary

LinkGPURuntime.h defines and creates a structure ForceGPURuntimeLinking which creates an artificial dependency to functions defined in GPUJIT.c. The presence of this structure ensures that these functions are a part of the compiled object/library files including it.

[grosser]

Otherwise, this looks good.

include/polly/Support/LinkGPURuntime.h

1 ↗

(On Diff #99004)

The FOLDER tag looks surprising.

[singam-sanjay]

I've uploaded only a proof-of-concept version. @grosser @Meinersbur Need your suggestions with code style, location of the file, etc. Questions inlined.

CMakeLists.txt

209 ↗

(On Diff #99004)

This line makes available the files under tools/GPURuntime.

This is for a case when a program within the LLVM tree (opt, bugpoint) would require ForceGPURuntimeLinking.h. It isn't useful when the file is to be accessed by an external entitiy, e.g. Julia, since the line(s) that'll include <polly_src>/tools will have to be added to the compile commands of the tool.

include/polly/Support/LinkGPURuntime.h

1 ↗

(On Diff #99004)

Which folder would you recommend placing this file ? It's currently in include/polly/Support.

18 ↗

(On Diff #99004)

Although the Julia (the external tool) compiled without this construct, would it be better to enclose the #include line inside this extern "C" since it specifies that the code within should be treated as C code ?

e.g. Lines like the following, in GPUJIT.c, which are allowed in the default C dialect used by GCC, would fail when compiled as C++ ( although it didn't this time. Why was that the case ? )

• PollyGPUFunction *Function = malloc(sizeof(PollyGPUFunction)); (1 , 2)
• PollyGPUDevicePtr *DevData = malloc(sizeof(PollyGPUDevicePtr));

34 ↗

(On Diff #99004)

Should I typecast the nullptr (like in the line below) or leave it as is ?

[singam-sanjay]

1. Stylistic changes
2. Used static structure instead of func call to force link.

[singam-sanjay]

include/polly/Support/LinkGPURuntime.h

34 ↗

(On Diff #99004)

I've removed all pointer and integer type casts.

43 ↗

(On Diff #99134)

I'm now using a static structure variable instead a function call to force-link, like LinkAllIR.h. This change would make it simpler to force-link by only requiring a #include line for LinkGPURuntime.h .

[singam-sanjay]

@grosser Could you please review this patch ? Julia has accepted my PR to introduce the USE_POLLY_ACC option and uses LinkGPURuntime.h to Link GPURuntime into libjulia.so. Please leave your comments to get this patch working ASAP, before someone tries out USE_POLLY_ACC:=1.

[grosser]

Hi Sanjay,

this looks overall good. However, there is one question open:

include/polly/Support/LinkGPURuntime.h

18 ↗

(On Diff #99004)

Why are you including the full .c file? You should probably introduce a GPUJIT.h header file and only include this one. Like this there is also no need to make CUDA or OpenCL includes available when linking.

[singam-sanjay]

include/polly/Support/LinkGPURuntime.h

18 ↗

(On Diff #99004)

I did it this way having Julia in mind. If I had to #include just the GPUJIT.h, I'd have to link libGPURuntime.so to libjulia.so, which would require the rpath to libGPURuntime.so's location. But, the reviewers weren't happy with explicitly adding the rpath. So, I included GPUJIT.c and called every function to ensure an equivalent of linking to GPURuntime happend when I included LinkGPURuntime.h.

I'm now working to see if I could do away with GPUJIT.c and make libGPURuntime.so available by copying it to locations specified in RPATH of libjulia.so.

[singam-sanjay]

Not pulling in entire GPUJIT.c anymore. Has to be made available by linking to libGPURuntime.

[grosser]

This LGTM. Should I commit it?

[singam-sanjay]

In D33198#761946, @grosser wrote:

This LGTM. Should I commit it?

If you're asking me, please go ahead.

polly/trunk/include/polly/Support/LinkGPURuntime.h

+//===- Support/LinkGPURuntime.h -- Headerfile to help force-link GPURuntime  =//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This header helps pull in libGPURuntime.so
+//
+//===----------------------------------------------------------------------===//
+#ifndef POLLY_LINK_GPURUNTIME
+#define POLLY_LINK_GPURUNTIME
+
+extern "C" {
+#include "GPURuntime/GPUJIT.h"
+}
+
+namespace polly {
+struct ForceGPURuntimeLinking {
+  ForceGPURuntimeLinking() {
+    if (std::getenv("bar") != (char *)-1)
+      return;
+    // We must reference GPURuntime in such a way that compilers will not
+    // delete it all as dead code, even with whole program optimization,
+    // yet is effectively a NO-OP. As the compiler isn't smart enough
+    // to know that getenv() never returns -1, this will do the job.
+    polly_initContextCL();
+    polly_initContextCUDA();
+    polly_getKernel(nullptr, nullptr);
+    polly_freeKernel(nullptr);
+    polly_copyFromHostToDevice(nullptr, nullptr, 0);
+    polly_copyFromDeviceToHost(nullptr, nullptr, 0);
+    polly_synchronizeDevice();
+    polly_launchKernel(nullptr, 0, 0, 0, 0, 0, nullptr);
+    polly_freeDeviceMemory(nullptr);
+    polly_freeContext(nullptr);
+    polly_synchronizeDevice();
+  }
+} structure;
+} // namespace polly
+#endif