Turn new address space rules by default #242
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Static variables without address space now reside in global address space, unless they have an explicit address space qualifier in source code. Signed-off-by: Andrew Savonichev <[email protected]>
We cannot return a generic pointer like in 'global', 'local' and 'private' cases, because 'constant' and 'generic' address spaces do not overlap. This patch returns __constant pointer as is, and assumes that a user have to deal with __constant pointer limitations (ie. such pointers cannot be casted to plain (default) pointers). Signed-off-by: Andrew Savonichev <[email protected]>
This patch enables new rules for address space handling in SYCL by
default. Previous rules for address space handling can still be
enabled by DISABLE_INFER_AS=1 environment variable.
This approach is known as "generic pointers by default", and
it essentially makes all pointers without an explicit address space
qualifier to be pointers in generic address space.
For example:
void foo() {
int* ip = foo();
}
void* bar(int* ip);
template <typename T>
void swap(T&, T&) {}
All pointers (and references) in the example above are CodeGen'ed as
pointers in addrspace(4) in LLVM IR (where '4' is a number for generic
address space).
Concrete address space (global, local and private) can originate from:
1) an address-of operation applied to an automatic variable:
int i = 42;
(void) &i // <--- this is a private pointer
2) Static variable
3) SYCL global, local, or constant buffers
In all three cases, once this pointer is used, it is immediately
addrspacecast'ed to generic, because a user does not (and should not)
specify address space for pointers in source code.
Signed-off-by: Andrew Savonichev <[email protected]>
Although OpenCL specification explicitly states that a string literal
should reside in constant address space, it does not work for SYCL
with "generic by default" address space rules.
For example:
const char *getLiteral() {
return "A";
}
void func(bool AorB) {
char B[] = {'B', '\0'};
const char* C = AorB ? A : B;
}
If `A' reside in constant address space, it cannot be returned from a
function `getLiteral', because it returns a generic const char*.
Signed-off-by: Andrew Savonichev <[email protected]>
Could this be implemented via a command-line flag instead of an environmental variable? |
I considered making an option for this, but it takes more effort to pass a flag to all places this patch changes, and it doesn't seem to worth it. |
| @@ -63,7 +63,7 @@ class LLVM_LIBRARY_VISIBILITY SPIRTargetInfo : public TargetInfo { | |||
| VLASupported = false; | |||
| LongWidth = LongAlign = 64; | |||
| if (Triple.getEnvironment() == llvm::Triple::SYCLDevice && | |||
| getenv("ENABLE_INFER_AS")) { | |||
| !getenv("DISABLE_INFER_AS")) { | |||
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Even if it is a temporary solution, naming the environment variable such as SYCL_CLANG_DISABLE_INFER_AS or whatever so we can understand among the crowded output of a printenv.
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I'll change the variable name in a follow-up commit.
| @@ -1063,6 +1063,8 @@ static void InitializePredefinedMacros(const TargetInfo &TI, | |||
| // SYCL device compiler which doesn't produce host binary. | |||
| if (LangOpts.SYCLIsDevice) { | |||
| Builder.defineMacro("__SYCL_DEVICE_ONLY__", "1"); | |||
| if (!getenv("DISABLE_INFER_AS")) | |||
| Builder.defineMacro("__SYCL_ENABLE_INFER_AS__", "1"); | |||
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Probably this name should serve as a starting point for the environment variable.
InferAddressSpaces can be used to cleanup generic address space pointers in the optimization phase. It generally performs pretty good on an optimized IR (after mem2reg and inlining is done).
If a device does not support OpenCL 2.0 Generic address space feature, then such device can be used only if you run InferAddressSpaces pass (or a similar pass) before passing code to the device compiler. In some cases, generic address space pointers cannot be resolved statically, and this approach will not work. OpenCL 2.0 (or 1.x + GAS feature) devices should work fine with any SYCL code. |
| // const char *getLiteral() n{ | ||
| // return "AB"; | ||
| // } | ||
| return LangAS::opencl_private; |
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// If we keep a literal string in constant address space, the following code
// becomes illegal:
Why not global then?
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This is a good question - I don't know what is the best address space for this.
I used private address space mainly because it was used to lower a string literal before I changed address spaces by this patch.
CONFLICT (modify/delete): clang/test/CodeGenSYCL/unique-stable-name.cpp deleted in cec49a5 and modified in HEAD. Version HEAD of clang/test/CodeGenSYCL/unique-stable-name.cpp left in tree.
This patch enables new rules for address space handling in SYCL by
default. Previous rules for address space handling can still be
enabled by DISABLE_INFER_AS=1 environment variable.
This approach is known as "generic pointers by default", and
it essentially makes all pointers without an explicit address space
qualifier to be pointers in generic address space.
For example:
All pointers (and references) in the example above are CodeGen'ed as
pointers in addrspace(4) in LLVM IR (where '4' is a number for generic
address space).
Concrete address space (global, local and private) can originate from:
Static variable
SYCL global, local, or constant buffers
In all three cases, once this pointer is used, it is immediately
addrspacecast'ed to generic, because a user does not (and should not)
specify address space for pointers in source code.