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| author | Matt Arsenault <Matthew.Arsenault@amd.com> | 2017-04-10 22:27:50 +0000 |
|---|---|---|
| committer | Matt Arsenault <Matthew.Arsenault@amd.com> | 2017-04-10 22:27:50 +0000 |
| commit | 3c1fc768ed6cf2b01463df036ae6ae3b1f0de632 (patch) | |
| tree | 7893b430cd0be51c8e7e2db97e49415820615c83 /llvm/docs | |
| parent | d78bd57b3f24ba97c2b0112d2cf6b5a6896fd67d (diff) | |
| download | bcm5719-llvm-3c1fc768ed6cf2b01463df036ae6ae3b1f0de632.tar.gz bcm5719-llvm-3c1fc768ed6cf2b01463df036ae6ae3b1f0de632.zip | |
Allow DataLayout to specify addrspace for allocas.
LLVM makes several assumptions about address space 0. However,
alloca is presently constrained to always return this address space.
There's no real way to avoid using alloca, so without this
there is no way to opt out of these assumptions.
The problematic assumptions include:
- That the pointer size used for the stack is the same size as
the code size pointer, which is also the maximum sized pointer.
- That 0 is an invalid, non-dereferencable pointer value.
These are problems for AMDGPU because alloca is used to
implement the private address space, which uses a 32-bit
index as the pointer value. Other pointers are 64-bit
and behave more like LLVM's notion of generic address
space. By changing the address space used for allocas,
we can change our generic pointer type to be LLVM's generic
pointer type which does have similar properties.
llvm-svn: 299888
Diffstat (limited to 'llvm/docs')
| -rw-r--r-- | llvm/docs/LangRef.rst | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst index 53be12ca709..e68b1a80152 100644 --- a/llvm/docs/LangRef.rst +++ b/llvm/docs/LangRef.rst @@ -1812,6 +1812,9 @@ as follows: must be a multiple of 8-bits. If omitted, the natural stack alignment defaults to "unspecified", which does not prevent any alignment promotions. +``A<address space>`` + Specifies the address space of objects created by '``alloca``'. + Defaults to the default address space of 0. ``p[n]:<size>:<abi>:<pref>`` This specifies the *size* of a pointer and its ``<abi>`` and ``<pref>``\erred alignments for address space ``n``. All sizes are in @@ -7192,7 +7195,7 @@ Syntax: :: - <result> = alloca [inalloca] <type> [, <ty> <NumElements>] [, align <alignment>] ; yields type*:result + <result> = alloca [inalloca] <type> [, <ty> <NumElements>] [, align <alignment>] [, addrspace(<num>)] ; yields type addrspace(num)*:result Overview: """"""""" @@ -7200,7 +7203,7 @@ Overview: The '``alloca``' instruction allocates memory on the stack frame of the currently executing function, to be automatically released when this function returns to its caller. The object is always allocated in the -default address space (address space zero). +address space for allocas indicated in the datalayout. Arguments: """""""""" |
