[llvm] [LangRef][IR] Fix default AS documentation for allocas without explicit AS (PR #135942)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-ir

Author: Fabian Ritter (ritter-x2a)

<details>
<summary>Changes</summary>

So far, the Language Reference said that the alloca address space from the datalayout is used if no explicit address space is provided, which is not what the LLParser and the AsmWriter implement. This patch adjusts the documentation to match the implementation: The default AS 0 is used if none is explicitly specified.

This is an alternative to PR #<!-- -->135786, which would change the parser's behavior to match the Language Reference instead.

---
Full diff: https://github.com/llvm/llvm-project/pull/135942.diff


1 Files Affected:

- (modified) llvm/docs/LangRef.rst (+6-4) 


``````````diff
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index 769003a90f959..ba2c4467703cf 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -11102,9 +11102,8 @@ 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.  If the address space is not explicitly
-specified, the object is allocated in the alloca address space from the
-:ref:`datalayout string<langref_datalayout>`.
+function returns to its caller. If the address space is not explicitly
+specified, the default address space 0 is used.
 
 Arguments:
 """"""""""
@@ -11146,7 +11145,10 @@ which way the stack grows) is not specified.
 
 Note that '``alloca``' outside of the alloca address space from the
 :ref:`datalayout string<langref_datalayout>` is meaningful only if the
-target has assigned it a semantics.
+target has assigned it a semantics. For targets that specify a non-zero alloca
+address space in the :ref:`datalayout string<langref_datalayout>`, the alloca
+address space needs to be explicitly specified in the instruction if it is to be
+used.
 
 If the returned pointer is used by :ref:`llvm.lifetime.start <int_lifestart>`,
 the returned object is initially dead.

``````````

</details>


https://github.com/llvm/llvm-project/pull/135942