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[IR] Allow alignstack attribute on return values (#130439)

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The PTX target allows an alignment to be specified on both return values
and parameters to allow for more efficient vectorized stores. Currently
we represent these parameter alignments via the "alignstack" attribute,
but must fall back to metadata for the return value. This PR allows
"alignstack" on return values as well.
This commit is contained in:
Alex MacLean
2025-03-17 14:22:08 -07:00
committed by GitHub
parent 4336e5edbc
commit 0191307bb2
3 changed files with 15 additions and 10 deletions
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12
llvm/docs/LangRef.rst
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@@ -1616,12 +1616,12 @@ Currently, only the following parameter attributes are defined:
``alignstack(<n>)``
This indicates the alignment that should be considered by the backend when
assigning this parameter to a stack slot during calling convention
lowering. The enforcement of the specified alignment is target-dependent,
as target-specific calling convention rules may override this value. This
attribute serves the purpose of carrying language specific alignment
information that is not mapped to base types in the backend (for example,
over-alignment specification through language attributes).
assigning this parameter or return value to a stack slot during calling
convention lowering. The enforcement of the specified alignment is
target-dependent, as target-specific calling convention rules may override
this value. This attribute serves the purpose of carrying language specific
alignment information that is not mapped to base types in the backend (for
example, over-alignment specification through language attributes).
``allocalign``
The function parameter marked with this attribute is the alignment in bytes of the

2
llvm/include/llvm/IR/Attributes.td
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@@ -291,7 +291,7 @@ def SExt : EnumAttr<"signext", IntersectPreserve, [ParamAttr, RetAttr]>;
/// Alignment of stack for function (3 bits) stored as log2 of alignment with
/// +1 bias 0 means unaligned (different from alignstack=(1)).
def StackAlignment : IntAttr<"alignstack", IntersectPreserve, [FnAttr, ParamAttr]>;
def StackAlignment : IntAttr<"alignstack", IntersectPreserve, [FnAttr, ParamAttr, RetAttr]>;
/// Function can be speculated.
def Speculatable : EnumAttr<"speculatable", IntersectAnd, [FnAttr]>;

11
llvm/test/CodeGen/NVPTX/param-overalign.ll
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@@ -45,7 +45,7 @@ define float @caller_md(float %a, float %b) {
ret float %r
}
define float @callee_md(%struct.float2 %a) {
define float @callee_md(%struct.float2 alignstack(8) %a) {
; CHECK-LABEL: .visible .func (.param .b32 func_retval0) callee_md(
; CHECK-NEXT: .param .align 8 .b8 callee_md_param_0[8]
; CHECK-NEXT: )
@@ -105,5 +105,10 @@ define float @callee(%struct.float2 alignstack(8) %a ) {
ret float %2
}
!nvvm.annotations = !{!0}
!0 = !{ptr @callee_md, !"align", i32 u0x00010008}
define alignstack(8) %struct.float2 @aligned_return(%struct.float2 %a ) {
; CHECK-LABEL: .visible .func (.param .align 8 .b8 func_retval0[8]) aligned_return(
; CHECK-NEXT: .param .align 4 .b8 aligned_return_param_0[8]
; CHECK-NEXT: )
; CHECK-NEXT: {
ret %struct.float2 %a
}