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Diffstat (limited to 'llvm/docs/LangRef.rst')
| -rw-r--r-- | llvm/docs/LangRef.rst | 74 |
1 files changed, 41 insertions, 33 deletions
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst index ddbf4003494..891b9c0af70 100644 --- a/llvm/docs/LangRef.rst +++ b/llvm/docs/LangRef.rst @@ -2837,50 +2837,58 @@ noalias memory-access sets. This means that some collection of memory access instructions (loads, stores, memory-accessing calls, etc.) that carry ``noalias`` metadata can specifically be specified not to alias with some other collection of memory access instructions that carry ``alias.scope`` metadata. -Each type of metadata specifies a list of scopes, and when evaluating an -aliasing query, if one of the instructions has a scope in its ``alias.scope`` -list that is identical to a scope in the other instruction's ``noalias`` list, -or is a descendant (in the scope hierarchy) of a scope in the other -instruction's ``noalias`` list , then the two memory accesses are assumed not -to alias. - -The metadata identifying each scope is itself a list containing one or two -entries. The first entry is the name of the scope. Note that if the name is a +Each type of metadata specifies a list of scopes where each scope has an id and +a domain. When evaluating an aliasing query, if for some some domain, the set +of scopes with that domain in one instruction's ``alias.scope`` list is a +subset of (or qual to) the set of scopes for that domain in another +instruction's ``noalias`` list, then the two memory accesses are assumed not to +alias. + +The metadata identifying each domain is itself a list containing one or two +entries. The first entry is the name of the domain. Note that if the name is a string then it can be combined accross functions and translation units. A -self-reference can be used to create globally unique scope names. -Optionally, a metadata reference to a parent scope can be provided as a second -entry in the list. +self-reference can be used to create globally unique domain names. A +descriptive string may optionally be provided as a second list entry. + +The metadata identifying each scope is also itself a list containing two or +three entries. The first entry is the name of the scope. Note that if the name +is a string then it can be combined accross functions and translation units. A +self-reference can be used to create globally unique scope names. A metadata +reference to the scope's domain is the second entry. A descriptive string may +optionally be provided as a third list entry. For example, .. code-block:: llvm - ; A root scope (which doubles as a list of itself): + ; Two scope domains: !0 = metadata !{metadata !0} + !1 = metadata !{metadata !1} - ; Two child scopes (which must be self-referential to avoid being "uniqued"): - !1 = metadata !{metadata !2} ; A list containing only scope !2 - !2 = metadata !{metadata !2, metadata !0} ; Scope !2 is a descendant of scope !0 + ; Some scopes in these domains: + !2 = metadata !{metadata !2, metadata !0} + !3 = metadata !{metadata !3, metadata !0} + !4 = metadata !{metadata !4, metadata !1} - !3 = metadata !{metadata !4} ; A list containing only scope !4 - !4 = metadata !{metadata !4, metadata !0} ; Scope !4 is a descendant of scope !0 + ; Some scope lists: + !5 = metadata !{metadata !4} ; A list containing only scope !4 + !6 = metadata !{metadata !4, metadata !3, metadata !2} + !7 = metadata !{metadata !3} ; These two instructions don't alias: - %0 = load float* %c, align 4, !alias.scope !0 - store float %0, float* %arrayidx.i, align 4, !noalias !0 - - ; These two instructions may alias (scope !2 and scope !4 are peers): - %2 = load float* %c, align 4, !alias.scope !1 - store float %2, float* %arrayidx.i2, align 4, !noalias !3 - - ; These two instructions don't alias (scope !2 is a descendant of scope !0 - ; and the store does not alias with anything in scope !0 or any of its descendants): - %2 = load float* %c, align 4, !alias.scope !1 - store float %0, float* %arrayidx.i, align 4, !noalias !0 - - ; These two instructions may alias: - %2 = load float* %c, align 4, !alias.scope !0 - store float %0, float* %arrayidx.i, align 4, !noalias !1 + %0 = load float* %c, align 4, !alias.scope !5 + store float %0, float* %arrayidx.i, align 4, !noalias !5 + + ; These two instructions also don't alias (for domain !1, the set of scopes + ; in the !alias.scope equals that in the !noalias list): + %2 = load float* %c, align 4, !alias.scope !5 + store float %2, float* %arrayidx.i2, align 4, !noalias !6 + + ; These two instructions don't alias (for domain !0, the set of scopes in + ; the !noalias list is not a superset of, or equal to, the scopes in the + ; !alias.scope list): + %2 = load float* %c, align 4, !alias.scope !6 + store float %0, float* %arrayidx.i, align 4, !noalias !7 '``fpmath``' Metadata ^^^^^^^^^^^^^^^^^^^^^ |
