[CIR] Lower nested local constant alloca #1261
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This patch adds support for lowering local constants in nested scopes, including those in nested loops. For those constant allocas in non-loop inner scopes, this patch keeps their constant flags during alloca hoisting. LLVM lowering would correctly emit necessary invariant metadata for those allocas. For those constant allocas in a loop, this patch introduces a new operation `cir.invariant_group` that marks the beginning of the lifetime of the constant objects. This operation is put at the location of the alloca operation before hoisting them. This patch updates LLVM lowering to emit the necessary invariant metadata when loading and storing through such pointers. This patch takes care of the special case where the constant alloca represents a variable declared in the condition part of a while loop. In such a case, this patch removes the constant flag on the alloca operation when hositing them.
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This PR adds support for lowering local constants in nested scopes, including those in nested loops.
For those constant allocas in non-loop inner scopes, this PR keeps their constant flags during alloca hoisting. LLVM lowering would correctly emit necessary invariant metadata for those allocas.
For those constant allocas in a loop, this PR introduces a new operation
cir.invariant_groupthat marks the beginning of the lifetime of the constant objects. This operation is put at the location of the alloca operation before hoisting them. This PR updates LLVM lowering to emit the necessary invariant metadata when loading and storing through such pointers.This PR takes care of the special case where the constant alloca represents a variable declared in the condition part of a while loop. In such a case, this PR removes the constant flag on the alloca operation when hositing them.