LICM: add an optimization to move multiple loads and stores from/to the same memory location out of a loop. #27990
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Because the set includes all side-effect instructions, also may-reads. NFC
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…he same memory location out of a loop.
This is a combination of load hoisting and store sinking, e.g.
preheader:
br header_block
header_block:
%x = load %not_aliased_addr
// use %x and define %y
store %y to %not_aliased_addr
...
exit_block:
is transformed to:
preheader:
%x = load %not_aliased_addr
br header_block
header_block:
// use %x and define %y
...
exit_block:
store %y to %not_aliased_addr
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@swift-ci test |
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Build failed |
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Build failed |
atrick
reviewed
Nov 13, 2019
| // If a store just stores the loaded value, bail. The operand (= the load) | ||
| // will be removed later, so it cannot be used as available value. | ||
| // This corner case is suprisingly hard to handle, so we just give up. | ||
| if (isLoadFromAddr(dyn_cast<LoadInst>(SI->getSrc()), addr)) |
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I guess this isLoadFromAddr was a bug that you found after the first implementation, but I really don't get it. Just remove the store if it's not changing the available value! The SSA updater should get it right if it doesn't see this store as a def.
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This is a combination of load hoisting and store sinking, e.g.
is transformed to:
This optimization is important to optimize inout arguments, especially with COW support in SIL: it relies on values being in SSA values rather than in memory.
This is the second try to land #27849. It includes the fix which broke the ASAN bot.