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October 6, 2019 09:03
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以下のようなコードがあるとする. | |
block.1: | |
vreg.1 = load [stack.0] | |
br block.2 if vreg.1 < 100 | |
br block.3 | |
block.2: | |
call @something | |
inc = add vreg.1, 1 | |
store inc, [stack.0] | |
br block.1 | |
block.3: | |
ret | |
ここで,call @somethingのせいでvreg.1はkillされるので, | |
call @somethingの周りでvreg.1の退避・リロードをする必要がある. | |
例えば以下の通り. | |
block.1: | |
vreg.1 = load [stack.0] | |
br block.2 if vreg.1 < 100 | |
br block.3 | |
block.2: | |
store vreg.1, [stack.1] // 退避 | |
call @something | |
vreg.2 = load [stack.1] // リロード.SSAなのでvreg.2が誕生. | |
inc = add vreg.2, 1 // vreg.1はvreg.2に置き換えられた. | |
store inc, [stack.0] | |
br block.1 | |
block.3: | |
ret | |
しかし上記のようなコードだと,block.2からblock.1へとbrするため,再びvreg.1が現れてしまう.block.2でvreg.1は死んだはずなのに. | |
どうすればいいのでしょうか. |
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