Remove pointer comparison from slice equality #80209
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rust-highfive
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re #71735 (comment): I'm not sure how to test |
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Can we use an older version of hyper perhaps? |
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Hmm, even circa May 2016, Using
So basically what you'd expect, reverting this makes string comparison marginally slower, but comparing the enum directly is ~the same. Although to be honest I'm not really happy with either my benchmark or what #33892 (comment) describes. Yes, they involve other code, but the only thing that changes is one critical line--basically a microbenchmark with extra steps. But I'm not sure what a good, noncontrived benchmark for this would be. |
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I think the codegen test here should probably be changed to test for something we expect to be present, rather than the lack of pointer equality - I am not sure what the IR with this PR looks like, but maybe we can assert that there is a single memcmp generated or something along those lines? I am fine with not trying to test hyper further; I still believe that the check here for pointer equality is unlikely to be impactful in practice (and we know it actively hurts some cases). @bors rollup=never though. |
Mark-Simulacrum
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Changed the test, let me know if you have a better pattern. The old IR is: define zeroext i1 @is_zero_slice([4 x i8]* noalias readonly align 1 dereferenceable(4) %data) unnamed_addr #0 {
start:
%0 = icmp eq [4 x i8]* %data, getelementptr inbounds (<{ [4 x i8] }>, <{ [4 x i8] }>* @alloc2, i64 0, i32 0)
br i1 %0, label %"_ZN4core5array103_$LT$impl$u20$core..cmp..PartialEq$LT$$u5b$B$u3b$$u20$N$u5d$$GT$$u20$for$u20$$u5b$A$u3b$$u20$N$u5d$$GT$2eq17h702fd33f1073d678E.exit", label %bb9.i.i.i
bb9.i.i.i: ; preds = %start
%1 = getelementptr [4 x i8], [4 x i8]* %data, i64 0, i64 0
%bcmp.i.i.i = tail call i32 @bcmp(i8* nonnull dereferenceable(4) %1, i8* nonnull dereferenceable(4) getelementptr inbounds (<{ [4 x i8] }>, <{ [4 x i8] }>* @alloc2, i64 0, i32 0, i64 0), i64 4) #2
%2 = icmp eq i32 %bcmp.i.i.i, 0
br label %"_ZN4core5array103_$LT$impl$u20$core..cmp..PartialEq$LT$$u5b$B$u3b$$u20$N$u5d$$GT$$u20$for$u20$$u5b$A$u3b$$u20$N$u5d$$GT$2eq17h702fd33f1073d678E.exit"
"_ZN4core5array103_$LT$impl$u20$core..cmp..PartialEq$LT$$u5b$B$u3b$$u20$N$u5d$$GT$$u20$for$u20$$u5b$A$u3b$$u20$N$u5d$$GT$2eq17h702fd33f1073d678E.exit": ; preds = %start, %bb9.i.i.i
%.0.i.i.i = phi i1 [ %2, %bb9.i.i.i ], [ true, %start ]
ret i1 %.0.i.i.i
}and the new IR is: define zeroext i1 @is_zero_slice([4 x i8]* noalias nocapture readonly align 1 dereferenceable(4) %data) unnamed_addr #0 {
start:
%0 = getelementptr [4 x i8], [4 x i8]* %data, i64 0, i64 0
%bcmp.i.i.i = tail call i32 @bcmp(i8* nonnull dereferenceable(4) %0, i8* nonnull dereferenceable(4) getelementptr inbounds (<{ [4 x i8] }>, <{ [4 x i8] }>* @alloc2, i64 0, i32 0, i64 0), i64 4) #2
%1 = icmp eq i32 %bcmp.i.i.i, 0
ret i1 %1
} |
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Yeah, I think the test is good. We can relax it if it turns out to be too sensitive. @bors r+ rollup=never squash |
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📌 Commit f29b6b8 has been approved by |
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⌛ Testing commit f29b6b8 with merge 280255c7b4b67d559361bdd77d0f1f9c22b073b2... |
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The job Click to see the possible cause of the failure (guessed by this bot) |
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💔 Test failed - checks-actions |
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@bors r+ squash rollup=never |
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📌 Commit fae3ede has been approved by |
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⌛ Testing commit fae3ede with merge 93bac3bc6043448eb0b1de155765fbe6318656ec... |
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The job Click to see the possible cause of the failure (guessed by this bot) |
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💔 Test failed - checks-actions |
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@bors retry |
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⌛ Testing commit fae3ede with merge 80cb6a64ae252b9aa8682fecabd621506106a115... |
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The job Click to see the possible cause of the failure (guessed by this bot) |
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💔 Test failed - checks-actions |
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looks like another spurious failure |
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@bors retry |
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Dec 26, 2020
Remove pointer comparison from slice equality This resurrects rust-lang#71735. Fixes rust-lang#71602, helps with rust-lang#80140. r? `@Mark-Simulacrum`
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☀️ Test successful - checks-actions |
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Why was the PR not auto-closed? Is this a github bug or bors bug? |
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It also removes authorship (733cb54), which is unusual; I would expect the resulting commit from this rebase command to have the same author as the first commit from the PR. |
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Yeah, those both seem like bors bugs. I will try to investigate later today. |
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This resurrects #71735.
Fixes #71602, helps with #80140.
r? @Mark-Simulacrum