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Reapply r281276 with passing -emit-llvm in one of the tests Original commit message: Add -fdiagnostics-show-hotness Summary: I've recently added the ability for optimization remarks to include the hotness of the corresponding code region. This uses PGO and allows filtering of the optimization remarks by relevance. The idea was first discussed here: http://thread.gmane.org/gmane.comp.compilers.llvm.devel/98334 The general goal is to produce a YAML file with the remarks. Then, an external tool could dynamically filter these by hotness and perhaps by other things. That said it makes sense to also expose this at the more basic level where we just include the hotness info with each optimization remark. For example, in D22694, the clang flag was pretty useful to measure the overhead of the additional analyses required to include hotness. (Without the flag we don't even run the analyses.) For the record, Hal has already expressed support for the idea of this patch on IRC. Differential Revision: https://reviews.llvm.org/D23284 llvm-svn: 281293
2016-09-13 12:32:40 +08:00
foo
# Func Hash:
[PGO] Detect more structural changes with the stable hash Lifting from Bob Wilson's notes: The hash value that we compute and store in PGO profile data to detect out-of-date profiles does not include enough information. This means that many significant changes to the source will not cause compiler warnings about the profile being out of date, and worse, we may continue to use the outdated profile data to make bad optimization decisions. There is some tension here because some source changes won't affect PGO and we don't want to invalidate the profile unnecessarily. This patch adds a new hashing scheme which is more sensitive to loop nesting, conditions, and out-of-order control flow. Here are examples which show snippets which get the same hash under the current scheme, and different hashes under the new scheme: Loop Nesting Example -------------------- // Snippet 1 while (foo()) { while (bar()) {} } // Snippet 2 while (foo()) {} while (bar()) {} Condition Example ----------------- // Snippet 1 if (foo()) bar(); baz(); // Snippet 2 if (foo()) bar(); else baz(); Out-of-order Control Flow Example --------------------------------- // Snippet 1 while (foo()) { if (bar()) {} baz(); } // Snippet 2 while (foo()) { if (bar()) continue; baz(); } In each of these cases, it's useful to differentiate between the snippets because swapping their profiles gives bad optimization hints. The new hashing scheme considers some logical operators in an effort to detect more changes in conditions. This isn't a perfect scheme. E.g, it does not produce the same hash for these equivalent snippets: // Snippet 1 bool c = !a || b; if (d && e) {} // Snippet 2 bool f = d && e; bool c = !a || b; if (f) {} This would require an expensive data flow analysis. Short of that, the new hashing scheme looks reasonably complete, based on a scan over the statements we place counters on. Profiles which use the old version of the PGO hash remain valid and can be used without issue (there are tests in tree which check this). rdar://17068282 Differential Revision: https://reviews.llvm.org/D39446 llvm-svn: 318229
2017-11-15 07:56:53 +08:00
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Reapply r281276 with passing -emit-llvm in one of the tests Original commit message: Add -fdiagnostics-show-hotness Summary: I've recently added the ability for optimization remarks to include the hotness of the corresponding code region. This uses PGO and allows filtering of the optimization remarks by relevance. The idea was first discussed here: http://thread.gmane.org/gmane.comp.compilers.llvm.devel/98334 The general goal is to produce a YAML file with the remarks. Then, an external tool could dynamically filter these by hotness and perhaps by other things. That said it makes sense to also expose this at the more basic level where we just include the hotness info with each optimization remark. For example, in D22694, the clang flag was pretty useful to measure the overhead of the additional analyses required to include hotness. (Without the flag we don't even run the analyses.) For the record, Hal has already expressed support for the idea of this patch on IRC. Differential Revision: https://reviews.llvm.org/D23284 llvm-svn: 281293
2016-09-13 12:32:40 +08:00
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bar
# Func Hash:
0
# Num Counters:
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main
# Func Hash:
[PGO] Detect more structural changes with the stable hash Lifting from Bob Wilson's notes: The hash value that we compute and store in PGO profile data to detect out-of-date profiles does not include enough information. This means that many significant changes to the source will not cause compiler warnings about the profile being out of date, and worse, we may continue to use the outdated profile data to make bad optimization decisions. There is some tension here because some source changes won't affect PGO and we don't want to invalidate the profile unnecessarily. This patch adds a new hashing scheme which is more sensitive to loop nesting, conditions, and out-of-order control flow. Here are examples which show snippets which get the same hash under the current scheme, and different hashes under the new scheme: Loop Nesting Example -------------------- // Snippet 1 while (foo()) { while (bar()) {} } // Snippet 2 while (foo()) {} while (bar()) {} Condition Example ----------------- // Snippet 1 if (foo()) bar(); baz(); // Snippet 2 if (foo()) bar(); else baz(); Out-of-order Control Flow Example --------------------------------- // Snippet 1 while (foo()) { if (bar()) {} baz(); } // Snippet 2 while (foo()) { if (bar()) continue; baz(); } In each of these cases, it's useful to differentiate between the snippets because swapping their profiles gives bad optimization hints. The new hashing scheme considers some logical operators in an effort to detect more changes in conditions. This isn't a perfect scheme. E.g, it does not produce the same hash for these equivalent snippets: // Snippet 1 bool c = !a || b; if (d && e) {} // Snippet 2 bool f = d && e; bool c = !a || b; if (f) {} This would require an expensive data flow analysis. Short of that, the new hashing scheme looks reasonably complete, based on a scan over the statements we place counters on. Profiles which use the old version of the PGO hash remain valid and can be used without issue (there are tests in tree which check this). rdar://17068282 Differential Revision: https://reviews.llvm.org/D39446 llvm-svn: 318229
2017-11-15 07:56:53 +08:00
1160280
Reapply r281276 with passing -emit-llvm in one of the tests Original commit message: Add -fdiagnostics-show-hotness Summary: I've recently added the ability for optimization remarks to include the hotness of the corresponding code region. This uses PGO and allows filtering of the optimization remarks by relevance. The idea was first discussed here: http://thread.gmane.org/gmane.comp.compilers.llvm.devel/98334 The general goal is to produce a YAML file with the remarks. Then, an external tool could dynamically filter these by hotness and perhaps by other things. That said it makes sense to also expose this at the more basic level where we just include the hotness info with each optimization remark. For example, in D22694, the clang flag was pretty useful to measure the overhead of the additional analyses required to include hotness. (Without the flag we don't even run the analyses.) For the record, Hal has already expressed support for the idea of this patch on IRC. Differential Revision: https://reviews.llvm.org/D23284 llvm-svn: 281293
2016-09-13 12:32:40 +08:00
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