ICU-23253 Add Link Time Optimization to release flags #3765

grhoten · 2025-11-05T06:13:32Z

The runConfigureICU script should add Link Time Optimization (-flto) to the release flags for ongoing testing on macOS. It can provide substantial performance improvements.

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Required: Issue filed: ICU-23253
Required: The PR title must be prefixed with a JIRA Issue number. Example: "ICU-NNNNN Fix xyz"
Required: Each commit message must be prefixed with a JIRA Issue number. Example: "ICU-NNNNN Fix xyz"
Issue accepted (done by Technical Committee after discussion)
Tests included, if applicable
API docs and/or User Guide docs changed or added, if applicable
Approver: Feel free to merge on my behalf

jira-pull-request-webhook · 2025-11-07T06:42:14Z

Hooray! The files in the branch are the same across the force-push. 😃

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grhoten · 2025-11-07T06:50:27Z

FYI the following warnings appeared when I used Linux/gcc. Most of the warnings appeared at link time.

lto-wrapper: warning: using serial compilation of 23 LTRANS jobs
In member function ‘length’,
    inlined from ‘setTo’ at ../../common/unicode/unistr.h:5015:17,
    inlined from ‘u_getFC_NFKC_Closure_79’ at ../../common/uprops.cpp:1019:28:
../../common/unicode/unistr.h:4274:27: warning: ‘folded1String.fUnion.fFields.fLength’ may be used uninitialized [-Wmaybe-uninitialized]
 4274 |   return hasShortLength() ? getShortLength() : fUnion.fFields.fLength;
      |                           ^
../../common/uprops.cpp: In function ‘u_getFC_NFKC_Closure_79’:
../../common/uprops.cpp:1011:19: note: ‘folded1String’ declared here
 1011 |     UnicodeString folded1String;
      |                   ^
In member function ‘length’,
    inlined from ‘setTo’ at ../../common/unicode/unistr.h:5015:17,
    inlined from ‘u_getFC_NFKC_Closure_79’ at ../../common/uprops.cpp:1022:32:
../../common/unicode/unistr.h:4274:27: warning: ‘folded1String.fUnion.fFields.fLength’ may be used uninitialized [-Wmaybe-uninitialized]
 4274 |   return hasShortLength() ? getShortLength() : fUnion.fFields.fLength;
      |                           ^
../../common/uprops.cpp: In function ‘u_getFC_NFKC_Closure_79’:
../../common/uprops.cpp:1011:19: note: ‘folded1String’ declared here
 1011 |     UnicodeString folded1String;
      |                   ^
../../i18n/astro.cpp: In static member function ‘static icu_79::CalendarAstronomer::MoonAge icu_79::CalendarAstronomer::NEW_MOON()’:
../../i18n/astro.cpp:653:58: note: parameter passing for argument of type ‘icu_79::CalendarAstronomer::MoonAge’ when C++17 is enabled changed to match C++14 in GCC 10.1
  653 | CalendarAstronomer::MoonAge CalendarAstronomer::NEW_MOON() {
      |                                                          ^
../../i18n/chnsecal.cpp: In function ‘int32_t icu_79::{anonymous}::newMoonNear(const icu_79::TimeZone*, double, UBool, UErrorCode&)’:
../../i18n/chnsecal.cpp:661:56: note: parameter passing for argument of type ‘icu_79::CalendarAstronomer::MoonAge’ when C++17 is enabled changed to match C++14 in GCC 10.1
  661 |               .getMoonTime(CalendarAstronomer::NEW_MOON(), after),
      |                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
lto-wrapper: warning: using serial compilation of 42 LTRANS jobs
In function ‘NEW_MOON’:
lto1: note: parameter passing for argument of type ‘struct MoonAge’ when C++17 is enabled changed to match C++14 in GCC 10.1
../../i18n/chnsecal.cpp: In function ‘newMoonNear’:
../../i18n/chnsecal.cpp:650:9: note: parameter passing for argument of type ‘struct MoonAge’ when C++17 is enabled changed to match C++14 in GCC 10.1
  650 | int32_t newMoonNear(const TimeZone* timeZone, double days, UBool after, UErrorCode& status) {
      |         ^
../../i18n/decNumber.cpp: In function ‘uprv_decNumberLog10_79’:
../../i18n/decNumber.cpp:1528:14: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1528 |     w->lsu[1]=1; w->lsu[0]=0;           /* ..  */
      |              ^
../../i18n/decNumber.h:89:19: note: at offset 1 into destination object ‘lsu’ of size 1
   89 |     decNumberUnit lsu[DECNUMUNITS];
      |                   ^
../../i18n/decNumber.cpp:1528:14: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1528 |     w->lsu[1]=1; w->lsu[0]=0;           /* ..  */
      |              ^
../../i18n/decNumber.h:89:19: note: at offset 1 into destination object ‘lsu’ of size 1
   89 |     decNumberUnit lsu[DECNUMUNITS];
      |                   ^
../../i18n/decNumber.cpp: In function ‘uprv_decNumberSquareRoot_79’:
../../i18n/decNumber.cpp:2974:31: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 2974 |         t->lsu[0]=9; t->lsu[1]=5; t->lsu[2]=2;
      |                               ^
../../i18n/decNumber.h:89:19: note: at offset 1 into destination object ‘lsu’ of size 1
   89 |     decNumberUnit lsu[DECNUMUNITS];
      |                   ^
../../i18n/decNumber.cpp:2974:44: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 2974 |         t->lsu[0]=9; t->lsu[1]=5; t->lsu[2]=2;
      |                                            ^
../../i18n/decNumber.h:89:19: note: at offset 2 into destination object ‘lsu’ of size 1
   89 |     decNumberUnit lsu[DECNUMUNITS];
      |                   ^
../../i18n/formattedvalue.cpp: In function ‘ufmtval_getString_79’:
lto1: warning: function may return address of local variable [-Wreturn-local-addr]
../../i18n/formattedvalue.cpp:210:19: note: declared here
  210 |     UnicodeString readOnlyAlias = impl->fFormattedValue->toTempString(*ec);
      |                   ^
../../i18n/number_mapper.cpp: In function ‘oldToNew’:
../../i18n/number_mapper.cpp:151:49: warning: ‘currencyUsage’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  151 |         precision = Precision::constructCurrency(currencyUsage);
      |                                                 ^
../../i18n/number_mapper.cpp:78:20: note: ‘currencyUsage’ was declared here
   78 |     UCurrencyUsage currencyUsage;
      |                    ^
In member function ‘handleReplaceBetween’,
    inlined from ‘handleTransliterate’ at ../../i18n/remtrans.cpp:64:30:
../../i18n/utrans.cpp:115:21: warning: ‘empty’ may be used uninitialized [-Wmaybe-uninitialized]
  115 |     (*func->replace)(rep, start, limit, text.getBuffer(), text.length());
      |                     ^
../../i18n/remtrans.cpp: In member function ‘handleTransliterate’:
../../i18n/utrans.cpp:115:21: note: by argument 4 of type ‘const UChar *’ to ‘void <Tf88> (void * *, int32_t, int32_t, const UChar *, int32_t)’
../../i18n/remtrans.cpp:63:19: note: ‘empty’ declared here
   63 |     UnicodeString empty;
      |                   ^
lto-wrapper: warning: using serial compilation of 2 LTRANS jobs
../../../tools/genrb/parse.cpp: In function ‘parseIntVector’:
../../../tools/genrb/parse.cpp:1775:9: warning: ‘stringLength’ may be used uninitialized in this function [-Wmaybe-uninitialized]
 1775 |         if(len==stringLength)
      |         ^
../../../tools/genrb/parse.cpp:1762:17: note: ‘stringLength’ was declared here
 1762 |         int32_t stringLength;
      |                 ^
lto-wrapper: warning: using serial compilation of 128 LTRANS jobs
In function ‘itoa’,
    inlined from ‘TestIteration’ at ../../../test/intltest/restsnew.cpp:404:39:
../../../test/intltest/restest.cpp:108:16: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  108 |         *buf++ = *p;
      |                ^
../../../test/intltest/restest.cpp:108:16: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
In function ‘itoa’,
    inlined from ‘TestIteration’ at ../../../test/intltest/restsnew.cpp:412:51:
../../../test/intltest/restest.cpp:108:16: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  108 |         *buf++ = *p;
      |                ^
../../../test/intltest/restest.cpp:108:16: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
In function ‘itoa’,
    inlined from ‘TestIteration’ at ../../../test/intltest/restsnew.cpp:413:51:
../../../test/intltest/restest.cpp:108:16: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  108 |         *buf++ = *p;
      |                ^
../../../test/intltest/restest.cpp:108:16: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
In function ‘itoa’,
    inlined from ‘TestOtherAPI’ at ../../../test/intltest/restsnew.cpp:618:43:
../../../test/intltest/restest.cpp:108:16: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  108 |         *buf++ = *p;
      |                ^
../../../test/intltest/restest.cpp:108:16: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
In function ‘itoa’,
    inlined from ‘TestOtherAPI’ at ../../../test/intltest/restsnew.cpp:629:55:
../../../test/intltest/restest.cpp:108:16: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  108 |         *buf++ = *p;
      |                ^
../../../test/intltest/restest.cpp:108:16: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
In function ‘itoa’,
    inlined from ‘TestOtherAPI’ at ../../../test/intltest/restsnew.cpp:630:55:
../../../test/intltest/restest.cpp:108:16: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  108 |         *buf++ = *p;
      |                ^
../../../test/intltest/restest.cpp:108:16: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
lto-wrapper: warning: using serial compilation of 23 LTRANS jobs
In function ‘itoa1’,
    inlined from ‘testTag.isra’ at ../../../test/cintltst/creststn.c:1814:37:
../../../test/cintltst/creststn.c:114:12: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  114 |     *buf++ = *p;
      |            ^
../../../test/cintltst/creststn.c:114:12: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
In function ‘itoa1’,
    inlined from ‘testTag.isra’ at ../../../test/cintltst/creststn.c:1853:41:
../../../test/cintltst/creststn.c:114:12: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  114 |     *buf++ = *p;
      |            ^
../../../test/cintltst/creststn.c:114:12: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
In function ‘itoa1’,
    inlined from ‘testTag.isra’ at ../../../test/cintltst/creststn.c:1904:45:
../../../test/cintltst/creststn.c:114:12: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  114 |     *buf++ = *p;
      |            ^
../../../test/cintltst/creststn.c:114:12: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
In function ‘itoa1’,
    inlined from ‘testTag.isra’ at ../../../test/cintltst/creststn.c:1953:37:
../../../test/cintltst/creststn.c:114:12: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  114 |     *buf++ = *p;
      |            ^
../../../test/cintltst/creststn.c:114:12: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
In function ‘itoa1’,
    inlined from ‘testTag.isra’ at ../../../test/cintltst/creststn.c:1955:37:
../../../test/cintltst/creststn.c:114:12: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  114 |     *buf++ = *p;
      |            ^
../../../test/cintltst/creststn.c:114:12: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
In function ‘itoa1’,
    inlined from ‘testTag.isra’ at ../../../test/cintltst/creststn.c:2013:30:
../../../test/cintltst/creststn.c:114:12: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  114 |     *buf++ = *p;
      |            ^
../../../test/cintltst/creststn.c:114:12: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
In function ‘itoa1’,
    inlined from ‘testTag.isra’ at ../../../test/cintltst/creststn.c:2039:45:
../../../test/cintltst/creststn.c:114:12: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  114 |     *buf++ = *p;
      |            ^
../../../test/cintltst/creststn.c:114:12: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]

grhoten · 2025-11-08T17:07:30Z

@markusicu Do you want to approve this as is, or do you want me to address these new gcc warnings in this pull request too? After a quick look, all of the warnings seem fixable.

grhoten · 2025-11-09T07:10:56Z

Some of the warnings seemed legitimate. I fixed what I could easily fix. The rest require deeper analysis. Here's what's left.

In member function ‘length’,
    inlined from ‘setTo’ at ../../common/unicode/unistr.h:5015:17,
    inlined from ‘u_getFC_NFKC_Closure_79’ at ../../common/uprops.cpp:1019:28:
../../common/unicode/unistr.h:4274:27: warning: ‘folded1String.fUnion.fFields.fLength’ may be used uninitialized [-Wmaybe-uninitialized]
 4274 |   return hasShortLength() ? getShortLength() : fUnion.fFields.fLength;
      |                           ^
../../common/uprops.cpp: In function ‘u_getFC_NFKC_Closure_79’:
../../common/uprops.cpp:1011:19: note: ‘folded1String’ declared here
 1011 |     UnicodeString folded1String;
      |                   ^
In member function ‘length’,
    inlined from ‘setTo’ at ../../common/unicode/unistr.h:5015:17,
    inlined from ‘u_getFC_NFKC_Closure_79’ at ../../common/uprops.cpp:1022:32:
../../common/unicode/unistr.h:4274:27: warning: ‘folded1String.fUnion.fFields.fLength’ may be used uninitialized [-Wmaybe-uninitialized]
 4274 |   return hasShortLength() ? getShortLength() : fUnion.fFields.fLength;
      |                           ^
../../common/uprops.cpp: In function ‘u_getFC_NFKC_Closure_79’:
../../common/uprops.cpp:1011:19: note: ‘folded1String’ declared here
 1011 |     UnicodeString folded1String;
      |                   ^
../../i18n/formattedvalue.cpp: In function ‘ufmtval_getString_79’:
lto1: warning: function may return address of local variable [-Wreturn-local-addr]
../../i18n/formattedvalue.cpp:210:19: note: declared here
  210 |     UnicodeString readOnlyAlias = impl->fFormattedValue->toTempString(*ec);
      |                   ^
In member function ‘handleReplaceBetween’,
    inlined from ‘handleTransliterate’ at ../../i18n/remtrans.cpp:64:30:
../../i18n/utrans.cpp:115:21: warning: ‘empty’ may be used uninitialized [-Wmaybe-uninitialized]
  115 |     (*func->replace)(rep, start, limit, text.getBuffer(), text.length());
      |                     ^
../../i18n/remtrans.cpp: In member function ‘handleTransliterate’:
../../i18n/utrans.cpp:115:21: note: by argument 4 of type ‘const UChar *’ to ‘void <Tf88> (void * *, int32_t, int32_t, const UChar *, int32_t)’
../../i18n/remtrans.cpp:63:19: note: ‘empty’ declared here
   63 |     UnicodeString empty;
      |                   ^
../../i18n/decNumber.cpp: In function ‘uprv_decNumberLog10_79’:
../../i18n/decNumber.cpp:1528:14: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1528 |     w->lsu[1]=1; w->lsu[0]=0;           /* ..  */
      |              ^
../../i18n/decNumber.h:89:19: note: at offset 1 into destination object ‘lsu’ of size 1
   89 |     decNumberUnit lsu[DECNUMUNITS];
      |                   ^
../../i18n/decNumber.cpp:1528:14: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1528 |     w->lsu[1]=1; w->lsu[0]=0;           /* ..  */
      |              ^
../../i18n/decNumber.h:89:19: note: at offset 1 into destination object ‘lsu’ of size 1
   89 |     decNumberUnit lsu[DECNUMUNITS];
      |                   ^
../../i18n/decNumber.cpp: In function ‘uprv_decNumberSquareRoot_79’:
../../i18n/decNumber.cpp:2974:31: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 2974 |         t->lsu[0]=9; t->lsu[1]=5; t->lsu[2]=2;
      |                               ^
../../i18n/decNumber.h:89:19: note: at offset 1 into destination object ‘lsu’ of size 1
   89 |     decNumberUnit lsu[DECNUMUNITS];
      |                   ^
../../i18n/decNumber.cpp:2974:44: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 2974 |         t->lsu[0]=9; t->lsu[1]=5; t->lsu[2]=2;
      |                                            ^
../../i18n/decNumber.h:89:19: note: at offset 2 into destination object ‘lsu’ of size 1
   89 |     decNumberUnit lsu[DECNUMUNITS];
      |                   ^
../../../tools/genrb/parse.cpp: In function ‘parseIntVector’:
../../../tools/genrb/parse.cpp:1775:9: warning: ‘stringLength’ may be used uninitialized in this function [-Wmaybe-uninitialized]
 1775 |         if(len==stringLength)
      |         ^
../../../tools/genrb/parse.cpp:1762:17: note: ‘stringLength’ was declared here
 1762 |         int32_t stringLength;
      |                 ^

grhoten · 2025-11-18T06:33:27Z

Regarding one of the warnings, the warning on uprops.cpp:1022 seems to be an unreachable line, and it seems to be a bad line if it were reachable. That line should actually be setting the *pErrorCode and returning instead.

markusicu · 2025-11-21T22:56:50Z

Is the warnings discussion actually for the other PR about static initialization?

grhoten · 2025-11-22T03:11:03Z

The warnings commentary is due to this option being used. These are new warnings from g++ that I observed. It's doing a deeper analysis of the code that cross function boundaries.

jira-pull-request-webhook · 2025-11-22T03:12:55Z

Hooray! The files in the branch are the same across the force-push. 😃

~ Your Friendly Jira-GitHub PR Checker Bot

markusicu previously approved these changes Nov 6, 2025

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markusicu self-assigned this Nov 6, 2025

grhoten dismissed markusicu’s stale review via c3ee1fe November 7, 2025 05:55

grhoten force-pushed the optimization branch from c3ee1fe to 0b35d93 Compare November 7, 2025 06:42

grhoten requested a review from markusicu November 7, 2025 06:44

markusicu approved these changes Nov 21, 2025

View reviewed changes

ICU-23253 Add Link Time Optimization to release flags

bd9b80b

grhoten force-pushed the optimization branch from 63e839c to bd9b80b Compare November 22, 2025 03:12

grhoten merged commit 2a888f7 into unicode-org:main Nov 22, 2025
97 checks passed

grhoten deleted the optimization branch November 26, 2025 07:25

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