[llvm] [InstCombine] Fold shl of constant by cttz into multiply of lowest set bit (PR #214517)

Sun Aug 16 01:26:55 PDT 2026

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `polly-x86_64-linux-plugin` running on `polly-x86_64-gce1` while building `llvm` at step 3 "annotate".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/158/builds/19926

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 3 (annotate) failure: 'python ../llvm.src/polly/ci/polly-x86_64-linux-plugin.py ...' (failure)
...
[ 31%/473.934s :: 806->10->382 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaRISCV.cpp.o
[ 31%/474.236s :: 805->10->383 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaStmtAttr.cpp.o
[ 32%/475.497s :: 804->10->384 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaStmtAsm.cpp.o
[ 32%/485.712s :: 803->10->385 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaSystemZ.cpp.o
[ 32%/486.283s :: 802->10->386 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaSwift.cpp.o
[ 32%/487.437s :: 801->10->387 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaStmt.cpp.o
[ 32%/493.589s :: 800->10->388 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaOverload.cpp.o
[ 32%/495.759s :: 799->10->389 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaExpr.cpp.o
[ 32%/506.105s :: 798->10->390 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateVariadic.cpp.o
[ 32%/512.073s :: 797->10->391 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateInstantiateDecl.cpp.o
FAILED: tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateInstantiateDecl.cpp.o 
ccache /usr/bin/c++ -DCLANG_EXPORTS -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GLIBCXX_USE_CXX11_ABI=1 -D_GNU_SOURCE -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/build/llvm.build/tools/clang/lib/Sema -I/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/lib/Sema -I/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/include -I/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/build/llvm.build/tools/clang/include -I/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/build/llvm.build/include -I/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-dangling-reference -Wno-redundant-move -Wno-pessimizing-move -Wno-array-bounds -Wno-stringop-overread -Wno-dangling-pointer -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -fno-common -Woverloaded-virtual -O3 -DNDEBUG -std=c++17 -UNDEBUG -fno-exceptions -funwind-tables -fno-rtti -MD -MT tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateInstantiateDecl.cpp.o -MF tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateInstantiateDecl.cpp.o.d -o tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateInstantiateDecl.cpp.o -c /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp:2119:16: error: declaration of ‘clang::TemplateName SubstitutedFriend::TemplateName’ changes meaning of ‘TemplateName’ [-Wchanges-meaning]
 2119 |   TemplateName TemplateName;
      |                ^~~~~~~~~~~~
/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp:2119:3: note: used here to mean ‘class clang::TemplateName’
 2119 |   TemplateName TemplateName;
      |   ^~~~~~~~~~~~
In file included from /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/include/clang/AST/TypeBase.h:22,
                 from /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/include/clang/AST/DeclarationName.h:16,
                 from /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/include/clang/AST/DeclBase.h:19,
                 from /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/include/clang/AST/Decl.h:20,
                 from /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/lib/Sema/CoroutineStmtBuilder.h:16,
                 from /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/lib/Sema/TreeTransform.h:16,
                 from /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp:12:
/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/include/clang/AST/TemplateName.h:222:7: note: declared here
  222 | class TemplateName {
      |       ^~~~~~~~~~~~
[ 32%/514.023s :: 797->9->392 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTypeTraits.cpp.o
[ 32%/519.560s :: 797->8->393 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaSYCL.cpp.o
[ 32%/520.920s :: 797->7->394 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaWasm.cpp.o
[ 32%/525.033s :: 797->6->395 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateDeductionGuide.cpp.o
[ 33%/526.255s :: 797->5->396 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaType.cpp.o
[ 33%/528.623s :: 797->4->397 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateDeduction.cpp.o
[ 33%/533.612s :: 797->3->398 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplate.cpp.o
[ 33%/542.601s :: 797->2->399 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaOpenMP.cpp.o
[ 33%/542.943s :: 797->1->400 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateInstantiate.cpp.o
ninja: build stopped: subcommand failed.
Running: ccache -sv
Cache directory:      /srv/bbworker/.cache/ccache
Config file:          /srv/bbworker/.config/ccache/ccache.conf
System config file:   /etc/ccache.conf
Stats updated:        Sun Aug 16 08:26:38 2026
Cacheable calls:        286 / 287 (99.65%)
  Hits:                   1 / 286 ( 0.35%)
    Direct:               1 /   1 (100.0%)
    Preprocessed:         0 /   1 ( 0.00%)
  Misses:               285 / 286 (99.65%)
Uncacheable calls:        1 / 287 ( 0.35%)
Step 6 (build-llvm) failure: build-llvm (failure)
...
[ 31%/473.934s :: 806->10->382 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaRISCV.cpp.o
[ 31%/474.236s :: 805->10->383 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaStmtAttr.cpp.o
[ 32%/475.497s :: 804->10->384 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaStmtAsm.cpp.o
[ 32%/485.712s :: 803->10->385 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaSystemZ.cpp.o
[ 32%/486.283s :: 802->10->386 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaSwift.cpp.o
[ 32%/487.437s :: 801->10->387 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaStmt.cpp.o
[ 32%/493.589s :: 800->10->388 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaOverload.cpp.o
[ 32%/495.759s :: 799->10->389 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaExpr.cpp.o
[ 32%/506.105s :: 798->10->390 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateVariadic.cpp.o
[ 32%/512.073s :: 797->10->391 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateInstantiateDecl.cpp.o
FAILED: tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateInstantiateDecl.cpp.o 
ccache /usr/bin/c++ -DCLANG_EXPORTS -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GLIBCXX_USE_CXX11_ABI=1 -D_GNU_SOURCE -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/build/llvm.build/tools/clang/lib/Sema -I/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/lib/Sema -I/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/include -I/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/build/llvm.build/tools/clang/include -I/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/build/llvm.build/include -I/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-dangling-reference -Wno-redundant-move -Wno-pessimizing-move -Wno-array-bounds -Wno-stringop-overread -Wno-dangling-pointer -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -fno-common -Woverloaded-virtual -O3 -DNDEBUG -std=c++17 -UNDEBUG -fno-exceptions -funwind-tables -fno-rtti -MD -MT tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateInstantiateDecl.cpp.o -MF tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateInstantiateDecl.cpp.o.d -o tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateInstantiateDecl.cpp.o -c /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp:2119:16: error: declaration of ‘clang::TemplateName SubstitutedFriend::TemplateName’ changes meaning of ‘TemplateName’ [-Wchanges-meaning]
 2119 |   TemplateName TemplateName;
      |                ^~~~~~~~~~~~
/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp:2119:3: note: used here to mean ‘class clang::TemplateName’
 2119 |   TemplateName TemplateName;
      |   ^~~~~~~~~~~~
In file included from /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/include/clang/AST/TypeBase.h:22,
                 from /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/include/clang/AST/DeclarationName.h:16,
                 from /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/include/clang/AST/DeclBase.h:19,
                 from /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/include/clang/AST/Decl.h:20,
                 from /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/lib/Sema/CoroutineStmtBuilder.h:16,
                 from /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/lib/Sema/TreeTransform.h:16,
                 from /srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp:12:
/srv/bbworker/polly-x86_64-gce1/polly-x86_64-linux-plugin/llvm.src/clang/include/clang/AST/TemplateName.h:222:7: note: declared here
  222 | class TemplateName {
      |       ^~~~~~~~~~~~
[ 32%/514.023s :: 797->9->392 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTypeTraits.cpp.o
[ 32%/519.560s :: 797->8->393 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaSYCL.cpp.o
[ 32%/520.920s :: 797->7->394 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaWasm.cpp.o
[ 32%/525.033s :: 797->6->395 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateDeductionGuide.cpp.o
[ 33%/526.255s :: 797->5->396 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaType.cpp.o
[ 33%/528.623s :: 797->4->397 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateDeduction.cpp.o
[ 33%/533.612s :: 797->3->398 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplate.cpp.o
[ 33%/542.601s :: 797->2->399 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaOpenMP.cpp.o
[ 33%/542.943s :: 797->1->400 (of 1197)] Building CXX object tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaTemplateInstantiate.cpp.o
ninja: build stopped: subcommand failed.
Running: ccache -sv
Cache directory:      /srv/bbworker/.cache/ccache
Config file:          /srv/bbworker/.config/ccache/ccache.conf
System config file:   /etc/ccache.conf
Stats updated:        Sun Aug 16 08:26:38 2026
Cacheable calls:        286 / 287 (99.65%)
  Hits:                   1 / 286 ( 0.35%)
    Direct:               1 /   1 (100.0%)
    Preprocessed:         0 /   1 ( 0.00%)
  Misses:               285 / 286 (99.65%)
Uncacheable calls:        1 / 287 ( 0.35%)

```

</details>

https://github.com/llvm/llvm-project/pull/214517