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[LTO] Sort DefinedGlobals in LTO cache key #210025

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nikic merged 3 commits into from
Jul 17, 2026
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[LTO] Sort DefinedGlobals in LTO cache key #210025

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[LTO] Sort DefinedGlobals in LTO cache key
nikic Jul 16, 2026
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Add test
nikic Jul 16, 2026
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nikic Jul 17, 2026
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5 changes: 4 additions & 1 deletion llvm/lib/LTO/LTO.cpp
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Expand Up @@ -306,7 +306,10 @@ std::string llvm::computeLTOCacheKey(

// Include the hash for the linkage type to reflect internalization and weak
// resolution, and collect any used type identifier resolutions.
for (auto &GS : DefinedGlobals) {
SmallVector<std::pair<GlobalValue::GUID, GlobalValueSummary *>>

@teresajohnson teresajohnson Jul 16, 2026

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Add a comment above this about why it is needed.

SortedDefinedGlobals(DefinedGlobals.begin(), DefinedGlobals.end());
llvm::sort(SortedDefinedGlobals, llvm::less_first());
for (auto &GS : SortedDefinedGlobals) {
GlobalValue::LinkageTypes Linkage = GS.second->linkage();
Hasher.update(
ArrayRef<uint8_t>((const uint8_t *)&Linkage, sizeof(Linkage)));
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6 changes: 6 additions & 0 deletions llvm/test/ThinLTO/X86/Inputs/cache-defined-globals-order.ll
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@@ -0,0 +1,6 @@
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

define linkonce_odr void @shared29() {
ret void
}
27 changes: 27 additions & 0 deletions llvm/test/ThinLTO/X86/cache-defined-globals-order.ll
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@@ -0,0 +1,27 @@
; RUN: rm -rf %t && mkdir -p %t
; RUN: opt -module-hash -module-summary %s -o %t/t.bc
; RUN: opt -module-hash -module-summary %S/Inputs/cache-defined-globals-order.ll -o %t/a.bc

; Tests that the LTO cache key is insensitive to the order of the modules.
; The linkonce_odr function @shared29 is defined in both t.bc and a.bc, so
; it gets a different position in the combined index depending on which
; module is processed first, which results in a different insertion order
; for DefinedGlobals.

; RUN: llvm-lto2 run -cache-dir %t/cache -o %t.o %t/t.bc %t/a.bc -r=%t/t.bc,main,plx -r=%t/t.bc,shared29,plx -r=%t/a.bc,shared29,lx
; RUN: ls %t/cache | count 2

; RUN: llvm-lto2 run -cache-dir %t/cache -o %t.o %t/a.bc %t/t.bc -r=%t/t.bc,main,plx -r=%t/t.bc,shared29,plx -r=%t/a.bc,shared29,lx
; RUN: ls %t/cache | count 2

target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

define void @main() {
call void @shared29()
ret void
}

define linkonce_odr void @shared29() {
ret void
}
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