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[X86] Don't respect large data threshold for globals with an explicit section #78348

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Merged
merged 3 commits into from
Jan 17, 2024
Merged

[X86] Don't respect large data threshold for globals with an explicit section #78348

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fb3d647
[X86] Don't respect large data threshold for globals with an explicit…
aeubanks Jan 16, 2024
6812b0a
refactor
aeubanks Jan 16, 2024
27fac3d
address comment
aeubanks Jan 17, 2024
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30 changes: 14 additions & 16 deletions llvm/lib/Target/TargetMachine.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -58,31 +58,29 @@ bool TargetMachine::isLargeGlobalValue(const GlobalValue *GVal) const {
if (GV->isThreadLocal())
return false;

// We should properly mark well-known section name prefixes as small/large,
// because otherwise the output section may have the wrong section flags and
// the linker will lay it out in an unexpected way.
StringRef Name = GV->getSection();
if (!Name.empty()) {
auto IsPrefix = [&](StringRef Prefix) {
StringRef S = Name;
return S.consume_front(Prefix) && (S.empty() || S[0] == '.');
};
if (IsPrefix(".bss") || IsPrefix(".data") || IsPrefix(".rodata"))
return false;
if (IsPrefix(".lbss") || IsPrefix(".ldata") || IsPrefix(".lrodata"))
return true;
}

// For x86-64, we treat an explicit GlobalVariable small code model to mean
// that the global should be placed in a small section, and ditto for large.
// Well-known section names above take precedence for correctness.
if (auto CM = GV->getCodeModel()) {
if (*CM == CodeModel::Small)
return false;
if (*CM == CodeModel::Large)
return true;
}

// Treat all globals in explicit sections as small, except for the standard
// large sections of .lbss, .ldata, .lrodata. This reduces the risk of linking
// together small and large sections, resulting in small references to large
// data sections. The code model attribute overrides this above.
if (GV->hasSection()) {
StringRef Name = GV->getSection();
auto IsPrefix = [&](StringRef Prefix) {
StringRef S = Name;
return S.consume_front(Prefix) && (S.empty() || S[0] == '.');
};
return IsPrefix(".lbss") || IsPrefix(".ldata") || IsPrefix(".lrodata");
}

// Respect large data threshold for medium and large code models.
if (getCodeModel() == CodeModel::Medium ||
getCodeModel() == CodeModel::Large) {
if (!GV->getValueType()->isSized())
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12 changes: 6 additions & 6 deletions llvm/test/CodeGen/X86/code-model-elf-sections.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -55,13 +55,13 @@

; LARGE: .data {{.*}} WA {{.*}}
; LARGE: .data.x {{.*}} WA {{.*}}
; LARGE: .data0 {{.*}} WAl {{.*}}
; LARGE: .data0 {{.*}} WA {{.*}}
; LARGE: .ldata {{.*}} WAl {{.*}}
; LARGE: .ldata.x {{.*}} WAl {{.*}}
; LARGE: .ldata0 {{.*}} WAl {{.*}}
; LARGE: .ldata0 {{.*}} WA {{.*}}
; LARGE: force_small {{.*}} WA {{.*}}
; LARGE: force_large {{.*}} WAl {{.*}}
; LARGE: foo {{.*}} WAl {{.*}}
; LARGE: foo {{.*}} WA {{.*}}
; LARGE: .bss {{.*}} WA {{.*}}
; LARGE: .lbss {{.*}} WAl {{.*}}
; LARGE: .rodata {{.*}} A {{.*}}
Expand All @@ -72,14 +72,14 @@

; LARGE-DS: .data {{.*}} WA {{.*}}
; LARGE-DS: .data.x {{.*}} WA {{.*}}
; LARGE-DS: .data0 {{.*}} WAl {{.*}}
; LARGE-DS: .data0 {{.*}} WA {{.*}}
; LARGE-DS: .ldata {{.*}} WAl {{.*}}
; LARGE-DS: .ldata.x {{.*}} WAl {{.*}}
; LARGE-DS: .ldata0 {{.*}} WAl {{.*}}
; LARGE-DS: .ldata0 {{.*}} WA {{.*}}
; LARGE-DS: .ldata.data {{.*}} WAl {{.*}}
; LARGE-DS: force_small {{.*}} WA {{.*}}
; LARGE-DS: force_large {{.*}} WAl {{.*}}
; LARGE-DS: foo {{.*}} WAl {{.*}}
; LARGE-DS: foo {{.*}} WA {{.*}}
; LARGE-DS: .bss {{.*}} WA {{.*}}
; LARGE-DS: .lbss.bss {{.*}} WAl {{.*}}
; LARGE-DS: .rodata {{.*}} A {{.*}}
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