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[X86] Set SHF_X86_64_LARGE for globals with explicit well-known large section name (#74381)
Globals marked with the .lbss/.ldata/.lrodata should automatically be treated as large. Do this regardless of the code model for consistency when mixing object files compiled with different code models. Basically the other half of #70748. Example in the wild: https://codebrowser.dev/qt5/qtbase/src/testlib/qtestcase.cpp.html#1664
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‎llvm/lib/Target/TargetMachine.cpp

Lines changed: 21 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -43,9 +43,6 @@ bool TargetMachine::isLargeGlobalObject(const GlobalObject *GO) const {
4343
if (getTargetTriple().getArch() != Triple::x86_64)
4444
return false;
4545

46-
if (getCodeModel() != CodeModel::Medium && getCodeModel() != CodeModel::Large)
47-
return false;
48-
4946
if (isa<Function>(GO))
5047
return getCodeModel() == CodeModel::Large;
5148

@@ -54,22 +51,29 @@ bool TargetMachine::isLargeGlobalObject(const GlobalObject *GO) const {
5451
if (GV->isThreadLocal())
5552
return false;
5653

57-
// Allowing large metadata sections in the presence of an explicit section is
58-
// useful, even if GCC does not allow them. However, we should not mark
59-
// certain well-known prefixes as large, because it would make the whole
60-
// output section large and cause the linker to move it, which is almost
61-
// always undesired.
54+
// We should properly mark well-known section name prefixes as small/large,
55+
// because otherwise the output section may have the wrong section flags and
56+
// the linker will lay it out in an unexpected way.
6257
StringRef Name = GV->getSection();
63-
auto IsPrefix = [&](StringRef Prefix) {
64-
StringRef S = Name;
65-
return S.consume_front(Prefix) && (S.empty() || S[0] == '.');
66-
};
67-
if (IsPrefix(".bss") || IsPrefix(".data") || IsPrefix(".rodata"))
68-
return false;
58+
if (!Name.empty()) {
59+
auto IsPrefix = [&](StringRef Prefix) {
60+
StringRef S = Name;
61+
return S.consume_front(Prefix) && (S.empty() || S[0] == '.');
62+
};
63+
if (IsPrefix(".bss") || IsPrefix(".data") || IsPrefix(".rodata"))
64+
return false;
65+
if (IsPrefix(".lbss") || IsPrefix(".ldata") || IsPrefix(".lrodata"))
66+
return true;
67+
}
68+
69+
if (getCodeModel() == CodeModel::Medium ||
70+
getCodeModel() == CodeModel::Large) {
71+
const DataLayout &DL = GV->getParent()->getDataLayout();
72+
uint64_t Size = DL.getTypeSizeInBits(GV->getValueType()) / 8;
73+
return Size == 0 || Size > LargeDataThreshold;
74+
}
6975

70-
const DataLayout &DL = GV->getParent()->getDataLayout();
71-
uint64_t Size = DL.getTypeSizeInBits(GV->getValueType()) / 8;
72-
return Size == 0 || Size > LargeDataThreshold;
76+
return false;
7377
}
7478

7579
bool TargetMachine::isPositionIndependent() const {

‎llvm/test/CodeGen/X86/code-model-elf-sections.ll

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -21,19 +21,29 @@
2121
; SMALL: .data {{.*}} WA {{.*}}
2222
; SMALL: .data.x {{.*}} WA {{.*}}
2323
; SMALL: .data0 {{.*}} WA {{.*}}
24+
; SMALL: .ldata {{.*}} WAl {{.*}}
25+
; SMALL: .ldata.x {{.*}} WAl {{.*}}
26+
; SMALL: .ldata0 {{.*}} WA {{.*}}
2427
; SMALL: foo {{.*}} WA {{.*}}
2528
; SMALL: .bss {{.*}} WA {{.*}}
29+
; SMALL: .lbss {{.*}} WAl {{.*}}
2630
; SMALL: .rodata {{.*}} A {{.*}}
31+
; SMALL: .lrodata {{.*}} Al {{.*}}
2732
; SMALL: .data.rel.ro {{.*}} WA {{.*}}
2833
; SMALL: .tbss {{.*}} WAT {{.*}}
2934
; SMALL: .tdata {{.*}} WAT {{.*}}
3035

3136
; SMALL-DS: .data {{.*}} WA {{.*}}
3237
; SMALL-DS: .data.x {{.*}} WA {{.*}}
3338
; SMALL-DS: .data0 {{.*}} WA {{.*}}
39+
; SMALL-DS: .ldata {{.*}} WAl {{.*}}
40+
; SMALL-DS: .ldata.x {{.*}} WAl {{.*}}
41+
; SMALL-DS: .ldata0 {{.*}} WA {{.*}}
3442
; SMALL-DS: .data.data {{.*}} WA {{.*}}
3543
; SMALL-DS: foo {{.*}} WA {{.*}}
44+
; SMALL-DS: .lbss {{.*}} WAl {{.*}}
3645
; SMALL-DS: .bss.bss {{.*}} WA {{.*}}
46+
; SMALL-DS: .lrodata {{.*}} Al {{.*}}
3747
; SMALL-DS: .rodata.rodata {{.*}} A {{.*}}
3848
; SMALL-DS: .data.rel.ro.relro {{.*}} WA {{.*}}
3949
; SMALL-DS: .tbss.tbss {{.*}} WAT {{.*}}
@@ -43,6 +53,8 @@
4353
; LARGE: .data.x {{.*}} WA {{.*}}
4454
; LARGE: .data0 {{.*}} WAl {{.*}}
4555
; LARGE: .ldata {{.*}} WAl {{.*}}
56+
; LARGE: .ldata.x {{.*}} WAl {{.*}}
57+
; LARGE: .ldata0 {{.*}} WAl {{.*}}
4658
; LARGE: foo {{.*}} WAl {{.*}}
4759
; LARGE: .bss {{.*}} WA {{.*}}
4860
; LARGE: .lbss {{.*}} WAl {{.*}}
@@ -55,6 +67,9 @@
5567
; LARGE-DS: .data {{.*}} WA {{.*}}
5668
; LARGE-DS: .data.x {{.*}} WA {{.*}}
5769
; LARGE-DS: .data0 {{.*}} WAl {{.*}}
70+
; LARGE-DS: .ldata {{.*}} WAl {{.*}}
71+
; LARGE-DS: .ldata.x {{.*}} WAl {{.*}}
72+
; LARGE-DS: .ldata0 {{.*}} WAl {{.*}}
5873
; LARGE-DS: .ldata.data {{.*}} WAl {{.*}}
5974
; LARGE-DS: foo {{.*}} WAl {{.*}}
6075
; LARGE-DS: .bss {{.*}} WA {{.*}}
@@ -71,11 +86,16 @@ target triple = "x86_64--linux"
7186
@data_with_explicit_section = internal global [10 x i64] [i64 1, i64 2, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0], section ".data"
7287
@data_with_explicit_section2 = internal global [10 x i64] [i64 1, i64 2, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0], section ".data.x"
7388
@data_with_explicit_section0 = internal global [10 x i64] [i64 1, i64 2, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0], section ".data0"
89+
@ldata_with_explicit_section = internal global [10 x i64] [i64 1, i64 2, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0], section ".ldata"
90+
@ldata_with_explicit_section2 = internal global [10 x i64] [i64 1, i64 2, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0], section ".ldata.x"
91+
@ldata_with_explicit_section0 = internal global [10 x i64] [i64 1, i64 2, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0], section ".ldata0"
7492
@data = internal global [10 x i64] [i64 1, i64 2, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0]
7593
@foo_with_explicit_section = internal global [10 x i64] [i64 1, i64 2, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0, i64 0], section "foo"
7694
@bss_with_explicit_section = internal global [10 x i64] zeroinitializer, section ".bss"
95+
@lbss_with_explicit_section = internal global [10 x i64] zeroinitializer, section ".lbss"
7796
@bss = internal global [10 x i64] zeroinitializer
7897
@rodata_with_explicit_section = internal constant [10 x i64] zeroinitializer, section ".rodata"
98+
@lrodata_with_explicit_section = internal constant [10 x i64] zeroinitializer, section ".lrodata"
7999
@rodata = internal constant [10 x i64] zeroinitializer
80100
@relro = internal constant [10 x ptr] [ptr @func, ptr @func, ptr @func, ptr @func, ptr @func, ptr @func, ptr @func, ptr @func, ptr @func, ptr @func]
81101
@tbss = internal thread_local global [10 x i64] zeroinitializer

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