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[AsmPrinter] Always emit global equivalents if there is non-global uses #145648

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Merged
merged 4 commits into from
Jun 25, 2025
+53 −7
Merged

[AsmPrinter] Always emit global equivalents if there is non-global uses #145648

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1e606e0
[AsmPrinter] Always emit global equivalents if there are non-global uses
dianqk Jun 25, 2025
f94a0e3
emit global variables by adding 1
dianqk Jun 25, 2025
cd85ee4
add a test case for an indirect use
dianqk Jun 25, 2025
edd82b5
typo
dianqk Jun 25, 2025
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24 changes: 17 additions & 7 deletions llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2142,16 +2142,20 @@ void AsmPrinter::emitFunctionBody() {
}

/// Compute the number of Global Variables that uses a Constant.
static unsigned getNumGlobalVariableUses(const Constant *C) {
if (!C)
static unsigned getNumGlobalVariableUses(const Constant *C,
bool &HasNonGlobalUsers) {
if (!C) {
HasNonGlobalUsers = true;
return 0;
}
Comment on lines +2147 to +2150
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I'd directly handle the case where the dyn_cast failed in the users loop instead of adding this out argument

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I think you'd still need it for the recursive case. It would be good to add a test where the extra uses are in getelementptr constant expressions.

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added in cd85ee4.


if (isa<GlobalVariable>(C))
return 1;

unsigned NumUses = 0;
for (const auto *CU : C->users())
NumUses += getNumGlobalVariableUses(dyn_cast<Constant>(CU));
NumUses +=
getNumGlobalVariableUses(dyn_cast<Constant>(CU), HasNonGlobalUsers);

return NumUses;
}
Expand All @@ -2162,7 +2166,8 @@ static unsigned getNumGlobalVariableUses(const Constant *C) {
/// candidates are skipped and are emitted later in case at least one cstexpr
/// isn't replaced by a PC relative GOT entry access.
static bool isGOTEquivalentCandidate(const GlobalVariable *GV,
unsigned &NumGOTEquivUsers) {
unsigned &NumGOTEquivUsers,
bool &HasNonGlobalUsers) {
// Global GOT equivalents are unnamed private globals with a constant
// pointer initializer to another global symbol. They must point to a
// GlobalVariable or Function, i.e., as GlobalValue.
Expand All @@ -2174,7 +2179,8 @@ static bool isGOTEquivalentCandidate(const GlobalVariable *GV,
// To be a got equivalent, at least one of its users need to be a constant
// expression used by another global variable.
for (const auto *U : GV->users())
NumGOTEquivUsers += getNumGlobalVariableUses(dyn_cast<Constant>(U));
NumGOTEquivUsers +=
getNumGlobalVariableUses(dyn_cast<Constant>(U), HasNonGlobalUsers);

return NumGOTEquivUsers > 0;
}
Expand All @@ -2192,9 +2198,13 @@ void AsmPrinter::computeGlobalGOTEquivs(Module &M) {

for (const auto &G : M.globals()) {
unsigned NumGOTEquivUsers = 0;
if (!isGOTEquivalentCandidate(&G, NumGOTEquivUsers))
bool HasNonGlobalUsers = false;
if (!isGOTEquivalentCandidate(&G, NumGOTEquivUsers, HasNonGlobalUsers))
continue;

// If non-global variables use it, we still need to emit it.
// Add 1 here, then emit it in `emitGlobalGOTEquivs`.
if (HasNonGlobalUsers)
NumGOTEquivUsers += 1;
const MCSymbol *GOTEquivSym = getSymbol(&G);
GlobalGOTEquivs[GOTEquivSym] = std::make_pair(&G, NumGOTEquivUsers);
}
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36 changes: 36 additions & 0 deletions llvm/test/MC/X86/gotpcrel-non-globals.ll
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@@ -0,0 +1,36 @@
; RUN: llc < %s | FileCheck %s

target triple = "x86_64-unknown-linux-gnu"

; Check that we emit the `@bar_*` symbols, and that we don't emit multiple symbols.

; CHECK-LABEL: .Lrel_0:
; CHECK: .long foo_0@GOTPCREL+0
; CHECK-LABEL: .Lrel_1_failed:
; CHECK: .long bar_1-foo_0
; CHECK-LABEL: .Lrel_2:
; CHECK: .long foo_2@GOTPCREL+0

; CHECK: bar_0:
; CHECK: bar_1:
; CHECK: bar_2_indirect:

@rel_0 = private unnamed_addr constant [1 x i32] [
i32 trunc (i64 sub (i64 ptrtoint (ptr @bar_0 to i64), i64 ptrtoint (ptr @rel_0 to i64)) to i32)]
@rel_1_failed = private unnamed_addr constant [1 x i32] [
i32 trunc (i64 sub (i64 ptrtoint (ptr @bar_1 to i64), i64 ptrtoint (ptr @foo_0 to i64)) to i32)]
@rel_2 = private unnamed_addr constant [1 x i32] [
i32 trunc (i64 sub (i64 ptrtoint (ptr @bar_2_indirect to i64), i64 ptrtoint (ptr @rel_2 to i64)) to i32)]
@bar_0 = internal unnamed_addr constant ptr @foo_0, align 8
@bar_1 = internal unnamed_addr constant ptr @foo_1, align 8
@bar_2_indirect = internal unnamed_addr constant ptr @foo_2, align 8
@foo_0 = external global ptr, align 8
@foo_1 = external global ptr, align 8
@foo_2 = external global ptr, align 8

define void @foo(ptr %arg0, ptr %arg1) {
store ptr @bar_0, ptr %arg0, align 8
store ptr @bar_1, ptr %arg1, align 8
store ptr getelementptr (i8, ptr @bar_2_indirect, i32 1), ptr %arg1, align 8
ret void
}