[llvm-branch-commits] [llvm] release/20.x: [AsmPrinter] Always emit global equivalents if there is non-global uses (#145648) (PR #145690)

[via llvm-branch-commits]

https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/145690

Backport 630d55cce45f8b409367914ef372047c8c43c511

Requested by: @dianqk

>From eacbb28486642aebd28d826094301cb4ff330287 Mon Sep 17 00:00:00 2001
From: dianqk <dianqk at dianqk.net>
Date: Wed, 25 Jun 2025 18:39:36 +0800
Subject: [PATCH] [AsmPrinter] Always emit global equivalents if there is
 non-global uses (#145648)

A case found from https://github.com/rust-lang/rust/issues/142752:
https://llvm.godbolt.org/z/T7ce9saWh.

We should emit `@bar_0` for the following code:

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

@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)]
@bar_0 = internal unnamed_addr constant ptr @foo_0, align 8
@foo_0 = external global ptr, align 8

define void @foo(ptr %arg0) {
  store ptr @bar_0, ptr %arg0, align 8
  ret void
}
```

(cherry picked from commit 630d55cce45f8b409367914ef372047c8c43c511)
---
 llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp | 24 ++++++++++-----
 llvm/test/MC/X86/gotpcrel-non-globals.ll   | 36 ++++++++++++++++++++++
 2 files changed, 53 insertions(+), 7 deletions(-)
 create mode 100644 llvm/test/MC/X86/gotpcrel-non-globals.ll

diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index e77abf429e6b4..c8f567e5f4195 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -2139,16 +2139,20 @@ 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;
+  }
 
   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;
 }
@@ -2159,7 +2163,8 @@ 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.
@@ -2171,7 +2176,8 @@ 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;
 }
@@ -2189,9 +2195,13 @@ 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);
   }
diff --git a/llvm/test/MC/X86/gotpcrel-non-globals.ll b/llvm/test/MC/X86/gotpcrel-non-globals.ll
new file mode 100644
index 0000000000000..222d2d73ff728
--- /dev/null
+++ b/llvm/test/MC/X86/gotpcrel-non-globals.ll
@@ -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 at GOTPCREL+0
+; CHECK-LABEL: .Lrel_1_failed:
+; CHECK: .long   bar_1-foo_0
+; CHECK-LABEL: .Lrel_2:
+; CHECK: .long   foo_2 at GOTPCREL+0
+
+; CHECK: bar_0:
+; CHECK: bar_1:
+; CHECK: bar_2_indirect:
+
+ at 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)]
+ at 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)]
+ at 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)]
+ at bar_0 = internal unnamed_addr constant ptr @foo_0, align 8
+ at bar_1 = internal unnamed_addr constant ptr @foo_1, align 8
+ at bar_2_indirect = internal unnamed_addr constant ptr @foo_2, align 8
+ at foo_0 = external global ptr, align 8
+ at foo_1 = external global ptr, align 8
+ at 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
+}