[llvm] 5470dff - [Attributor] Do not optimize away externally_initialized loads. (#128170)

[via llvm-commits]

Author: Pierre van Houtryve
Date: 2025-03-03T14:58:47+01:00
New Revision: 5470dffda2a197f93bf46d69c8c048c236438ef4

URL: https://github.com/llvm/llvm-project/commit/5470dffda2a197f93bf46d69c8c048c236438ef4
DIFF: https://github.com/llvm/llvm-project/commit/5470dffda2a197f93bf46d69c8c048c236438ef4.diff

LOG: [Attributor] Do not optimize away externally_initialized loads. (#128170)

Fixes SWDEV-515029

Added: 
    

Modified: 
    llvm/lib/Transforms/IPO/Attributor.cpp
    llvm/test/Transforms/Attributor/value-simplify.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index 48725a5505514..c29a5e53b82ea 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -259,11 +259,15 @@ AA::getInitialValueForObj(Attributor &A, const AbstractAttribute &QueryingAA,
     if (!Initializer)
       return nullptr;
   } else {
-    if (!GV->hasLocalLinkage() &&
-        (GV->isInterposable() || !(GV->isConstant() && GV->hasInitializer())))
-      return nullptr;
-    if (!GV->hasInitializer())
-      return UndefValue::get(&Ty);
+    if (!GV->hasLocalLinkage()) {
+      // Externally visible global that's either non-constant,
+      // or a constant with an uncertain initializer.
+      if (!GV->hasDefinitiveInitializer() || !GV->isConstant())
+        return nullptr;
+    }
+
+    // Globals with local linkage are always initialized.
+    assert(!GV->hasLocalLinkage() || GV->hasInitializer());
 
     if (!Initializer)
       Initializer = GV->getInitializer();

diff  --git a/llvm/test/Transforms/Attributor/value-simplify.ll b/llvm/test/Transforms/Attributor/value-simplify.ll
index a90fb54fbe74a..59160c0834980 100644
--- a/llvm/test/Transforms/Attributor/value-simplify.ll
+++ b/llvm/test/Transforms/Attributor/value-simplify.ll
@@ -12,6 +12,7 @@ declare ptr @llvm.call.preallocated.arg(token, i32)
 @ConstPtr = constant i32 0, align 4
 @ConstWeakPtr = weak constant i32 0, align 4
 @ConstWeakODRPtr = weak_odr constant i32 0, align 4
+ at ExtInitZeroInit = externally_initialized constant i32 zeroinitializer, align 4
 
 ;.
 ; CHECK: @str = private unnamed_addr addrspace(4) constant [1 x i8] zeroinitializer, align 1
@@ -19,6 +20,7 @@ declare ptr @llvm.call.preallocated.arg(token, i32)
 ; CHECK: @ConstPtr = constant i32 0, align 4
 ; CHECK: @ConstWeakPtr = weak constant i32 0, align 4
 ; CHECK: @ConstWeakODRPtr = weak_odr constant i32 0, align 4
+; CHECK: @ExtInitZeroInit = externally_initialized constant i32 0, align 4
 ; CHECK: @S = external global %struct.X
 ; CHECK: @g = internal constant { [2 x ptr] } { [2 x ptr] [ptr @f1, ptr @f2] }
 ; CHECK: @x = external global i32
@@ -1651,6 +1653,23 @@ define i32 @readWeakOdrConst() {
   ret i32 %l
 }
 
+define i32 @readExtInitZeroInit() {
+; TUNIT: Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none)
+; TUNIT-LABEL: define {{[^@]+}}@readExtInitZeroInit
+; TUNIT-SAME: () #[[ATTR2]] {
+; TUNIT-NEXT:    [[L:%.*]] = load i32, ptr @ExtInitZeroInit, align 4
+; TUNIT-NEXT:    ret i32 [[L]]
+;
+; CGSCC: Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none)
+; CGSCC-LABEL: define {{[^@]+}}@readExtInitZeroInit
+; CGSCC-SAME: () #[[ATTR1]] {
+; CGSCC-NEXT:    [[L:%.*]] = load i32, ptr @ExtInitZeroInit, align 4
+; CGSCC-NEXT:    ret i32 [[L]]
+;
+  %l = load i32, ptr @ExtInitZeroInit
+  ret i32 %l
+}
+
 ;.
 ; TUNIT: attributes #[[ATTR0:[0-9]+]] = { nocallback nofree nosync nounwind willreturn }
 ; TUNIT: attributes #[[ATTR1]] = { memory(readwrite, argmem: none) }