[llvm] [Attributor] Do not optimize away externally_initialized loads. (PR #128170)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Pierre van Houtryve (Pierre-vh)

<details>
<summary>Changes</summary>

Fixes SWDEV-515029

---
Full diff: https://github.com/llvm/llvm-project/pull/128170.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/IPO/Attributor.cpp (+2-1) 
- (modified) llvm/test/Transforms/Attributor/value-simplify.ll (+19) 


``````````diff
diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index a1e1a51b201b0..0865e4da1a071 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -260,7 +260,8 @@ AA::getInitialValueForObj(Attributor &A, const AbstractAttribute &QueryingAA,
       return nullptr;
   } else {
     if (!GV->hasLocalLinkage() &&
-        (GV->isInterposable() || !(GV->isConstant() && GV->hasInitializer())))
+        (GV->isInterposable() || GV->isExternallyInitialized() ||
+         !(GV->isConstant() && GV->hasInitializer())))
       return nullptr;
     if (!GV->hasInitializer())
       return UndefValue::get(&Ty);
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) }

``````````

</details>


https://github.com/llvm/llvm-project/pull/128170