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[Attributor] Do not optimize away externally_initialized loads. #128170

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Merged
merged 5 commits into from
Mar 3, 2025
Merged

[Attributor] Do not optimize away externally_initialized loads. #128170

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[Attributor] Do not optimize away externally_initialized loads.
Pierre-vh Feb 21, 2025
9ac5ece
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Pierre-vh Feb 21, 2025
4c712ce
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Pierre-vh Feb 24, 2025
88bc182
fix check
Pierre-vh Mar 3, 2025
5199b31
avoid assert only block
Pierre-vh Mar 3, 2025
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14 changes: 9 additions & 5 deletions llvm/lib/Transforms/IPO/Attributor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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();
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19 changes: 19 additions & 0 deletions llvm/test/Transforms/Attributor/value-simplify.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -12,13 +12,15 @@ 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
@ExtInitZeroInit = externally_initialized constant i32 zeroinitializer, align 4

;.
; CHECK: @str = private unnamed_addr addrspace(4) constant [1 x i8] zeroinitializer, align 1
; CHECK: @ConstAS3Ptr = addrspace(3) global i32 0, align 4
; 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
Expand Down Expand Up @@ -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) }
Expand Down