Skip to content

[SROA] Allow as zext<i1> index when unfolding GEP select #146929

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 2 commits into from
Jul 4, 2025
+65 −7
Merged

[SROA] Allow as zext<i1> index when unfolding GEP select #146929

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
65dad0e
[SROA] Allow as zext<i1> index when unfolding GEP select
AlexMaclean Jul 3, 2025
83d8478
address comments
AlexMaclean Jul 4, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
31 changes: 24 additions & 7 deletions llvm/lib/Transforms/Scalar/SROA.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4070,18 +4070,27 @@ class AggLoadStoreRewriter : public InstVisitor<AggLoadStoreRewriter, bool> {
// => select cond, gep(ptr1, idx), gep(ptr2, idx)
// and gep ptr, (select cond, idx1, idx2)
// => select cond, gep(ptr, idx1), gep(ptr, idx2)
// We also allow for i1 zext indices, which are equivalent to selects.
bool unfoldGEPSelect(GetElementPtrInst &GEPI) {
// Check whether the GEP has exactly one select operand and all indices
// will become constant after the transform.
SelectInst *Sel = dyn_cast<SelectInst>(GEPI.getPointerOperand());
Instruction *Sel = dyn_cast<SelectInst>(GEPI.getPointerOperand());
for (Value *Op : GEPI.indices()) {
if (auto *SI = dyn_cast<SelectInst>(Op)) {
if (Sel)
return false;

Sel = SI;
if (!isa<ConstantInt>(Sel->getTrueValue()) ||
!isa<ConstantInt>(Sel->getFalseValue()))
if (!isa<ConstantInt>(SI->getTrueValue()) ||
!isa<ConstantInt>(SI->getFalseValue()))
return false;
continue;
}
if (auto *ZI = dyn_cast<ZExtInst>(Op)) {
if (Sel)
return false;
Sel = ZI;
if (!ZI->getSrcTy()->isIntegerTy(1))
return false;
continue;
}
Expand All @@ -4107,8 +4116,16 @@ class AggLoadStoreRewriter : public InstVisitor<AggLoadStoreRewriter, bool> {
return NewOps;
};

Value *True = Sel->getTrueValue();
Value *False = Sel->getFalseValue();
Value *Cond, *True, *False;
if (auto *SI = dyn_cast<SelectInst>(Sel)) {
Cond = SI->getCondition();
True = SI->getTrueValue();
False = SI->getFalseValue();
} else {
Cond = Sel->getOperand(0);
True = ConstantInt::get(Sel->getType(), 1);
False = ConstantInt::get(Sel->getType(), 0);
}
SmallVector<Value *> TrueOps = GetNewOps(True);
SmallVector<Value *> FalseOps = GetNewOps(False);

Expand All @@ -4123,8 +4140,8 @@ class AggLoadStoreRewriter : public InstVisitor<AggLoadStoreRewriter, bool> {
IRB.CreateGEP(Ty, FalseOps[0], ArrayRef(FalseOps).drop_front(),
False->getName() + ".sroa.gep", NW);

Value *NSel = IRB.CreateSelect(Sel->getCondition(), NTrue, NFalse,
Sel->getName() + ".sroa.sel");
Value *NSel =
IRB.CreateSelect(Cond, NTrue, NFalse, Sel->getName() + ".sroa.sel");
Visited.erase(&GEPI);
GEPI.replaceAllUsesWith(NSel);
GEPI.eraseFromParent();
Expand Down
41 changes: 41 additions & 0 deletions llvm/test/Transforms/SROA/select-gep.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -201,6 +201,47 @@ define i32 @test_select_idx_mem2reg(i1 %c) {
ret i32 %res
}

; Test gep with a select-like zext index unfolding on an alloca that is
; splittable and promotable.
define i64 @test_select_like_zext_idx_mem2reg(i1 %c) {
; CHECK-LABEL: @test_select_like_zext_idx_mem2reg(
; CHECK-NEXT: [[IDX:%.*]] = zext i1 [[C:%.*]] to i64
; CHECK-NEXT: [[RES:%.*]] = select i1 [[C]], i64 2, i64 1
; CHECK-NEXT: ret i64 [[RES]]
;
%alloca = alloca [2 x i64], align 8
store i64 1, ptr %alloca
%gep1 = getelementptr inbounds i64, ptr %alloca, i64 1
store i64 2, ptr %gep1
%idx = zext i1 %c to i64
%gep2 = getelementptr inbounds i64, ptr %alloca, i64 %idx
%res = load i64, ptr %gep2
ret i64 %res
}

; Test gep with a zext index that is not equivalent to a select. No unfolding
; or promotion should take place.
define i64 @test_zext_unlike_select_idx_mem2reg(i8 %c) {
; CHECK-LABEL: @test_zext_unlike_select_idx_mem2reg(
; CHECK-NEXT: [[ALLOCA:%.*]] = alloca [2 x i64], align 8
; CHECK-NEXT: store i64 1, ptr [[ALLOCA]], align 4
; CHECK-NEXT: [[GEP1:%.*]] = getelementptr inbounds i64, ptr [[ALLOCA]], i64 1
; CHECK-NEXT: store i64 2, ptr [[GEP1]], align 4
; CHECK-NEXT: [[IDX:%.*]] = zext i8 [[C:%.*]] to i64
; CHECK-NEXT: [[GEP2:%.*]] = getelementptr inbounds i64, ptr [[ALLOCA]], i64 [[IDX]]
; CHECK-NEXT: [[RES:%.*]] = load i64, ptr [[GEP2]], align 4
; CHECK-NEXT: ret i64 [[RES]]
;
%alloca = alloca [2 x i64], align 8
store i64 1, ptr %alloca
%gep1 = getelementptr inbounds i64, ptr %alloca, i64 1
store i64 2, ptr %gep1
%idx = zext i8 %c to i64
%gep2 = getelementptr inbounds i64, ptr %alloca, i64 %idx
%res = load i64, ptr %gep2
ret i64 %res
}

; Test gep of index select unfolding on an alloca that escaped, and as such
; is not splittable or promotable.
; FIXME: Ideally, no transform would take place in this case.
Expand Down