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[SimplifyCFG] Select the first instruction that we can handle in passingValueIsAlwaysUndefined #98802

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Jul 16, 2024
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[SimplifyCFG] Select the first instruction that we can handle in passingValueIsAlwaysUndefined #98802

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eba860d
Pre-commit test cases
dianqk Jul 13, 2024
b12417f
[SimplifyCFG] Select the first instruction that we can handle in `pas…
dianqk Jul 13, 2024
044f73f
Fix typo
dianqk Jul 14, 2024
54c058d
Address comments
dianqk Jul 14, 2024
057abc8
*v*
dianqk Jul 14, 2024
b686e35
Only check opcode in find_if
dianqk Jul 14, 2024
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28 changes: 24 additions & 4 deletions llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7573,11 +7573,31 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
return false;

if (C->isNullValue() || isa<UndefValue>(C)) {
// Only look at the first use, avoid hurting compile time with long uselists
auto *Use = cast<Instruction>(*I->user_begin());
// Only look at the first use we can handle, avoid hurting compile time with
// long uselists
auto FindUse = llvm::find_if(I->users(), [](auto *U) {
auto *Use = cast<Instruction>(U);
// Change this list when we want to add new instructions.
switch (Use->getOpcode()) {
default:
return false;
case Instruction::GetElementPtr:
case Instruction::Ret:
case Instruction::BitCast:
case Instruction::Load:
case Instruction::Store:
case Instruction::Call:
case Instruction::CallBr:
case Instruction::Invoke:
return true;
}
});
if (FindUse == I->user_end())
return false;
auto *Use = cast<Instruction>(*FindUse);
// Bail out if Use is not in the same BB as I or Use == I or Use comes
// before I in the block. The latter two can be the case if Use is a PHI
// node.
// before I in the block. The latter two can be the case if Use is a
// PHI node.
if (Use->getParent() != I->getParent() || Use == I || Use->comesBefore(I))
return false;

Expand Down
56 changes: 56 additions & 0 deletions llvm/test/Transforms/PhaseOrdering/pr98799-inline-simplifycfg-ub.ll
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@@ -0,0 +1,56 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt < %s -passes=inline,simplifycfg -S | FileCheck --check-prefix=CUSTOM %s
; RUN: opt < %s -O2 -S | FileCheck --check-prefix=O2 %s

define internal ptr @bar(ptr %arg, i1 %arg1) {
bb:
br i1 %arg1, label %bb4, label %bb2

bb2:
%i = load ptr, ptr %arg, align 8
%i3 = getelementptr inbounds i8, ptr %i, i64 1
store ptr %i3, ptr %arg, align 8
br label %bb4

bb4:
%i5 = phi ptr [ %i, %bb2 ], [ null, %bb ]
ret ptr %i5
}

define i32 @foo(ptr %arg, i1 %arg1) {
; CUSTOM-LABEL: define i32 @foo(
; CUSTOM-SAME: ptr [[ARG:%.*]], i1 [[ARG1:%.*]]) {
; CUSTOM-NEXT: [[BB:.*:]]
; CUSTOM-NEXT: [[TMP0:%.*]] = xor i1 [[ARG1]], true
; CUSTOM-NEXT: call void @llvm.assume(i1 [[TMP0]])
; CUSTOM-NEXT: [[I_I:%.*]] = load ptr, ptr [[ARG]], align 8
; CUSTOM-NEXT: [[I3_I:%.*]] = getelementptr inbounds i8, ptr [[I_I]], i64 1
; CUSTOM-NEXT: store ptr [[I3_I]], ptr [[ARG]], align 8
; CUSTOM-NEXT: [[I2:%.*]] = icmp ne ptr [[I_I]], null
; CUSTOM-NEXT: call void @llvm.assume(i1 [[I2]])
; CUSTOM-NEXT: [[I3:%.*]] = load i32, ptr [[I_I]], align 4
; CUSTOM-NEXT: ret i32 [[I3]]
;
; O2-LABEL: define i32 @foo(
; O2-SAME: ptr nocapture [[ARG:%.*]], i1 [[ARG1:%.*]]) local_unnamed_addr #[[ATTR0:[0-9]+]] {
; O2-NEXT: [[BB:.*:]]
; O2-NEXT: [[TMP0:%.*]] = xor i1 [[ARG1]], true
; O2-NEXT: tail call void @llvm.assume(i1 [[TMP0]])
; O2-NEXT: [[I_I:%.*]] = load ptr, ptr [[ARG]], align 8, !nonnull [[META0:![0-9]+]], !noundef [[META0]]
; O2-NEXT: [[I3_I:%.*]] = getelementptr inbounds i8, ptr [[I_I]], i64 1
; O2-NEXT: store ptr [[I3_I]], ptr [[ARG]], align 8
; O2-NEXT: [[I3:%.*]] = load i32, ptr [[I_I]], align 4
; O2-NEXT: ret i32 [[I3]]
;
bb:
%i = call ptr @bar(ptr %arg, i1 %arg1)
%i2 = icmp ne ptr %i, null
call void @llvm.assume(i1 %i2)
%i3 = load i32, ptr %i, align 4
ret i32 %i3
}

declare void @llvm.assume(i1)
;.
; O2: [[META0]] = !{}
;.
68 changes: 66 additions & 2 deletions llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
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Expand Up @@ -20,7 +20,7 @@ F:
define void @test2() personality ptr @__gxx_personality_v0 {
; CHECK-LABEL: @test2(
; CHECK-NEXT: entry:
; CHECK-NEXT: call void @test2() #[[ATTR3:[0-9]+]]
; CHECK-NEXT: call void @test2() #[[ATTR4:[0-9]+]]
; CHECK-NEXT: ret void
;
entry:
Expand Down Expand Up @@ -242,6 +242,8 @@ declare ptr @fn_nonnull_deref_arg(ptr nonnull dereferenceable(4) %p)
declare ptr @fn_nonnull_deref_or_null_arg(ptr nonnull dereferenceable_or_null(4) %p)
declare ptr @fn_nonnull_arg(ptr nonnull %p)
declare ptr @fn_noundef_arg(ptr noundef %p)
declare ptr @fn_ptr_arg(ptr)
declare ptr @fn_ptr_arg_nounwind_willreturn(ptr) nounwind willreturn

define void @test9(i1 %X, ptr %Y) {
; CHECK-LABEL: @test9(
Expand Down Expand Up @@ -855,10 +857,72 @@ exit:
ret i32 %res
}

; From bb to bb5 is UB.
define i32 @test9_null_user_order_1(ptr %arg, i1 %arg1, ptr %arg2) {
; CHECK-LABEL: @test9_null_user_order_1(
; CHECK-NEXT: bb:
; CHECK-NEXT: [[TMP0:%.*]] = xor i1 [[ARG1:%.*]], true
; CHECK-NEXT: call void @llvm.assume(i1 [[TMP0]])
; CHECK-NEXT: [[I:%.*]] = load ptr, ptr [[ARG:%.*]], align 8
; CHECK-NEXT: [[I4:%.*]] = getelementptr inbounds i8, ptr [[I]], i64 1
; CHECK-NEXT: store ptr [[I4]], ptr [[ARG]], align 8
; CHECK-NEXT: [[I7:%.*]] = load i32, ptr [[I]], align 4
; CHECK-NEXT: [[I8:%.*]] = icmp ne ptr [[I]], [[ARG2:%.*]]
; CHECK-NEXT: call void @fn_ptr_arg(i1 [[I8]])
; CHECK-NEXT: ret i32 [[I7]]
;
bb:
br i1 %arg1, label %bb5, label %bb3

bb3: ; preds = %bb
%i = load ptr, ptr %arg, align 8
%i4 = getelementptr inbounds i8, ptr %i, i64 1
store ptr %i4, ptr %arg, align 8
br label %bb5

bb5: ; preds = %bb3, %bb
%i6 = phi ptr [ %i, %bb3 ], [ null, %bb ]
%i7 = load i32, ptr %i6, align 4
%i8 = icmp ne ptr %i6, %arg2
call void @fn_ptr_arg(i1 %i8)
ret i32 %i7
}

define i32 @test9_null_user_order_2(ptr %arg, i1 %arg1, ptr %arg2) {
; CHECK-LABEL: @test9_null_user_order_2(
; CHECK-NEXT: bb:
; CHECK-NEXT: [[TMP0:%.*]] = xor i1 [[ARG1:%.*]], true
; CHECK-NEXT: call void @llvm.assume(i1 [[TMP0]])
; CHECK-NEXT: [[I:%.*]] = load ptr, ptr [[ARG:%.*]], align 8
; CHECK-NEXT: [[I4:%.*]] = getelementptr inbounds i8, ptr [[I]], i64 1
; CHECK-NEXT: store ptr [[I4]], ptr [[ARG]], align 8
; CHECK-NEXT: [[I8:%.*]] = icmp ne ptr [[I]], [[ARG2:%.*]]
; CHECK-NEXT: call void @fn_ptr_arg_nounwind_willreturn(i1 [[I8]])
; CHECK-NEXT: [[I7:%.*]] = load i32, ptr [[I]], align 4
; CHECK-NEXT: ret i32 [[I7]]
;
bb:
br i1 %arg1, label %bb5, label %bb3

bb3: ; preds = %bb
%i = load ptr, ptr %arg, align 8
%i4 = getelementptr inbounds i8, ptr %i, i64 1
store ptr %i4, ptr %arg, align 8
br label %bb5

bb5: ; preds = %bb3, %bb
%i6 = phi ptr [ %i, %bb3 ], [ null, %bb ]
%i8 = icmp ne ptr %i6, %arg2
call void @fn_ptr_arg_nounwind_willreturn(i1 %i8)
%i7 = load i32, ptr %i6, align 4
ret i32 %i7
}

attributes #0 = { null_pointer_is_valid }
;.
; CHECK: attributes #[[ATTR0:[0-9]+]] = { nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: write) }
; CHECK: attributes #[[ATTR1:[0-9]+]] = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
; CHECK: attributes #[[ATTR2:[0-9]+]] = { null_pointer_is_valid }
; CHECK: attributes #[[ATTR3]] = { nounwind }
; CHECK: attributes #[[ATTR3:[0-9]+]] = { nounwind willreturn }
; CHECK: attributes #[[ATTR4]] = { nounwind }
;.
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