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[llvm] Fix __builtin_object_size interaction between Negative Offset and Select/Phi
When picking a SizeOffsetAPInt through combineSizeOffset, the behavior differs if we're going to apply a constant offset that's positive or negative: If it's positive, then we need to compare the remaining bytes (i.e. Size - Offset), but if it's negative, we need to compare the preceding bytes (i.e. Offset). Fix #111709
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3 files changed

+154
-13
lines changed

3 files changed

+154
-13
lines changed

‎llvm/include/llvm/Analysis/MemoryBuiltins.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -160,6 +160,7 @@ struct ObjectSizeOpts {
160160
/// though they can't be evaluated. Otherwise, null is always considered to
161161
/// point to a 0 byte region of memory.
162162
bool NullIsUnknownSize = false;
163+
163164
/// If set, used for more accurate evaluation
164165
AAResults *AA = nullptr;
165166
};
@@ -230,6 +231,7 @@ class ObjectSizeOffsetVisitor
230231
ObjectSizeOpts Options;
231232
unsigned IntTyBits;
232233
APInt Zero;
234+
APInt ConstantOffset;
233235
SmallDenseMap<Instruction *, SizeOffsetAPInt, 8> SeenInsts;
234236
unsigned InstructionsVisited;
235237

‎llvm/lib/Analysis/MemoryBuiltins.cpp

Lines changed: 45 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -570,6 +570,14 @@ static APInt getSizeWithOverflow(const SizeOffsetAPInt &Data) {
570570
return Size - Offset;
571571
}
572572

573+
static APInt getOffsetWithOverflow(const SizeOffsetAPInt &Data) {
574+
APInt Size = Data.Size;
575+
APInt Offset = Data.Offset;
576+
if (Offset.isNegative())
577+
return APInt(Size.getBitWidth(), 0);
578+
return Offset;
579+
}
580+
573581
/// Compute the size of the object pointed by Ptr. Returns true and the
574582
/// object size in Size if successful, and false otherwise.
575583
/// If RoundToAlign is true, then Size is rounded up to the alignment of
@@ -697,7 +705,8 @@ SizeOffsetAPInt ObjectSizeOffsetVisitor::computeImpl(Value *V) {
697705
// the index type size and if we stripped address space casts we have to
698706
// readjust the APInt as we pass it upwards in order for the APInt to match
699707
// the type the caller passed in.
700-
APInt Offset(InitialIntTyBits, 0);
708+
709+
APInt Offset = APInt{InitialIntTyBits, 0};
701710
V = V->stripAndAccumulateConstantOffsets(
702711
DL, Offset, /* AllowNonInbounds */ true, /* AllowInvariantGroup */ true);
703712

@@ -706,7 +715,9 @@ SizeOffsetAPInt ObjectSizeOffsetVisitor::computeImpl(Value *V) {
706715
IntTyBits = DL.getIndexTypeSizeInBits(V->getType());
707716
Zero = APInt::getZero(IntTyBits);
708717

718+
std::swap(Offset, ConstantOffset);
709719
SizeOffsetAPInt SOT = computeValue(V);
720+
std::swap(Offset, ConstantOffset);
710721

711722
bool IndexTypeSizeChanged = InitialIntTyBits != IntTyBits;
712723
if (!IndexTypeSizeChanged && Offset.isZero())
@@ -981,18 +992,39 @@ ObjectSizeOffsetVisitor::combineSizeOffset(SizeOffsetAPInt LHS,
981992
SizeOffsetAPInt RHS) {
982993
if (!LHS.bothKnown() || !RHS.bothKnown())
983994
return ObjectSizeOffsetVisitor::unknown();
984-
985-
switch (Options.EvalMode) {
986-
case ObjectSizeOpts::Mode::Min:
987-
return (getSizeWithOverflow(LHS).slt(getSizeWithOverflow(RHS))) ? LHS : RHS;
988-
case ObjectSizeOpts::Mode::Max:
989-
return (getSizeWithOverflow(LHS).sgt(getSizeWithOverflow(RHS))) ? LHS : RHS;
990-
case ObjectSizeOpts::Mode::ExactSizeFromOffset:
991-
return (getSizeWithOverflow(LHS).eq(getSizeWithOverflow(RHS)))
992-
? LHS
993-
: ObjectSizeOffsetVisitor::unknown();
994-
case ObjectSizeOpts::Mode::ExactUnderlyingSizeAndOffset:
995-
return LHS == RHS ? LHS : ObjectSizeOffsetVisitor::unknown();
995+
// If the ConstantOffset we add in the end is negative, then we're actually
996+
// interested in selecting the nodes based on their offset rather than their
997+
// size.
998+
if (ConstantOffset.isNegative()) {
999+
switch (Options.EvalMode) {
1000+
case ObjectSizeOpts::Mode::Min:
1001+
return (getOffsetWithOverflow(LHS).slt(getOffsetWithOverflow(RHS))) ? LHS
1002+
: RHS;
1003+
case ObjectSizeOpts::Mode::Max:
1004+
return (getOffsetWithOverflow(LHS).sgt(getOffsetWithOverflow(RHS))) ? LHS
1005+
: RHS;
1006+
case ObjectSizeOpts::Mode::ExactSizeFromOffset:
1007+
return (getOffsetWithOverflow(LHS).eq(getOffsetWithOverflow(RHS)))
1008+
? LHS
1009+
: ObjectSizeOffsetVisitor::unknown();
1010+
case ObjectSizeOpts::Mode::ExactUnderlyingSizeAndOffset:
1011+
return LHS == RHS ? LHS : ObjectSizeOffsetVisitor::unknown();
1012+
}
1013+
} else {
1014+
switch (Options.EvalMode) {
1015+
case ObjectSizeOpts::Mode::Min:
1016+
return (getSizeWithOverflow(LHS).slt(getSizeWithOverflow(RHS))) ? LHS
1017+
: RHS;
1018+
case ObjectSizeOpts::Mode::Max:
1019+
return (getSizeWithOverflow(LHS).sgt(getSizeWithOverflow(RHS))) ? LHS
1020+
: RHS;
1021+
case ObjectSizeOpts::Mode::ExactSizeFromOffset:
1022+
return (getSizeWithOverflow(LHS).eq(getSizeWithOverflow(RHS)))
1023+
? LHS
1024+
: ObjectSizeOffsetVisitor::unknown();
1025+
case ObjectSizeOpts::Mode::ExactUnderlyingSizeAndOffset:
1026+
return LHS == RHS ? LHS : ObjectSizeOffsetVisitor::unknown();
1027+
}
9961028
}
9971029
llvm_unreachable("missing an eval mode");
9981030
}

‎llvm/test/Transforms/LowerConstantIntrinsics/builtin-object-size-phi.ll

Lines changed: 107 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -117,3 +117,110 @@ if.end:
117117
%size = call i64 @llvm.objectsize.i64.p0(ptr %p, i1 true, i1 true, i1 false)
118118
ret i64 %size
119119
}
120+
121+
define i64 @pick_negative_offset(i32 %n) {
122+
; CHECK-LABEL: @pick_negative_offset(
123+
; CHECK-NEXT: entry:
124+
; CHECK-NEXT: [[BUFFER0:%.*]] = alloca i8, i64 20, align 1
125+
; CHECK-NEXT: [[OFFSETED0:%.*]] = getelementptr i8, ptr [[BUFFER0]], i64 20
126+
; CHECK-NEXT: [[COND:%.*]] = icmp eq i32 [[N:%.*]], 0
127+
; CHECK-NEXT: br i1 [[COND]], label [[IF_ELSE:%.*]], label [[IF_END:%.*]]
128+
; CHECK: if.else:
129+
; CHECK-NEXT: [[BUFFER1:%.*]] = alloca i8, i64 20, align 1
130+
; CHECK-NEXT: [[OFFSETED1:%.*]] = getelementptr i8, ptr [[BUFFER1]], i64 20
131+
; CHECK-NEXT: br label [[IF_END]]
132+
; CHECK: if.end:
133+
; CHECK-NEXT: [[P:%.*]] = phi ptr [ [[OFFSETED1]], [[IF_ELSE]] ], [ [[OFFSETED0]], [[ENTRY:%.*]] ]
134+
; CHECK-NEXT: [[POFFSETED:%.*]] = getelementptr i8, ptr [[P]], i64 -4
135+
; CHECK-NEXT: ret i64 4
136+
;
137+
entry:
138+
%buffer0 = alloca i8, i64 20
139+
%offseted0 = getelementptr i8, ptr %buffer0, i64 20
140+
%cond = icmp eq i32 %n, 0
141+
br i1 %cond, label %if.else, label %if.end
142+
143+
if.else:
144+
%buffer1 = alloca i8, i64 20
145+
%offseted1 = getelementptr i8, ptr %buffer1, i64 20
146+
br label %if.end
147+
148+
if.end:
149+
%p = phi ptr [ %offseted1, %if.else ], [ %offseted0, %entry ]
150+
%poffseted = getelementptr i8, ptr %p, i64 -4
151+
%size = call i64 @llvm.objectsize.i64.p0(ptr %poffseted, i1 false, i1 false, i1 false)
152+
ret i64 %size
153+
}
154+
155+
define i64 @pick_negative_offset_with_nullptr(i32 %n) {
156+
; CHECK-LABEL: @pick_negative_offset_with_nullptr(
157+
; CHECK-NEXT: entry:
158+
; CHECK-NEXT: [[BUFFER0:%.*]] = alloca i8, i64 20, align 1
159+
; CHECK-NEXT: [[OFFSETED0:%.*]] = getelementptr i8, ptr [[BUFFER0]], i64 20
160+
; CHECK-NEXT: [[COND:%.*]] = icmp eq i32 [[N:%.*]], 0
161+
; CHECK-NEXT: br i1 [[COND]], label [[IF_ELSE:%.*]], label [[IF_END:%.*]]
162+
; CHECK: if.else:
163+
; CHECK-NEXT: br label [[IF_END]]
164+
; CHECK: if.end:
165+
; CHECK-NEXT: [[P0:%.*]] = phi ptr [ [[OFFSETED0]], [[ENTRY:%.*]] ], [ null, [[IF_ELSE]] ]
166+
; CHECK-NEXT: [[P1:%.*]] = phi ptr [ null, [[IF_ELSE]] ], [ [[OFFSETED0]], [[ENTRY]] ]
167+
; CHECK-NEXT: [[P0OFFSETED:%.*]] = getelementptr i8, ptr [[P0]], i64 -4
168+
; CHECK-NEXT: [[P1OFFSETED:%.*]] = getelementptr i8, ptr [[P1]], i64 -4
169+
; CHECK-NEXT: [[SIZE:%.*]] = select i1 [[COND]], i64 0, i64 4
170+
; CHECK-NEXT: ret i64 [[SIZE]]
171+
;
172+
entry:
173+
%buffer0 = alloca i8, i64 20
174+
%offseted0 = getelementptr i8, ptr %buffer0, i64 20
175+
%cond = icmp eq i32 %n, 0
176+
br i1 %cond, label %if.else, label %if.end
177+
178+
if.else:
179+
br label %if.end
180+
181+
if.end:
182+
%p0 = phi ptr [ %offseted0, %entry ], [ null, %if.else ]
183+
%p1 = phi ptr [ null, %if.else ], [ %offseted0, %entry ]
184+
%p0offseted = getelementptr i8, ptr %p0, i64 -4
185+
%p1offseted = getelementptr i8, ptr %p1, i64 -4
186+
%size0 = call i64 @llvm.objectsize.i64.p0(ptr %p0offseted, i1 false, i1 false, i1 false)
187+
%size1 = call i64 @llvm.objectsize.i64.p0(ptr %p1offseted, i1 false, i1 false, i1 false)
188+
%size = select i1 %cond, i64 %size0, i64 %size1
189+
ret i64 %size
190+
}
191+
192+
define i64 @pick_negative_offset_with_unsized_nullptr(i32 %n) {
193+
; CHECK-LABEL: @pick_negative_offset_with_unsized_nullptr(
194+
; CHECK-NEXT: entry:
195+
; CHECK-NEXT: [[BUFFER0:%.*]] = alloca i8, i64 20, align 1
196+
; CHECK-NEXT: [[OFFSETED0:%.*]] = getelementptr i8, ptr [[BUFFER0]], i64 20
197+
; CHECK-NEXT: [[COND:%.*]] = icmp eq i32 [[N:%.*]], 0
198+
; CHECK-NEXT: br i1 [[COND]], label [[IF_ELSE:%.*]], label [[IF_END:%.*]]
199+
; CHECK: if.else:
200+
; CHECK-NEXT: br label [[IF_END]]
201+
; CHECK: if.end:
202+
; CHECK-NEXT: [[P0:%.*]] = phi ptr [ [[OFFSETED0]], [[ENTRY:%.*]] ], [ null, [[IF_ELSE]] ]
203+
; CHECK-NEXT: [[P1:%.*]] = phi ptr [ null, [[IF_ELSE]] ], [ [[OFFSETED0]], [[ENTRY]] ]
204+
; CHECK-NEXT: [[P0OFFSETED:%.*]] = getelementptr i8, ptr [[P0]], i64 -4
205+
; CHECK-NEXT: [[P1OFFSETED:%.*]] = getelementptr i8, ptr [[P1]], i64 -4
206+
; CHECK-NEXT: ret i64 -1
207+
;
208+
entry:
209+
%buffer0 = alloca i8, i64 20
210+
%offseted0 = getelementptr i8, ptr %buffer0, i64 20
211+
%cond = icmp eq i32 %n, 0
212+
br i1 %cond, label %if.else, label %if.end
213+
214+
if.else:
215+
br label %if.end
216+
217+
if.end:
218+
%p0 = phi ptr [ %offseted0, %entry ], [ null, %if.else ]
219+
%p1 = phi ptr [ null, %if.else ], [ %offseted0, %entry ]
220+
%p0offseted = getelementptr i8, ptr %p0, i64 -4
221+
%p1offseted = getelementptr i8, ptr %p1, i64 -4
222+
%size0 = call i64 @llvm.objectsize.i64.p0(ptr %p0offseted, i1 false, i1 true, i1 false)
223+
%size1 = call i64 @llvm.objectsize.i64.p0(ptr %p1offseted, i1 false, i1 true, i1 false)
224+
%size = select i1 %cond, i64 %size0, i64 %size1
225+
ret i64 %size
226+
}

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