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[IR] Truncate struct field offsets exceeding the pointer index width. (#213436)

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Update accumulateConstantOffset and collectOffset to implicitly truncate
struct field offsets. This fixes crashes in the new tests, where the
field offset does not fit in the index width.

PR: https://github.com/llvm/llvm-project/pull/213436
This commit is contained in:
Florian Hahn 2026-08-01 20:09:01 +02:00 committed by GitHub
parent bd9aa3ca57
commit 6545f29f64
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GPG key ID: B5690EEEBB952194
3 changed files with 65 additions and 4 deletions
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10
llvm/lib/IR/Operator.cpp
View file

@ -192,9 +192,10 @@ bool GEPOperator::accumulateConstantOffset(
unsigned ElementIdx = ConstOffset->getZExtValue();
const StructLayout *SL = DL.getStructLayout(STy);
// Element offset is in bytes.
if (!AccumulateOffset(
APInt(Offset.getBitWidth(), SL->getElementOffset(ElementIdx)),
1))
if (!AccumulateOffset(APInt(Offset.getBitWidth(),
SL->getElementOffset(ElementIdx),
/*isSigned=*/false, /*implicitTrunc=*/true),
1))
return false;
continue;
}
@ -257,7 +258,8 @@ bool GEPOperator::collectOffset(
unsigned ElementIdx = ConstOffset->getZExtValue();
const StructLayout *SL = DL.getStructLayout(STy);
// Element offset is in bytes.
CollectConstantOffset(APInt(BitWidth, SL->getElementOffset(ElementIdx)),
CollectConstantOffset(APInt(BitWidth, SL->getElementOffset(ElementIdx),
/*isSigned=*/false, /*implicitTrunc=*/true),
1);
continue;
}

31
llvm/test/Transforms/ConstraintElimination/gep-struct-offset-index-width.ll Normal file
View file

@ -0,0 +1,31 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
; RUN: opt -passes=constraint-elimination -S %s | FileCheck %s
target datalayout = "e-m:e-p:16:16"
%s = type { [65536 x i8], i8 }
; Offset of the struct's second field does not fit into a 16 bit pointer.
define i1 @cmp_gep_struct_offset_exceeds_index_width(ptr %p) {
; CHECK-LABEL: define i1 @cmp_gep_struct_offset_exceeds_index_width(
; CHECK-SAME: ptr [[P:%.*]]) {
; CHECK-NEXT: [[A:%.*]] = getelementptr inbounds [[S:%.*]], ptr [[P]], i16 0, i32 1
; CHECK-NEXT: ret i1 false
;
%a = getelementptr inbounds %s, ptr %p, i16 0, i32 1
%c = icmp ult ptr %a, %p
ret i1 %c
}
define i1 @cmp_geps_struct_offset_exceeds_index_width(ptr %p) {
; CHECK-LABEL: define i1 @cmp_geps_struct_offset_exceeds_index_width(
; CHECK-SAME: ptr [[P:%.*]]) {
; CHECK-NEXT: [[A:%.*]] = getelementptr inbounds [[S:%.*]], ptr [[P]], i16 0, i32 1
; CHECK-NEXT: [[B:%.*]] = getelementptr inbounds i8, ptr [[P]], i16 1
; CHECK-NEXT: ret i1 true
;
%a = getelementptr inbounds %s, ptr %p, i16 0, i32 1
%b = getelementptr inbounds i8, ptr %p, i16 1
%c = icmp ult ptr %a, %b
ret i1 %c
}

28
llvm/test/Transforms/InstCombine/gep-struct-offset-index-width.ll Normal file
View file

@ -0,0 +1,28 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
; RUN: opt -passes=instcombine -S %s | FileCheck %s
target datalayout = "e-m:e-p:16:16"
%s = type { [65536 x i8], i8 }
; Offset of the struct's second field does not fit into a 16 bit pointer.
define ptr @gep_of_gep_struct_offset_exceeds_index_width(ptr %p, i16 %i) {
; CHECK-LABEL: define ptr @gep_of_gep_struct_offset_exceeds_index_width(
; CHECK-SAME: ptr [[P:%.*]], i16 [[I:%.*]]) {
; CHECK-NEXT: [[B:%.*]] = getelementptr inbounds i8, ptr [[P]], i16 [[I]]
; CHECK-NEXT: ret ptr [[B]]
;
%a = getelementptr inbounds %s, ptr %p, i16 0, i32 1
%b = getelementptr inbounds i8, ptr %a, i16 %i
ret ptr %b
}
define ptr @gep_struct_offset_exceeds_index_width_multiple(ptr %p) {
; CHECK-LABEL: define ptr @gep_struct_offset_exceeds_index_width_multiple(
; CHECK-SAME: ptr [[P:%.*]]) {
; CHECK-NEXT: ret ptr [[P]]
;
%a = getelementptr inbounds %s, ptr %p, i16 0, i32 1
%b = getelementptr inbounds %s, ptr %a, i16 0, i32 1
ret ptr %b
}