[llvm] 87f7884 - [NaryReassociate] Fix divide by zero crash in NaryReassociatePass (#202377)

[via llvm-commits]

Author: t-demchuk
Date: 2026-06-25T15:07:25+02:00
New Revision: 87f7884cb69912ca812d3a0543c94e0362d395a9

URL: https://github.com/llvm/llvm-project/commit/87f7884cb69912ca812d3a0543c94e0362d395a9
DIFF: https://github.com/llvm/llvm-project/commit/87f7884cb69912ca812d3a0543c94e0362d395a9.diff

LOG: [NaryReassociate] Fix divide by zero crash in NaryReassociatePass (#202377)

Updates NaryReassociatePass with a safety check to guard against GEPs
into arrays with zero sized element types (eg. [0 x ptr]) to prevent
division by zero.

Added: 
    llvm/test/Transforms/NaryReassociate/nary-gep-zero-sized-element.ll

Modified: 
    llvm/lib/Transforms/Scalar/NaryReassociate.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/NaryReassociate.cpp b/llvm/lib/Transforms/Scalar/NaryReassociate.cpp
index cf0d77dc11116..5bdbd3e8b47cb 100644
--- a/llvm/lib/Transforms/Scalar/NaryReassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/NaryReassociate.cpp
@@ -442,7 +442,7 @@ NaryReassociatePass::tryReassociateGEPAtIndex(GetElementPtrInst *GEP,
   // sizeof(S) = 100 is indivisible by sizeof(int64) = 8.
   //
   // TODO: bail out on this case for now. We could emit uglygep.
-  if (IndexedSize % ElementSize != 0)
+  if (ElementSize == 0 || IndexedSize % ElementSize != 0)
     return nullptr;
 
   // NewGEP = &Candidate[RHS * (sizeof(IndexedType) / sizeof(Candidate[0])));

diff  --git a/llvm/test/Transforms/NaryReassociate/nary-gep-zero-sized-element.ll b/llvm/test/Transforms/NaryReassociate/nary-gep-zero-sized-element.ll
new file mode 100644
index 0000000000000..f78023684d11f
--- /dev/null
+++ b/llvm/test/Transforms/NaryReassociate/nary-gep-zero-sized-element.ll
@@ -0,0 +1,22 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt < %s -passes=nary-reassociate -S | FileCheck %s
+
+; This test checks that NaryReassociate does not crash when a GEP's result
+; element type has a size of zero (eg. [0 x ptr] such as `%T` below).
+
+; Struct with a zero-sized field: sizeof(field 1) == 0.
+%T = type { [1 x ptr], [0 x ptr] }
+
+define ptr @foo(ptr %base, i64 %x, i64 %y) {
+; CHECK-LABEL: define ptr @foo(
+; CHECK-SAME: ptr [[BASE:%.*]], i64 [[X:%.*]], i64 [[Y:%.*]]) {
+; CHECK-NEXT:    [[Z:%.*]] = add i64 [[X]], [[Y]]
+; CHECK-NEXT:    [[GEP1:%.*]] = getelementptr [[T:%.*]], ptr [[BASE]], i64 [[X]], i32 1
+; CHECK-NEXT:    [[GEP2:%.*]] = getelementptr inbounds [[T]], ptr [[BASE]], i64 [[Z]], i32 1
+; CHECK-NEXT:    ret ptr [[GEP2]]
+;
+  %z = add i64 %x, %y
+  %gep1 = getelementptr inbounds %T, ptr %base, i64 %x, i32 1
+  %gep2 = getelementptr inbounds %T, ptr %base, i64 %z, i32 1
+  ret ptr %gep2
+}