[llvm] [InstCombine] Ignore frees when inferring inbounds (PR #202304)

[Nikita Popov via llvm-commits]

https://github.com/nikic created https://github.com/llvm/llvm-project/pull/202304

>From LangRef:

> Note that the object does not have to be live anymore; being
> in-bounds of a deallocated object is sufficient.

>From 10e428527808ea3fb2c4348d9a0b6000256529f4 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Mon, 8 Jun 2026 11:54:40 +0200
Subject: [PATCH] [InstCombine] Ignore frees when inferring inbounds

>From LangRef:

> Note that the object does not have to be live anymore; being
> in-bounds of a deallocated object is sufficient.
---
 llvm/lib/Transforms/InstCombine/InstructionCombining.cpp | 4 +++-
 llvm/test/Transforms/InstCombine/inbounds-gep.ll         | 1 +
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 89bf4bf713421..608966a5e9289 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3615,7 +3615,9 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
     bool CanBeNull, CanBeFreed;
     uint64_t DerefBytes = UnderlyingPtrOp->getPointerDereferenceableBytes(
         DL, CanBeNull, CanBeFreed);
-    if (!CanBeNull && !CanBeFreed && DerefBytes != 0) {
+    // We can ignore CanBeFreed here, because inbounds is explicitly allowed to
+    // refer to a deallocated object.
+    if (!CanBeNull && DerefBytes != 0) {
       if (GEP.accumulateConstantOffset(DL, BasePtrOffset) &&
           BasePtrOffset.isNonNegative()) {
         APInt AllocSize(IdxWidth, DerefBytes);
diff --git a/llvm/test/Transforms/InstCombine/inbounds-gep.ll b/llvm/test/Transforms/InstCombine/inbounds-gep.ll
index 467e5a82f89cc..0ea71da485766 100644
--- a/llvm/test/Transforms/InstCombine/inbounds-gep.ll
+++ b/llvm/test/Transforms/InstCombine/inbounds-gep.ll
@@ -1,5 +1,6 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
 ; RUN: opt -passes=instcombine -S < %s | FileCheck %s
+; RUN: opt -passes=instcombine -use-dereferenceable-at-point-semantics -S < %s | FileCheck %s
 
 declare ptr @g()
 declare ptr @use(ptr)