[clang] [CodeGen] Assume a for-in loop is in bounds and cannot overflow (PR #94885)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: AtariDreams (AtariDreams)

<details>
<summary>Changes</summary>

When accessing data in the buffer, we know we won't overrun the buffer, so we know it is inbounds. In addition, we know that the addition to increase the index is also NUW because the buffer's end has to be unsigned-greater-than 0, which becomes untrue if the bounds ever has an unsigned wrap.

---
Full diff: https://github.com/llvm/llvm-project/pull/94885.diff


2 Files Affected:

- (modified) clang/lib/CodeGen/CGObjC.cpp (+2-2) 
- (modified) clang/test/CodeGenObjC/arc-foreach.m (+2-2) 


``````````diff
diff --git a/clang/lib/CodeGen/CGObjC.cpp b/clang/lib/CodeGen/CGObjC.cpp
index 281b2d9795f6c..80a64d8e4cdd9 100644
--- a/clang/lib/CodeGen/CGObjC.cpp
+++ b/clang/lib/CodeGen/CGObjC.cpp
@@ -1952,7 +1952,7 @@ void CodeGenFunction::EmitObjCForCollectionStmt(const ObjCForCollectionStmt &S){
     Builder.CreateLoad(StateItemsPtr, "stateitems");
 
   // Fetch the value at the current index from the buffer.
-  llvm::Value *CurrentItemPtr = Builder.CreateGEP(
+  llvm::Value *CurrentItemPtr = Builder.CreateInBoundsGEP(
       ObjCIdType, EnumStateItems, index, "currentitem.ptr");
   llvm::Value *CurrentItem =
     Builder.CreateAlignedLoad(ObjCIdType, CurrentItemPtr, getPointerAlign());
@@ -2028,7 +2028,7 @@ void CodeGenFunction::EmitObjCForCollectionStmt(const ObjCForCollectionStmt &S){
 
   // First we check in the local buffer.
   llvm::Value *indexPlusOne =
-      Builder.CreateAdd(index, llvm::ConstantInt::get(NSUIntegerTy, 1));
+      Builder.CreateNUWAdd(index, llvm::ConstantInt::get(NSUIntegerTy, 1));
 
   // If we haven't overrun the buffer yet, we can continue.
   // Set the branch weights based on the simplifying assumption that this is
diff --git a/clang/test/CodeGenObjC/arc-foreach.m b/clang/test/CodeGenObjC/arc-foreach.m
index 71edc5161303c..9f7b60aef7a1b 100644
--- a/clang/test/CodeGenObjC/arc-foreach.m
+++ b/clang/test/CodeGenObjC/arc-foreach.m
@@ -53,7 +53,7 @@ void test0(NSArray *array) {
 
 // CHECK-LP64:      [[T0:%.*]] = getelementptr inbounds [[STATE_T]], ptr [[STATE]], i32 0, i32 1
 // CHECK-LP64-NEXT: [[T1:%.*]] = load ptr, ptr [[T0]]
-// CHECK-LP64-NEXT: [[T2:%.*]] = getelementptr ptr, ptr [[T1]], i64
+// CHECK-LP64-NEXT: [[T2:%.*]] = getelementptr inbounds ptr, ptr [[T1]], i64
 // CHECK-LP64-NEXT: [[T3:%.*]] = load ptr, ptr [[T2]]
 // CHECK-LP64-NEXT: store ptr [[T3]], ptr [[X]]
 
@@ -100,7 +100,7 @@ void test1(NSArray *array) {
 
 // CHECK-LP64:      [[T0:%.*]] = getelementptr inbounds [[STATE_T]], ptr [[STATE]], i32 0, i32 1
 // CHECK-LP64-NEXT: [[T1:%.*]] = load ptr, ptr [[T0]]
-// CHECK-LP64-NEXT: [[T2:%.*]] = getelementptr ptr, ptr [[T1]], i64
+// CHECK-LP64-NEXT: [[T2:%.*]] = getelementptr inbounds ptr, ptr [[T1]], i64
 // CHECK-LP64-NEXT: [[T3:%.*]] = load ptr, ptr [[T2]]
 // CHECK-LP64-NEXT: call ptr @llvm.objc.initWeak(ptr [[X]], ptr [[T3]])
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/94885