[clang] [Clang][CodeGen] Add workaround for old glibc `__PTR_ALIGN` macro (PR #137851)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

Closes https://github.com/llvm/llvm-project/issues/137833.
This patch is stacked on https://github.com/llvm/llvm-project/pull/137849.


---
Full diff: https://github.com/llvm/llvm-project/pull/137851.diff


4 Files Affected:

- (modified) clang/lib/CodeGen/CGExpr.cpp (+3) 
- (modified) clang/lib/CodeGen/CGExprScalar.cpp (+2-1) 
- (modified) clang/test/CodeGen/catch-nullptr-and-nonzero-offset.c (+12) 
- (added) clang/test/CodeGen/glibc_ptr_align.c (+22) 


``````````diff
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index bba7d1e805f3f..e9e22321e2634 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -4820,6 +4820,9 @@ bool CodeGenFunction::isUnderlyingBasePointerConstantNull(const Expr *E) {
   const Expr *UnderlyingBaseExpr = E->IgnoreParens();
   while (auto *BaseMemberExpr = dyn_cast<MemberExpr>(UnderlyingBaseExpr))
     UnderlyingBaseExpr = BaseMemberExpr->getBase()->IgnoreParens();
+  if (auto *Select = dyn_cast<ConditionalOperator>(UnderlyingBaseExpr))
+    return isUnderlyingBasePointerConstantNull(Select->getTrueExpr()) ||
+           isUnderlyingBasePointerConstantNull(Select->getFalseExpr());
   return getContext().isSentinelNullExpr(UnderlyingBaseExpr);
 }
 
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 8dbbcdaef25d8..d214d2af52563 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -4238,7 +4238,8 @@ static Value *emitPointerArithmetic(CodeGenFunction &CGF,
   else
     elemTy = CGF.ConvertTypeForMem(elementType);
 
-  if (CGF.getLangOpts().PointerOverflowDefined)
+  if (CGF.getLangOpts().PointerOverflowDefined ||
+      CGF.isUnderlyingBasePointerConstantNull(pointerOperand))
     return CGF.Builder.CreateGEP(elemTy, pointer, index, "add.ptr");
 
   return CGF.EmitCheckedInBoundsGEP(
diff --git a/clang/test/CodeGen/catch-nullptr-and-nonzero-offset.c b/clang/test/CodeGen/catch-nullptr-and-nonzero-offset.c
index 63b6db2c2adeb..c5ae3f8bcc368 100644
--- a/clang/test/CodeGen/catch-nullptr-and-nonzero-offset.c
+++ b/clang/test/CodeGen/catch-nullptr-and-nonzero-offset.c
@@ -431,6 +431,18 @@ char *void_ptr(void *base, unsigned long offset) {
   return base + offset;
 }
 
+int *constant_null_add(long offset) {
+  // CHECK: define{{.*}} ptr @constant_null_add(i64 noundef %[[OFFSET:.*]])
+  // CHECK-NEXT: [[ENTRY:.*]]:
+  // CHECK-NEXT:   %[[OFFSET_ADDR:.*]] = alloca i64, align 8
+  // CHECK-NEXT:   store i64 %[[OFFSET]], ptr %[[OFFSET_ADDR]], align 8
+  // CHECK-NEXT:   %[[OFFSET_RELOADED:.*]] = load i64, ptr %[[OFFSET_ADDR]], align 8
+  // CHECK-NEXT:   %[[ADD_PTR:.*]] = getelementptr i32, ptr null, i64 %[[OFFSET_RELOADED]]
+  // CHECK-NEXT:   ret ptr %[[ADD_PTR]]
+#line 1800
+  return (int *)0 + offset;
+}
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/clang/test/CodeGen/glibc_ptr_align.c b/clang/test/CodeGen/glibc_ptr_align.c
new file mode 100644
index 0000000000000..14968a8326509
--- /dev/null
+++ b/clang/test/CodeGen/glibc_ptr_align.c
@@ -0,0 +1,22 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --version 5
+// RUN: %clang_cc1 -triple=x86_64-unknown-unknown -O3 -o - -emit-llvm %s | FileCheck %s
+
+// Make sure that we do not set inbounds flag if the base pointer may be a constant null.
+
+// CHECK-LABEL: define dso_local noalias ptr @glibc_ptr_align(
+// CHECK-SAME: ptr noundef readnone captures(none) [[BASE:%.*]], ptr noundef [[POINTER:%.*]], i64 noundef [[ALIGN_MASK:%.*]]) local_unnamed_addr #[[ATTR0:[0-9]+]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    [[SUB_PTR_LHS_CAST:%.*]] = ptrtoint ptr [[POINTER]] to i64
+// CHECK-NEXT:    [[ADD:%.*]] = add nsw i64 [[ALIGN_MASK]], [[SUB_PTR_LHS_CAST]]
+// CHECK-NEXT:    [[NOT:%.*]] = xor i64 [[ALIGN_MASK]], -1
+// CHECK-NEXT:    [[AND:%.*]] = and i64 [[ADD]], [[NOT]]
+// CHECK-NEXT:    [[ADD_PTR:%.*]] = getelementptr i8, ptr null, i64 [[AND]]
+// CHECK-NEXT:    ret ptr [[ADD_PTR]]
+//
+char *glibc_ptr_align(char *base, char *pointer, long align_mask) {
+  return (sizeof(long int) < sizeof(void *) ? (base) : (char *)0) +
+         (((pointer) -
+           (sizeof(long int) < sizeof(void *) ? (base) : (char *)0) +
+           (align_mask)) &
+          ~(align_mask));
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/137851