[clang] 61a8da9 - [Clang][CodeGen] Add workaround for old glibc `__PTR_ALIGN` macro (#137851)

[via cfe-commits]

Author: Yingwei Zheng
Date: 2025-05-09T19:23:48+08:00
New Revision: 61a8da9367dc7949f36916749f6038453ea4197f

URL: https://github.com/llvm/llvm-project/commit/61a8da9367dc7949f36916749f6038453ea4197f
DIFF: https://github.com/llvm/llvm-project/commit/61a8da9367dc7949f36916749f6038453ea4197f.diff

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

This patch adds a workaround for the old glibc `__PTR_ALIGN` macro:
```
((sizeof(long int) < sizeof(void *) ? (base) : (char *)0) +
   (((pointer) - (sizeof(long int) < sizeof(void *) ? (base) : (char *)0) +
     (align_mask)) &
    ~(align_mask)));
```
Closes https://github.com/llvm/llvm-project/issues/137833.

Added: 
    clang/test/CodeGen/glibc_ptr_align.c

Modified: 
    clang/lib/AST/Expr.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index a4483a285ed4f..8557c3b82ca39 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -2247,6 +2247,16 @@ bool BinaryOperator::isNullPointerArithmeticExtension(ASTContext &Ctx,
     return false;
   }
 
+  // Workaround for old glibc's __PTR_ALIGN macro
+  if (auto *Select =
+          dyn_cast<ConditionalOperator>(PExp->IgnoreParenNoopCasts(Ctx))) {
+    // If the condition can be constant evaluated, we check the selected arm.
+    bool EvalResult;
+    if (!Select->getCond()->EvaluateAsBooleanCondition(EvalResult, Ctx))
+      return false;
+    PExp = EvalResult ? Select->getTrueExpr() : Select->getFalseExpr();
+  }
+
   // Check that the pointer is a nullptr.
   if (!PExp->IgnoreParenCasts()
           ->isNullPointerConstant(Ctx, Expr::NPC_ValueDependentIsNotNull))

diff  --git a/clang/test/CodeGen/glibc_ptr_align.c b/clang/test/CodeGen/glibc_ptr_align.c
new file mode 100644
index 0000000000000..0656d61eb0caa
--- /dev/null
+++ b/clang/test/CodeGen/glibc_ptr_align.c
@@ -0,0 +1,62 @@
+// 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 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:    [[TMP0:%.*]] = inttoptr i64 [[AND]] to ptr
+// CHECK-NEXT:    ret ptr [[TMP0]]
+//
+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));
+}
+
+// CHECK-LABEL: define dso_local ptr @glibc_ptr_align_commuted(
+// CHECK-SAME: ptr noundef readnone captures(none) [[BASE:%.*]], ptr noundef [[POINTER:%.*]], i64 noundef [[ALIGN_MASK:%.*]]) local_unnamed_addr #[[ATTR0]] {
+// 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:    [[TMP0:%.*]] = inttoptr i64 [[AND]] to ptr
+// CHECK-NEXT:    ret ptr [[TMP0]]
+//
+char *glibc_ptr_align_commuted(char *base, char *pointer, long align_mask) {
+  return (sizeof(long int) >= sizeof(void *) ? (char *)0 : (base)) +
+         (((pointer) -
+           (sizeof(long int) >= sizeof(void *) ? (char *)0 : (base)) +
+           (align_mask)) &
+          ~(align_mask));
+}
+
+// CHECK-LABEL: define dso_local ptr @glibc_ptr_align_non_constexpr(
+// CHECK-SAME: ptr noundef [[BASE:%.*]], ptr noundef [[POINTER:%.*]], i64 noundef [[ALIGN_MASK:%.*]], i32 noundef [[COND:%.*]]) local_unnamed_addr #[[ATTR0]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    [[TOBOOL_NOT:%.*]] = icmp eq i32 [[COND]], 0
+// CHECK-NEXT:    [[COND1:%.*]] = select i1 [[TOBOOL_NOT]], ptr null, ptr [[BASE]]
+// CHECK-NEXT:    [[SUB_PTR_LHS_CAST:%.*]] = ptrtoint ptr [[POINTER]] to i64
+// CHECK-NEXT:    [[SUB_PTR_RHS_CAST:%.*]] = ptrtoint ptr [[COND1]] to i64
+// CHECK-NEXT:    [[SUB_PTR_SUB:%.*]] = add i64 [[ALIGN_MASK]], [[SUB_PTR_LHS_CAST]]
+// CHECK-NEXT:    [[ADD:%.*]] = sub i64 [[SUB_PTR_SUB]], [[SUB_PTR_RHS_CAST]]
+// CHECK-NEXT:    [[NOT:%.*]] = xor i64 [[ALIGN_MASK]], -1
+// CHECK-NEXT:    [[AND:%.*]] = and i64 [[ADD]], [[NOT]]
+// CHECK-NEXT:    [[ADD_PTR:%.*]] = getelementptr inbounds i8, ptr [[COND1]], i64 [[AND]]
+// CHECK-NEXT:    ret ptr [[ADD_PTR]]
+//
+char *glibc_ptr_align_non_constexpr(char *base, char *pointer, long align_mask, int cond) {
+  return (cond ? (base) : (char *)0) +
+         (((pointer) -
+           (cond ? (base) : (char *)0) +
+           (align_mask)) &
+          ~(align_mask));
+}