[Clang][CodeGen] Add workaround for old glibc __PTR_ALIGN macro
#137851
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dtcxzyw
commented
Apr 29, 2025
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@llvm/pr-subscribers-clang-codegen Author: Yingwei Zheng (dtcxzyw) ChangesCloses #137833. Full diff: https://github.com/llvm/llvm-project/pull/137851.diff 4 Files Affected:
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));
+}
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@llvm/pr-subscribers-clang Author: Yingwei Zheng (dtcxzyw) ChangesCloses #137833. Full diff: https://github.com/llvm/llvm-project/pull/137851.diff 4 Files Affected:
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));
+}
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This fixes an issue I was seeing caused by #130742 that caused GNU m4 and make builds to segfault, which I assume was caused by #137833. I don't understand the code here well enough to give an actual review, but it'd be great to see this merged as m4/make builds generating bad binaries is causing a lot of other issues. |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/190/builds/19726 Here is the relevant piece of the build log for the reference |
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Closes #137833.
This patch is stacked on #137849.