manojgupta created this revision.
manojgupta added reviewers: t.p.northover, efriedma, jyknight, chandlerc, rnk,
srhines, void.
Support for this option is needed for building Linux kernel.
This is a very frequently requested feature by kernel developers.
More details : https://lkml.org/lkml/2018/4/4/601
GCC option description for -fdelete-null-pointer-checks:
This Assume that programs cannot safely dereference null pointers,
and that no code or data element resides at address zero.
-fno-delete-null-pointer-checks is the inverse of this implying that
null pointer dereferencing is not undefined.
This feature is implemented in as the function attribute
"null-pointer-is-valid"="true".
This CL only adds the attribute on the function. Another corresponding LLVM
change updates the optimizations to not treat null pointer dereferencing
as undefined if the attribute is present.
Repository:
rC Clang
https://reviews.llvm.org/D47894
Files:
include/clang/Driver/Options.td
include/clang/Frontend/CodeGenOptions.def
lib/CodeGen/CGCall.cpp
lib/Driver/ToolChains/Clang.cpp
lib/Frontend/CompilerInvocation.cpp
test/CodeGen/delete-null-pointer-checks.c
test/Driver/clang_f_opts.c
Index: test/Driver/clang_f_opts.c
===================================================================
--- test/Driver/clang_f_opts.c
+++ test/Driver/clang_f_opts.c
@@ -348,7 +348,6 @@
// RUN: -fwhole-program \
// RUN: -fcaller-saves \
// RUN: -freorder-blocks \
-// RUN: -fdelete-null-pointer-checks \
// RUN: -ffat-lto-objects \
// RUN: -fmerge-constants \
// RUN: -finline-small-functions \
@@ -414,7 +413,6 @@
// CHECK-WARNING-DAG: optimization flag '-fwhole-program' is not supported
// CHECK-WARNING-DAG: optimization flag '-fcaller-saves' is not supported
// CHECK-WARNING-DAG: optimization flag '-freorder-blocks' is not supported
-// CHECK-WARNING-DAG: optimization flag '-fdelete-null-pointer-checks' is not supported
// CHECK-WARNING-DAG: optimization flag '-ffat-lto-objects' is not supported
// CHECK-WARNING-DAG: optimization flag '-fmerge-constants' is not supported
// CHECK-WARNING-DAG: optimization flag '-finline-small-functions' is not supported
@@ -526,3 +524,10 @@
// RUN: %clang -### -S -fno-merge-all-constants -fmerge-all-constants %s 2>&1 | FileCheck -check-prefix=CHECK-MERGE-ALL-CONSTANTS %s
// CHECK-NO-MERGE-ALL-CONSTANTS-NOT: "-fmerge-all-constants"
// CHECK-MERGE-ALL-CONSTANTS: "-fmerge-all-constants"
+
+// RUN: %clang -### -S -fdelete-null-pointer-checks %s 2>&1 | FileCheck -check-prefix=CHECK-NULL-POINTER-CHECKS %s
+// RUN: %clang -### -S -fno-delete-null-pointer-checks %s 2>&1 | FileCheck -check-prefix=CHECK-NO-NULL-POINTER-CHECKS %s
+// RUN: %clang -### -S -fdelete-null-pointer-checks -fno-delete-null-pointer-checks %s 2>&1 | FileCheck -check-prefix=CHECK-NO-NULL-POINTER-CHECKS %s
+// RUN: %clang -### -S -fno-delete-null-pointer-checks -fdelete-null-pointer-checks %s 2>&1 | FileCheck -check-prefix=CHECK-NULL-POINTER-CHECKS %s
+// CHECK-NO-NULL-POINTER-CHECKS: "-fno-delete-null-pointer-checks"
+// CHECK-NULL-POINTER-CHECKS-NOT: "-fno-delete-null-pointer-checks"
Index: test/CodeGen/delete-null-pointer-checks.c
===================================================================
--- /dev/null
+++ test/CodeGen/delete-null-pointer-checks.c
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -emit-llvm -o - %s | FileCheck -check-prefix=NULL-POINTER-INVALID %s
+// RUN: %clang_cc1 -emit-llvm -o - %s -fno-delete-null-pointer-checks | FileCheck -check-prefix=NULL-POINTER-VALID %s
+
+int test1(int a) {
+ return a;
+}
+
+// NULL-POINTER-INVALID-NOT: attributes #0 = {{.*}} "null-pointer-is-valid"="true"
+// NULL-POINTER-VALID: attributes #0 = {{.*}} "null-pointer-is-valid"="true"
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -742,6 +742,7 @@
OPT_fno_unique_section_names, true);
Opts.MergeFunctions = Args.hasArg(OPT_fmerge_functions);
+ Opts.NullPointerIsValid = Args.hasArg(OPT_fno_delete_null_pointer_checks);
Opts.NoUseJumpTables = Args.hasArg(OPT_fno_jump_tables);
Index: lib/Driver/ToolChains/Clang.cpp
===================================================================
--- lib/Driver/ToolChains/Clang.cpp
+++ lib/Driver/ToolChains/Clang.cpp
@@ -3382,6 +3382,10 @@
options::OPT_fno_merge_all_constants, false))
CmdArgs.push_back("-fmerge-all-constants");
+ if (Args.hasFlag(options::OPT_fno_delete_null_pointer_checks,
+ options::OPT_fdelete_null_pointer_checks, false))
+ CmdArgs.push_back("-fno-delete-null-pointer-checks");
+
// LLVM Code Generator Options.
if (Args.hasArg(options::OPT_frewrite_map_file) ||
Index: lib/CodeGen/CGCall.cpp
===================================================================
--- lib/CodeGen/CGCall.cpp
+++ lib/CodeGen/CGCall.cpp
@@ -1721,6 +1721,8 @@
FuncAttrs.addAttribute("less-precise-fpmad",
llvm::toStringRef(CodeGenOpts.LessPreciseFPMAD));
+ if (CodeGenOpts.NullPointerIsValid)
+ FuncAttrs.addAttribute("null-pointer-is-valid", "true");
if (!CodeGenOpts.FPDenormalMode.empty())
FuncAttrs.addAttribute("denormal-fp-math", CodeGenOpts.FPDenormalMode);
Index: include/clang/Frontend/CodeGenOptions.def
===================================================================
--- include/clang/Frontend/CodeGenOptions.def
+++ include/clang/Frontend/CodeGenOptions.def
@@ -130,6 +130,7 @@
CODEGENOPT(NoImplicitFloat , 1, 0) ///< Set when -mno-implicit-float is enabled.
CODEGENOPT(NoInfsFPMath , 1, 0) ///< Assume FP arguments, results not +-Inf.
CODEGENOPT(NoSignedZeros , 1, 0) ///< Allow ignoring the signedness of FP zero
+CODEGENOPT(NullPointerIsValid , 1, 0) ///< Assume Null pointer deference is defined.
CODEGENOPT(Reassociate , 1, 0) ///< Allow reassociation of FP math ops
CODEGENOPT(ReciprocalMath , 1, 0) ///< Allow FP divisions to be reassociated.
CODEGENOPT(NoTrappingMath , 1, 0) ///< Set when -fno-trapping-math is enabled.
Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -1073,6 +1073,12 @@
Flags<[CC1Option]>;
def fno_rewrite_imports : Flag<["-"], "fno-rewrite-imports">, Group<f_Group>;
+def fdelete_null_pointer_checks : Flag<["-"],
+ "fdelete-null-pointer-checks">, Group<f_Group>;
+def fno_delete_null_pointer_checks : Flag<["-"],
+ "fno-delete-null-pointer-checks">, Group<f_Group>, Flags<[CC1Option]>,
+ HelpText<"Assume that null pointer dereferences are not undefined">;
+
def frewrite_map_file : Separate<["-"], "frewrite-map-file">,
Group<f_Group>,
Flags<[ DriverOption, CC1Option ]>;
@@ -2829,8 +2835,6 @@
defm eliminate_unused_debug_types : BooleanFFlag<"eliminate-unused-debug-types">, Group<clang_ignored_f_Group>;
defm branch_count_reg : BooleanFFlag<"branch-count-reg">, Group<clang_ignored_gcc_optimization_f_Group>;
defm default_inline : BooleanFFlag<"default-inline">, Group<clang_ignored_gcc_optimization_f_Group>;
-defm delete_null_pointer_checks : BooleanFFlag<"delete-null-pointer-checks">,
- Group<clang_ignored_gcc_optimization_f_Group>;
defm fat_lto_objects : BooleanFFlag<"fat-lto-objects">, Group<clang_ignored_gcc_optimization_f_Group>;
defm float_store : BooleanFFlag<"float-store">, Group<clang_ignored_gcc_optimization_f_Group>;
defm friend_injection : BooleanFFlag<"friend-injection">, Group<clang_ignored_f_Group>;
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