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Logging: make os_log buffer size an integer constant expression. 

The size of an os_log buffer is known at any stage of compilation, so making it
a constant expression means that the common idiom of declaring a buffer for it
won't result in a VLA. That allows the compiler to skip saving and restoring
the stack pointer around such buffers.

llvm-svn: 345828
This commit is contained in:
Tim Northover 2018-11-01 13:49:54 +00:00
parent 1546efd4a7
commit a94ecc619b
3 changed files with 15 additions and 12 deletions
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7
clang/lib/AST/ExprConstant.cpp
View File

@ -33,6 +33,7 @@
//
//===----------------------------------------------------------------------===//
#include "clang/Analysis/Analyses/OSLog.h"
#include "clang/AST/APValue.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTDiagnostic.h"
@ -8126,6 +8127,12 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
llvm_unreachable("unexpected EvalMode");
}
case Builtin::BI__builtin_os_log_format_buffer_size: {
analyze_os_log::OSLogBufferLayout Layout;
analyze_os_log::computeOSLogBufferLayout(Info.Ctx, E, Layout);
return Success(Layout.size().getQuantity(), E);
}
case Builtin::BI__builtin_bswap16:
case Builtin::BI__builtin_bswap32:
case Builtin::BI__builtin_bswap64: {

7
clang/lib/CodeGen/CGBuiltin.cpp
View File

@ -3609,13 +3609,6 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
case Builtin::BI__builtin_os_log_format:
return emitBuiltinOSLogFormat(*E);
case Builtin::BI__builtin_os_log_format_buffer_size: {
analyze_os_log::OSLogBufferLayout Layout;
analyze_os_log::computeOSLogBufferLayout(CGM.getContext(), E, Layout);
return RValue::get(ConstantInt::get(ConvertType(E->getType()),
Layout.size().getQuantity()));
}
case Builtin::BI__xray_customevent: {
if (!ShouldXRayInstrumentFunction())
return RValue::getIgnored();

13
clang/test/CodeGen/builtins.c
View File

@ -729,25 +729,28 @@ void test_builtin_os_log_merge_helper1(void *buf, unsigned u, long long ll) {
// CHECK-LABEL: define void @test_builtin_os_log_errno
void test_builtin_os_log_errno() {
// CHECK: %[[VLA:.*]] = alloca i8, i64 4, align 16
// CHECK: call void @__os_log_helper_16_2_1_0_96(i8* %[[VLA]])
// CHECK-NOT: @stacksave
// CHECK: %[[BUF:.*]] = alloca [4 x i8], align 1
// CHECK: %[[DECAY:.*]] = getelementptr inbounds [4 x i8], [4 x i8]* %[[BUF]], i32 0, i32 0
// CHECK: call void @__os_log_helper_1_2_1_0_96(i8* %[[DECAY]])
// CHECK-NOT: @stackrestore
char buf[__builtin_os_log_format_buffer_size("%m")];
__builtin_os_log_format(buf, "%m");
}
// CHECK-LABEL: define linkonce_odr hidden void @__os_log_helper_16_2_1_0_96
// CHECK-LABEL: define linkonce_odr hidden void @__os_log_helper_1_2_1_0_96
// CHECK: (i8* %[[BUFFER:.*]])
// CHECK: %[[BUFFER_ADDR:.*]] = alloca i8*, align 8
// CHECK: store i8* %[[BUFFER]], i8** %[[BUFFER_ADDR]], align 8
// CHECK: %[[BUF:.*]] = load i8*, i8** %[[BUFFER_ADDR]], align 8
// CHECK: %[[SUMMARY:.*]] = getelementptr i8, i8* %[[BUF]], i64 0
// CHECK: store i8 2, i8* %[[SUMMARY]], align 16
// CHECK: store i8 2, i8* %[[SUMMARY]], align 1
// CHECK: %[[NUMARGS:.*]] = getelementptr i8, i8* %[[BUF]], i64 1
// CHECK: store i8 1, i8* %[[NUMARGS]], align 1
// CHECK: %[[ARGDESCRIPTOR:.*]] = getelementptr i8, i8* %[[BUF]], i64 2
// CHECK: store i8 96, i8* %[[ARGDESCRIPTOR]], align 2
// CHECK: store i8 96, i8* %[[ARGDESCRIPTOR]], align 1
// CHECK: %[[ARGSIZE:.*]] = getelementptr i8, i8* %[[BUF]], i64 3
// CHECK: store i8 0, i8* %[[ARGSIZE]], align 1
// CHECK-NEXT: ret void