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[Driver][X86] Add -mpad-max-prefix-size 

Summary:
The option `-mpad-max-prefix-size` performs some checking and delegate to MC option `-x86-pad-max-prefix-size`. This option is designed for eliminate NOPs when we need to align something by adding redundant prefixes to instructions, e.g. it can be used along with `-malign-branch`, `-malign-branch-boundary` to prefix padding branch.

It has similar (but slightly different) effect as GAS's option `-malign-branch-prefix-size`, e.g. `-mpad-max-prefix-size` can also elminate NOPs emitted by align directive, so we use a different name here. I remove the option `-malign-branch-prefix-size` since is unimplemented and not needed. If we need to be compatible with GAS, we can make `-malign-branch-prefix-size` an alias for this option later.

Reviewers: jyknight, reames, MaskRay, craig.topper, LuoYuanke

Reviewed By: MaskRay, LuoYuanke

Subscribers: annita.zhang, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D77628
This commit is contained in:
Shengchen Kan 2020-04-07 12:25:03 +08:00
parent f355e15104
commit 792b10978d
4 changed files with 14 additions and 17 deletions
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3
clang/include/clang/Driver/Options.td
View File

@ -2187,7 +2187,8 @@ def malign_branch_EQ : CommaJoined<["-"], "malign-branch=">, Group<m_Group>, Fla
HelpText<"Specify types of branches to align">;
def malign_branch_boundary_EQ : Joined<["-"], "malign-branch-boundary=">, Group<m_Group>, Flags<[DriverOption]>,
HelpText<"Specify the boundary's size to align branches">;
def malign_branch_prefix_size_EQ : Joined<["-"], "malign-branch-prefix-size=">, Group<m_Group>;
def mpad_max_prefix_size_EQ : Joined<["-"], "mpad-max-prefix-size=">, Group<m_Group>, Flags<[DriverOption]>,
HelpText<"Specify maximum number of prefixes to use for padding">;
def mbranches_within_32B_boundaries : Flag<["-"], "mbranches-within-32B-boundaries">, Flags<[DriverOption]>, Group<m_Group>,
HelpText<"Align selected branches (fused, jcc, jmp) within 32-byte boundary">;
def mfancy_math_387 : Flag<["-"], "mfancy-math-387">, Group<clang_ignored_m_Group>;

9
clang/lib/Driver/ToolChains/Clang.cpp
View File

@ -2078,17 +2078,16 @@ static void addX86AlignBranchArgs(const Driver &D, const ArgList &Args,
CmdArgs.push_back("-mllvm");
CmdArgs.push_back(Args.MakeArgString("-x86-align-branch=" + AlignBranch));
}
if (const Arg *A =
Args.getLastArg(options::OPT_malign_branch_prefix_size_EQ)) {
if (const Arg *A = Args.getLastArg(options::OPT_mpad_max_prefix_size_EQ)) {
StringRef Value = A->getValue();
unsigned PrefixSize;
if (Value.getAsInteger(10, PrefixSize) || PrefixSize > 5) {
if (Value.getAsInteger(10, PrefixSize)) {
D.Diag(diag::err_drv_invalid_argument_to_option)
<< Value << A->getOption().getName();
} else {
CmdArgs.push_back("-mllvm");
CmdArgs.push_back(Args.MakeArgString("-x86-align-branch-prefix-size=" +
Twine(PrefixSize)));
CmdArgs.push_back(
Args.MakeArgString("-x86-pad-max-prefix-size=" + Twine(PrefixSize)));
}
}
}

15
clang/test/Driver/x86-malign-branch.c
View File

@ -18,14 +18,11 @@
// TYPE-ERR: invalid argument 'foo' to -malign-branch=; each element must be one of: fused, jcc, jmp, call, ret, indirect
// TYPE-ERR: invalid argument 'bar' to -malign-branch=; each element must be one of: fused, jcc, jmp, call, ret, indirect
/// Test -malign-branch-prefix-size=
// RUN: %clang -target x86_64 -malign-branch-prefix-size=0 %s -c -### 2>&1 | FileCheck %s --check-prefix=PREFIX-0
// PREFIX-0: "-mllvm" "-x86-align-branch-prefix-size=0"
// RUN: %clang -target x86_64 -malign-branch-prefix-size=5 %s -c -### 2>&1 | FileCheck %s --check-prefix=PREFIX-5
// PREFIX-5: "-mllvm" "-x86-align-branch-prefix-size=5"
// RUN: %clang -target x86_64 -malign-branch-prefix-size=6 %s -c -### 2>&1 | FileCheck %s --check-prefix=PREFIX-6
// PREFIX-6: invalid argument
/// Test -mpad-max-prefix-size=
// RUN: %clang -target x86_64 -mpad-max-prefix-size=0 %s -c -### 2>&1 | FileCheck %s --check-prefix=PREFIX-0
// PREFIX-0: "-mllvm" "-x86-pad-max-prefix-size=0"
// RUN: %clang -target x86_64 -mpad-max-prefix-size=15 %s -c -### 2>&1 | FileCheck %s --check-prefix=PREFIX-15
// PREFIX-15: "-mllvm" "-x86-pad-max-prefix-size=15"
/// Test -mbranches-within-32B-boundaries
// RUN: %clang -target x86_64 -mbranches-within-32B-boundaries %s -c -### 2>&1 | FileCheck %s --check-prefix=32B
@ -34,6 +31,6 @@
/// Unsupported on other targets.
// RUN: %clang -target aarch64 -malign-branch=jmp %s -c -### 2>&1 | FileCheck --check-prefix=UNUSED %s
// RUN: %clang -target aarch64 -malign-branch-boundary=7 %s -c -### 2>&1 | FileCheck --check-prefix=UNUSED %s
// RUN: %clang -target aarch64 -malign-branch-prefix-size=15 %s -c -### 2>&1 | FileCheck --check-prefix=UNUSED %s
// RUN: %clang -target aarch64 -mpad-max-prefix-size=15 %s -c -### 2>&1 | FileCheck --check-prefix=UNUSED %s
// RUN: %clang -target aarch64 -mbranches-within-32B-boundaries %s -c -### 2>&1 | FileCheck --check-prefix=UNUSED %s
// UNUSED: warning: argument unused

4
clang/test/Driver/x86-malign-branch.s
View File

@ -6,8 +6,8 @@
// RUN: %clang -target x86_64 -malign-branch=fused,jcc,jmp %s -c -### %s 2>&1 | FileCheck %s --check-prefix=TYPE
// TYPE: "-mllvm" "-x86-align-branch=fused+jcc+jmp"
// RUN: %clang -target x86_64 -malign-branch-prefix-size=5 %s -c -### 2>&1 | FileCheck %s --check-prefix=PREFIX
// PREFIX: "-mllvm" "-x86-align-branch-prefix-size=5"
// RUN: %clang -target x86_64 -mpad-max-prefix-size=5 %s -c -### 2>&1 | FileCheck %s --check-prefix=PREFIX
// PREFIX: "-mllvm" "-x86-pad-max-prefix-size=5"
// RUN: %clang -target x86_64 -mbranches-within-32B-boundaries %s -c -### 2>&1 | FileCheck %s --check-prefix=32B
// 32B: "-mllvm" "-x86-branches-within-32B-boundaries"