[Driver][X86] Add an alias for -mpad-max-prefix-size

[skan]

Summary

LLVM does not have an option same as GAS's -malign-branch-prefix-size. GAS' s -malign-branch-prefix-size only elminates NOPs emitted by branch align, but clang's option -mpad-max-prefix-size aslo eliminates NOPs emitted by align directive. The two options are similar but slightly different.

My point is that we can make -malign-branch-prefix-size an alias for -mpad-max-prefix-size for user convenience when they need to prefix padding branches, but I am not sure whether it's appropriate. This revison is open mainly for discussion and I will not commit it if there is any objection.

[MaskRay]

Make -malign-branch-prefix-size an alias for -mpad-max-prefix-size (For GCC compatibility)

I cannot find a discussion on -mpad-max-prefix-size. Is it a planned GNU as option or GCC driver option?

[skan]

In D77728#1969788, @MaskRay wrote:

Make -malign-branch-prefix-size an alias for -mpad-max-prefix-size (For GCC compatibility)

I cannot find a discussion on -mpad-max-prefix-size. Is it a planned GNU as option or GCC driver option?

-mpad-max-prefix-size has nothing to do with GCC, it exposes the -x86-pad-max-prefix-size to clang

[MaskRay]

In D77728#1970912, @skan wrote:

In D77728#1969788, @MaskRay wrote:

Make -malign-branch-prefix-size an alias for -mpad-max-prefix-size (For GCC compatibility)

I cannot find a discussion on -mpad-max-prefix-size. Is it a planned GNU as option or GCC driver option?

-mpad-max-prefix-size has nothing to do with GCC, it exposes the -x86-pad-max-prefix-size to clang

Then it is incorrect to say HelpText<"Alias for -mpad-max-prefix-size">;// Alias for GCC compatibility

[skan]

In D77728#1970922, @MaskRay wrote:

In D77728#1970912, @skan wrote:

In D77728#1969788, @MaskRay wrote:

Make -malign-branch-prefix-size an alias for -mpad-max-prefix-size (For GCC compatibility)

I cannot find a discussion on -mpad-max-prefix-size. Is it a planned GNU as option or GCC driver option?

-mpad-max-prefix-size has nothing to do with GCC, it exposes the -x86-pad-max-prefix-size to clang

Then it is incorrect to say HelpText<"Alias for -mpad-max-prefix-size">;// Alias for GCC compatibility

Fine, we can have more discussion on this revision. D77628 really has nothing to do with GCC/GAS compatibility, could you remove the "request change"?

[skan]

Rebase

[skan]

Rebase(didn't rebase correctly last time)

[skan]

Fix the tests after rebase

[skan]

After careful consideration, I agree with @MaskRay ’s point of view that this alias is incorrect since they do different things. If there is no objection, I plan to abandon this revision.

clang/include/clang/Driver/Options.td

 def malign_loops_EQ : Joined<["-"], "malign-loops=">, Group<clang_ignored_m_Group>;
 def malign_jumps_EQ : Joined<["-"], "malign-jumps=">, Group<clang_ignored_m_Group>;
 def malign_branch_EQ : CommaJoined<["-"], "malign-branch=">, Group<m_Group>, Flags<[DriverOption]>,
   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 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 malign_branch_prefix_size_EQ : Joined<["-"], "malign-branch-prefix-size=">, Group<m_Group>, Flags<[DriverOption]>, Alias<mpad_max_prefix_size_EQ>,
+  HelpText<"Alias for -mpad-max-prefix-size">;// Alias for GCC compatibility
 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>;
 def mlong_calls : Flag<["-"], "mlong-calls">, Group<m_Group>,
   HelpText<"Generate branches with extended addressability, usually via indirect jumps.">;
 def mdouble_EQ : Joined<["-"], "mdouble=">, Group<m_Group>, Values<"32,64">, Flags<[CC1Option]>,
   HelpText<"Force double to be 32 bits or 64 bits">;
 def LongDouble_Group : OptionGroup<"<LongDouble group>">, Group<m_Group>,

clang/test/Driver/x86-malign-branch.c

 // TYPE-ERR: invalid argument 'bar' to -malign-branch=; each element must be one of: fused, jcc, jmp, call, ret, indirect
 
 /// 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 -malign-branch-prefix-size= for GCC compatibilty
+// RUN: %clang -target x86_64 -malign-branch-prefix-size=15 %s -c -### 2>&1 | FileCheck %s --check-prefix=PREFIX-15
+
 /// Test -mbranches-within-32B-boundaries
 // 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"
 
 /// 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 -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

clang/test/Driver/x86-malign-branch.s

 /// Test that -malign-branch* and -mbranches-within-32B-boundaries are handled for assembly files.
 
 // RUN: %clang -target x86_64 -malign-branch-boundary=16 %s -c -### 2>&1 | FileCheck %s --check-prefix=BOUNDARY
 // BOUNDARY: "-mllvm" "-x86-align-branch-boundary=16"
 
 // 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 -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 -malign-branch-prefix-size=5 %s -c -### 2>&1 | FileCheck %s --check-prefix=PREFIX
+
 // 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"