[RISCV] Reserve X18 by default for Android

[hiraditya]

Summary

Reserve X18 even when -fsanitize=shadow-call-stack is not enabled.

Based on: https://reviews.llvm.org/D143355

[phosek]

LGTM

[samitolvanen]

LGTM. Folding D145979 into this one might also make sense.

clang/test/Driver/riscv-fixed-x-register.c

343

This seems redundant. Isn't the LLVM codegen test sufficient here?

[asb]

clang/test/Driver/riscv-fixed-x-register.c

343

I think testing that the +reserve-x18 target feature is added by the frontend probably has some value.

I think it would better match the rest of this file to just do --check-prefix=CHECK-FIXED-X18 (I _think_ that works, but it is the end of the day so I may be missing something obvious...).

Please do try to remember to generate patches with full context (-U999999 or similar).

[asb]

LGTM.

[MaskRay]

clang/test/Driver/riscv-fixed-x-register.c

343

I prefer shared CHECK prefixes --check-prefix=CHECK-FIXED-X18 as well. We do that for many other tests.

343

/// Check that x18 is reserved on Android by default.

[hiraditya]

clang/test/Driver/riscv-fixed-x-register.c

343

@samitolvanen correct, this test isn't possible because llvm implicitly reserves the register so clang -cc1 never gets the "-target-feature" "+reserve-x18" parameter. I'll remove this test.

[hiraditya]

Folded D145979 here

clang/test/Driver/riscv-fixed-x-register.c

 // RUN: --check-prefix=CHECK-FIXED-X25 \
 // RUN: --check-prefix=CHECK-FIXED-X26 \
 // RUN: --check-prefix=CHECK-FIXED-X27 \
 // RUN: --check-prefix=CHECK-FIXED-X28 \
 // RUN: --check-prefix=CHECK-FIXED-X29 \
 // RUN: --check-prefix=CHECK-FIXED-X30 \
 // RUN: --check-prefix=CHECK-FIXED-X31 \
 // RUN: < %t %s
+
+// Check that x18 is reserved on Android by default
+// RUN: %clang --target=riscv64-linux-android -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-ANDROID-FIXED-X18 < %t %s
+// CHECK-ANDROID-FIXED-X18: "-target-feature" "+reserve-x18"

llvm/lib/TargetParser/RISCVTargetParser.cpp

   else
     Features.push_back("-64bit");
 
   return true;
 }
 
 bool isX18ReservedByDefault(const Triple &TT) {
   // X18 is reserved for the ShadowCallStack ABI (even when not enabled).
-  return TT.isOSFuchsia();
+  return TT.isOSFuchsia() || TT.isAndroid();
 }
 
 } // namespace RISCV
 } // namespace llvm

llvm/test/CodeGen/RISCV/reserved-regs.ll

 ; RUN: llc -mtriple=riscv32 -mattr=+reserve-x29 -verify-machineinstrs < %s | FileCheck %s -check-prefix=X29
 ; RUN: llc -mtriple=riscv64 -mattr=+reserve-x29 -verify-machineinstrs < %s | FileCheck %s -check-prefix=X29
 ; RUN: llc -mtriple=riscv32 -mattr=+reserve-x30 -verify-machineinstrs < %s | FileCheck %s -check-prefix=X30
 ; RUN: llc -mtriple=riscv64 -mattr=+reserve-x30 -verify-machineinstrs < %s | FileCheck %s -check-prefix=X30
 ; RUN: llc -mtriple=riscv32 -mattr=+reserve-x31 -verify-machineinstrs < %s | FileCheck %s -check-prefix=X31
 ; RUN: llc -mtriple=riscv64 -mattr=+reserve-x31 -verify-machineinstrs < %s | FileCheck %s -check-prefix=X31
 
 ; RUN: llc -mtriple=riscv64-fuchsia -verify-machineinstrs < %s | FileCheck %s -check-prefix=X18
+; RUN: llc -mtriple=riscv64-linux-android -verify-machineinstrs < %s | FileCheck %s -check-prefix=X18
 
 ; This program is free to use all registers, but needs a stack pointer for
 ; spill values, so do not test for reserving the stack pointer.
 
 ; Used to exhaust all registers
 @var = global [32 x i64] zeroinitializer
 
 define void @foo() {