[RISC-V] Add -msave-restore and -mno-save-restore to clang driver

Summary:
The GCC RISC-V toolchain accepts `-msave-restore` and `-mno-save-restore`
to control whether libcalls are used for saving and restoring the stack within
prologues and epilogues.

Clang currently errors if someone passes -msave-restore or -mno-save-restore.
This means that people need to change build configurations to use clang. This
patch adds these flags, so that clang invocations can now match gcc.

As the RISC-V backend does not currently have a `save-restore` target feature,
we emit a warning if someone requests `-msave-restore`. LLVM does not error if
we pass the (unimplemented) target features `+save-restore` or `-save-restore`.

Reviewers: asb, luismarques

Reviewed By: asb

Subscribers: rbar, johnrusso, simoncook, apazos, sabuasal, niosHD, kito-cheng, shiva0217, jrtc27, zzheng, edward-jones, rogfer01, MartinMosbeck, brucehoult, the_o, rkruppe, PkmX, jocewei, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D63498

llvm-svn: 364018

3 files changed, 27 insertions, 1 deletions

diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index bd51dbf953b..d766b856b0a 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -2130,6 +2130,10 @@ def mrelax : Flag<["-"], "mrelax">, Group<m_riscv_Features_Group>,
   HelpText<"Enable linker relaxation">;
 def mno_relax : Flag<["-"], "mno-relax">, Group<m_riscv_Features_Group>,
   HelpText<"Disable linker relaxation">;
+def msave_restore : Flag<["-"], "msave-restore">, Group<m_riscv_Features_Group>,
+  HelpText<"Enable using library calls for save and restore">;
+def mno_save_restore : Flag<["-"], "mno-save-restore">, Group<m_riscv_Features_Group>,
+  HelpText<"Disable using library calls for save and restore">;
 
 def munaligned_access : Flag<["-"], "munaligned-access">, Group<m_arm_Features_Group>,
   HelpText<"Allow memory accesses to be unaligned (AArch32/AArch64 only)">;
diff --git a/clang/lib/Driver/ToolChains/Arch/RISCV.cpp b/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
index e74fe13e2d4..075c951e82f 100644
--- a/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
+++ b/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
@@ -358,6 +358,16 @@ void riscv::getRISCVTargetFeatures(const Driver &D, const ArgList &Args,
   else
     Features.push_back("-relax");
 
+  // -mno-save-restore is default, unless -msave-restore is specified.
+  if (Args.hasFlag(options::OPT_msave_restore, options::OPT_mno_save_restore, false)) {
+    Features.push_back("+save-restore");
+    // ... but we don't yet support +save-restore, so issue a warning.
+    D.Diag(diag::warn_drv_clang_unsupported)
+      << Args.getLastArg(options::OPT_msave_restore)->getAsString(Args);
+  } else {
+    Features.push_back("-save-restore");
+  }
+
   // Now add any that the user explicitly requested on the command line,
   // which may override the defaults.
   handleTargetFeaturesGroup(Args, Features, options::OPT_m_riscv_Features_Group);
diff --git a/clang/test/Driver/riscv-features.c b/clang/test/Driver/riscv-features.c
index bdf9ef4084c..edd57c3a790 100644
--- a/clang/test/Driver/riscv-features.c
+++ b/clang/test/Driver/riscv-features.c
@@ -3,11 +3,23 @@
 
 // CHECK: fno-signed-char
 
+// RUN: %clang -target riscv32-unknown-elf -### %s 2>&1 | FileCheck %s -check-prefix=DEFAULT
+
 // RUN: %clang -target riscv32-unknown-elf -### %s -mrelax 2>&1 | FileCheck %s -check-prefix=RELAX
 // RUN: %clang -target riscv32-unknown-elf -### %s -mno-relax 2>&1 | FileCheck %s -check-prefix=NO-RELAX
-// RUN: %clang -target riscv32-unknown-elf -### %s 2>&1 | FileCheck %s -check-prefix=DEFAULT
 
 // RELAX: "-target-feature" "+relax"
 // NO-RELAX: "-target-feature" "-relax"
 // DEFAULT: "-target-feature" "+relax"
 // DEFAULT-NOT: "-target-feature" "-relax"
+
+// RUN: %clang -target riscv32-unknown-elf -### %s -msave-restore 2>&1 | FileCheck %s -check-prefix=SAVE-RESTORE
+// RUN: %clang -target riscv32-unknown-elf -### %s -mno-save-restore 2>&1 | FileCheck %s -check-prefix=NO-SAVE-RESTORE
+
+// SAVE-RESTORE: warning: the clang compiler does not support '-msave-restore'
+// DEFAULT-NOT: warning: the clang compiler does not support
+
+// SAVE-RESTORE: "-target-feature" "+save-restore"
+// NO-SAVE-RESTORE: "-target-feature" "-save-restore"
+// DEFAULT: "-target-feature" "-save-restore"
+// DEFAULT-NOT: "-target-feature" "+save-restore"
\ No newline at end of file