[AArch64] Support reserving arbitrary general purpose registers

[phosek]

Summary

This is a follow up to D48580 and D48581 which allows reserving
arbitrary general purpose registers with the exception of registers
with special purpose (X8, X16-X18, X29, X30) and registers used by LLVM
(X0, X19). This change also generalizes some of the existing logic to
rely entirely on values generated from tablegen.

[trong]

clang/include/clang/Driver/Options.td

2121 ↗

(On Diff #180251)

With this patch x9-15 can be specified as both reserved and callee-saved. Could you extend test/CodeGen/AArch64/arm64-reserve-call-saved-reg.ll as well?

clang/lib/Driver/ToolChains/Arch/AArch64.cpp

318 ↗

(On Diff #180251)

What happens (should happen) if we reserve x0 and compile a function with a return value?

[carwil]

Hi, we're currently working on similar functionality for the ARM backend, so I got pointed to take a look at this patch.
Looks good to me, I quite like the tablegen improvements, but agree with trong's comments.

I assume you've omitted X19, as LLVM uses it as the base pointer?

[phosek]

In D56305#1363417, @carwil wrote:

Hi, we're currently working on similar functionality for the ARM backend, so I got pointed to take a look at this patch.
Looks good to me, I quite like the tablegen improvements, but agree with trong's comments.

Done.

I assume you've omitted X19, as LLVM uses it as the base pointer?

Yes.

clang/lib/Driver/ToolChains/Arch/AArch64.cpp

318 ↗

(On Diff #180251)

Clang throws error: AArch64 doesn't support function calls if any of the argument registers is reserved. as for any other argument register.

[trong]

clang/lib/Driver/ToolChains/Arch/AArch64.cpp

318 ↗

(On Diff #180251)

Yes, if x0 is reserved, it can't be used to pass arguments. But what happens if x0 is used to return a value? For example:

int foo() {
    return 1;
}

It would be helpful if compiling foo() with x0 reserved threw an error.

[trong]

clang/lib/Driver/ToolChains/Arch/AArch64.cpp

318 ↗

(On Diff #180251)

OTOH, gcc doesn't complain, so maybe we're OK here.

[efriedma]

clang/lib/Driver/ToolChains/Arch/AArch64.cpp

318 ↗

(On Diff #180251)

IIRC gcc never reports any errors for its version of these flags; that doesn't mean we should accept constructs which don't have defined behavior. I'd prefer to print an error in any situation where we would implicitly use a reserved register.

[phosek]

clang/lib/Driver/ToolChains/Arch/AArch64.cpp

318 ↗

(On Diff #180251)

I've looked into it, but there are several places where LLVM assumes and uses x0, so I think it's safer for now to disallow reserving x0 just like we do with x19.

include/clang/Driver/Options.td

 def mgeneral_regs_only : Flag<["-"], "mgeneral-regs-only">, Group<m_aarch64_Features_Group>,
   HelpText<"Generate code which only uses the general purpose registers (AArch64 only)">;
 def mfix_cortex_a53_835769 : Flag<["-"], "mfix-cortex-a53-835769">,
   Group<m_aarch64_Features_Group>,
   HelpText<"Workaround Cortex-A53 erratum 835769 (AArch64 only)">;
 def mno_fix_cortex_a53_835769 : Flag<["-"], "mno-fix-cortex-a53-835769">,
   Group<m_aarch64_Features_Group>,
   HelpText<"Don't workaround Cortex-A53 erratum 835769 (AArch64 only)">;
-foreach i = {1-7,18,20} in
+foreach i = {1-7,9-15,18,20-28} in
   def ffixed_x#i : Flag<["-"], "ffixed-x"#i>, Group<m_aarch64_Features_Group>,
     HelpText<"Reserve the "#i#" register (AArch64 only)">;
 
 foreach i = {8-15,18} in
   def fcall_saved_x#i : Flag<["-"], "fcall-saved-x"#i>, Group<m_aarch64_Features_Group>,
     HelpText<"Make the x"#i#" register call-saved (AArch64 only)">;
 
 def msign_return_address_EQ : Joined<["-"], "msign-return-address=">,

lib/Driver/ToolChains/Arch/AArch64.cpp

if (Args.hasArg(options::OPT_ffixed_x5))
     Features.push_back("+reserve-x5");
 
   if (Args.hasArg(options::OPT_ffixed_x6))
     Features.push_back("+reserve-x6");
 
   if (Args.hasArg(options::OPT_ffixed_x7))
     Features.push_back("+reserve-x7");
 
+  if (Args.hasArg(options::OPT_ffixed_x9))
+    Features.push_back("+reserve-x9");
+
+  if (Args.hasArg(options::OPT_ffixed_x10))
+    Features.push_back("+reserve-x10");
+
+  if (Args.hasArg(options::OPT_ffixed_x11))
+    Features.push_back("+reserve-x11");
+
+  if (Args.hasArg(options::OPT_ffixed_x12))
+    Features.push_back("+reserve-x12");
+
+  if (Args.hasArg(options::OPT_ffixed_x13))
+    Features.push_back("+reserve-x13");
+
+  if (Args.hasArg(options::OPT_ffixed_x14))
+    Features.push_back("+reserve-x14");
+
+  if (Args.hasArg(options::OPT_ffixed_x15))
+    Features.push_back("+reserve-x15");
+
   if (Args.hasArg(options::OPT_ffixed_x18))
     Features.push_back("+reserve-x18");
 
   if (Args.hasArg(options::OPT_ffixed_x20))
     Features.push_back("+reserve-x20");
 
+  if (Args.hasArg(options::OPT_ffixed_x21))
+    Features.push_back("+reserve-x21");
+
+  if (Args.hasArg(options::OPT_ffixed_x22))
+    Features.push_back("+reserve-x22");
+
+  if (Args.hasArg(options::OPT_ffixed_x23))
+    Features.push_back("+reserve-x23");
+
+  if (Args.hasArg(options::OPT_ffixed_x24))
+    Features.push_back("+reserve-x24");
+
+  if (Args.hasArg(options::OPT_ffixed_x26))
+    Features.push_back("+reserve-x26");
+
+  if (Args.hasArg(options::OPT_ffixed_x27))
+    Features.push_back("+reserve-x27");
+
+  if (Args.hasArg(options::OPT_ffixed_x28))
+    Features.push_back("+reserve-x28");
+
   if (Args.hasArg(options::OPT_fcall_saved_x8))
     Features.push_back("+call-saved-x8");
 
   if (Args.hasArg(options::OPT_fcall_saved_x9))
     Features.push_back("+call-saved-x9");
 
   if (Args.hasArg(options::OPT_fcall_saved_x10))
     Features.push_back("+call-saved-x10");

test/Driver/aarch64-fixed-x-register.c

 // RUN: %clang -target aarch64-none-gnu -ffixed-x6 -### %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-FIXED-X6 < %t %s
 // CHECK-FIXED-X6: "-target-feature" "+reserve-x6"
 
 // RUN: %clang -target aarch64-none-gnu -ffixed-x7 -### %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-FIXED-X7 < %t %s
 // CHECK-FIXED-X7: "-target-feature" "+reserve-x7"
 
+// RUN: %clang -target aarch64-none-gnu -ffixed-x9 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X9 < %t %s
+// CHECK-FIXED-X9: "-target-feature" "+reserve-x9"
+
+// RUN: %clang -target aarch64-none-gnu -ffixed-x10 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X10 < %t %s
+// CHECK-FIXED-X10: "-target-feature" "+reserve-x10"
+
+// RUN: %clang -target aarch64-none-gnu -ffixed-x11 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X11 < %t %s
+// CHECK-FIXED-X11: "-target-feature" "+reserve-x11"
+
+// RUN: %clang -target aarch64-none-gnu -ffixed-x12 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X12 < %t %s
+// CHECK-FIXED-X12: "-target-feature" "+reserve-x12"
+
+// RUN: %clang -target aarch64-none-gnu -ffixed-x13 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X13 < %t %s
+// CHECK-FIXED-X13: "-target-feature" "+reserve-x13"
+
+// RUN: %clang -target aarch64-none-gnu -ffixed-x14 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X14 < %t %s
+// CHECK-FIXED-X14: "-target-feature" "+reserve-x14"
+
+// RUN: %clang -target aarch64-none-gnu -ffixed-x15 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X15 < %t %s
+// CHECK-FIXED-X15: "-target-feature" "+reserve-x15"
+
 // RUN: %clang -target aarch64-none-gnu -ffixed-x18 -### %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-FIXED-X18 < %t %s
 // CHECK-FIXED-X18: "-target-feature" "+reserve-x18"
 
 // RUN: %clang -target aarch64-none-gnu -ffixed-x20 -### %s 2> %t
 // RUN: FileCheck --check-prefix=CHECK-FIXED-X20 < %t %s
 // CHECK-FIXED-X20: "-target-feature" "+reserve-x20"
 
+// RUN: %clang -target aarch64-none-gnu -ffixed-x21 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X21 < %t %s
+// CHECK-FIXED-X21: "-target-feature" "+reserve-x21"
+
+// RUN: %clang -target aarch64-none-gnu -ffixed-x22 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X22 < %t %s
+// CHECK-FIXED-X22: "-target-feature" "+reserve-x22"
+
+// RUN: %clang -target aarch64-none-gnu -ffixed-x23 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X23 < %t %s
+// CHECK-FIXED-X23: "-target-feature" "+reserve-x23"
+
+// RUN: %clang -target aarch64-none-gnu -ffixed-x24 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X24 < %t %s
+// CHECK-FIXED-X24: "-target-feature" "+reserve-x24"
+
+// RUN: %clang -target aarch64-none-gnu -ffixed-x25 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X25 < %t %s
+// CHECK-FIXED-X25: "-target-feature" "+reserve-x25"
+
+// RUN: %clang -target aarch64-none-gnu -ffixed-x26 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X26 < %t %s
+// CHECK-FIXED-X26: "-target-feature" "+reserve-x26"
+
+// RUN: %clang -target aarch64-none-gnu -ffixed-x27 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X27 < %t %s
+// CHECK-FIXED-X27: "-target-feature" "+reserve-x27"
+
+// RUN: %clang -target aarch64-none-gnu -ffixed-x28 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-FIXED-X28 < %t %s
+// CHECK-FIXED-X28: "-target-feature" "+reserve-x28"
+
 // Test multiple of reserve-x# options together.
 // RUN: %clang -target aarch64-none-gnu \
 // RUN: -ffixed-x1 \
 // RUN: -ffixed-x2 \
 // RUN: -ffixed-x18 \
 // RUN: -### %s 2> %t
 // RUN: FileCheck \
 // RUN: --check-prefix=CHECK-FIXED-X1 \
 // RUN: --check-prefix=CHECK-FIXED-X2 \
 // RUN: --check-prefix=CHECK-FIXED-X18 \
 // RUN: < %t %s
 
 // Test all reserve-x# options together.
 // RUN: %clang -target aarch64-none-gnu \
 // RUN: -ffixed-x1 \
 // RUN: -ffixed-x2 \
 // RUN: -ffixed-x3 \
 // RUN: -ffixed-x4 \
 // RUN: -ffixed-x5 \
 // RUN: -ffixed-x6 \
 // RUN: -ffixed-x7 \
+// RUN: -ffixed-x9 \
+// RUN: -ffixed-x10 \
+// RUN: -ffixed-x11 \
+// RUN: -ffixed-x12 \
+// RUN: -ffixed-x13 \
+// RUN: -ffixed-x14 \
+// RUN: -ffixed-x15 \
 // RUN: -ffixed-x18 \
 // RUN: -ffixed-x20 \
+// RUN: -ffixed-x21 \
+// RUN: -ffixed-x22 \
+// RUN: -ffixed-x23 \
+// RUN: -ffixed-x24 \
+// RUN: -ffixed-x25 \
+// RUN: -ffixed-x26 \
+// RUN: -ffixed-x27 \
+// RUN: -ffixed-x28 \
 // RUN: -### %s 2> %t
 // RUN: FileCheck \
 // RUN: --check-prefix=CHECK-FIXED-X1 \
 // RUN: --check-prefix=CHECK-FIXED-X2 \
 // RUN: --check-prefix=CHECK-FIXED-X3 \
 // RUN: --check-prefix=CHECK-FIXED-X4 \
 // RUN: --check-prefix=CHECK-FIXED-X5 \
 // RUN: --check-prefix=CHECK-FIXED-X6 \
 // RUN: --check-prefix=CHECK-FIXED-X7 \
+// RUN: --check-prefix=CHECK-FIXED-X9 \
+// RUN: --check-prefix=CHECK-FIXED-X10 \
+// RUN: --check-prefix=CHECK-FIXED-X11 \
+// RUN: --check-prefix=CHECK-FIXED-X12 \
+// RUN: --check-prefix=CHECK-FIXED-X13 \
+// RUN: --check-prefix=CHECK-FIXED-X14 \
+// RUN: --check-prefix=CHECK-FIXED-X15 \
 // RUN: --check-prefix=CHECK-FIXED-X18 \
 // RUN: --check-prefix=CHECK-FIXED-X20 \
+// RUN: --check-prefix=CHECK-FIXED-X21 \
+// RUN: --check-prefix=CHECK-FIXED-X22 \
+// RUN: --check-prefix=CHECK-FIXED-X23 \
+// RUN: --check-prefix=CHECK-FIXED-X24 \
+// 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: < %t %s