[COFF, ARM64] Reserve X18 register by default

[mstorsjo]

lib/Target/AArch64/AArch64Subtarget.cpp

176

The TT.isOSBinFormatCOFF() part feels a little superfluous here

test/CodeGen/AArch64/arm64-platform-reg.ll

1

Unrelated to this particular patch, but shouldn't we drop the -mattr=+reserve-x18 here, to also test that darwin actuall does this right by default? (I'm not sure if there's any other tests that explicitly test that?)

28

Why the custom test prefix for windows/coff? Doesn't the existing CHECK-RESERVE-X18 also work for aarch64-windows?

[mgrang]

lib/Target/AArch64/AArch64Subtarget.cpp

176

True. It can be removed.

test/CodeGen/AArch64/arm64-platform-reg.ll

1

I thought so too. Will fix this in another patch.

28

I wasn't sure about the "ldr fp" and "Spill". Is fp an alias for x18?

[mstorsjo]

test/CodeGen/AArch64/arm64-platform-reg.ll

28

fp is an alias for x29; I think that part of the test just makes sure that nothing tries to use that register for the copying that the test does (especially when x18 isn't available), since that register shouldn't be used for unrelated things.

[mgrang]

Removed isOSBinFormatCOFF().
Removed extra check label CHECK-RESERVE-X18-COFF.

lib/Target/AArch64/AArch64Subtarget.cpp

 };
 
 } // end anonymous namespace
 #endif
 
 AArch64Subtarget::AArch64Subtarget(const Triple &TT, const std::string &CPU,
                                    const std::string &FS,
                                    const TargetMachine &TM, bool LittleEndian)
-    : AArch64GenSubtargetInfo(TT, CPU, FS), ReserveX18(TT.isOSDarwin()),
+    : AArch64GenSubtargetInfo(TT, CPU, FS),
+      ReserveX18(TT.isOSDarwin() || TT.isOSWindows()),
       IsLittle(LittleEndian), TargetTriple(TT), FrameLowering(),
       InstrInfo(initializeSubtargetDependencies(FS, CPU)), TSInfo(),
       TLInfo(TM, *this), GISel() {
 #ifndef LLVM_BUILD_GLOBAL_ISEL
   GISelAccessor *AArch64GISel = new GISelAccessor();
 #else
   AArch64GISelActualAccessor *AArch64GISel = new AArch64GISelActualAccessor();
   AArch64GISel->CallLoweringInfo.reset(
       new AArch64CallLowering(*getTargetLowering()));

test/CodeGen/AArch64/arm64-platform-reg.ll

 ; RUN: llc -mtriple=arm64-apple-ios -mattr=+reserve-x18 -o - %s | FileCheck %s --check-prefix=CHECK-RESERVE-X18
 ; RUN: llc -mtriple=arm64-freebsd-gnu -mattr=+reserve-x18 -o - %s | FileCheck %s --check-prefix=CHECK-RESERVE-X18
 ; RUN: llc -mtriple=arm64-linux-gnu -o - %s | FileCheck %s
+; RUN: llc -mtriple=aarch64-windows -o - %s | FileCheck %s --check-prefix=CHECK-RESERVE-X18
 
 ; x18 is reserved as a platform register on Darwin but not on other
 ; systems. Create loads of register pressure and make sure this is respected.
 
 ; Also, fp must always refer to a valid frame record, even if it's not the one
 ; of the current function, so it shouldn't be used either.
 
 @var = global [30 x i64] zeroinitializer
 
 define void @keep_live() {
   %val = load volatile [30 x i64], [30 x i64]* @var
   store volatile [30 x i64] %val, [30 x i64]* @var
 
 ; CHECK: ldr x18
 ; CHECK: str x18
 
 ; CHECK-RESERVE-X18-NOT: ldr fp
 ; CHECK-RESERVE-X18-NOT: ldr x18
 ; CHECK-RESERVE-X18: Spill
 ; CHECK-RESERVE-X18-NOT: ldr fp
 ; CHECK-RESERVE-X18-NOT: ldr x18
 ; CHECK-RESERVE-X18: ret
   ret void
 }