Revert "[AArch64] Add support for -ffixed-x30"

[efriedma-quic]

This reverts commit e770153.

This wasn't reviewed, and the functionality in question was intentionally rejected the last time it was discussed in https://reviews.llvm.org/D56305 .

[llvmbot]

@llvm/pr-subscribers-clang
@llvm/pr-subscribers-clang-driver

@llvm/pr-subscribers-backend-aarch64

Author: Eli Friedman (efriedma-quic)

Changes

This reverts commit e770153.

This wasn't reviewed, and the functionality in question was intentionally rejected the last time it was discussed in https://reviews.llvm.org/D56305 .

---

Full diff: https://github.com/llvm/llvm-project/pull/88019.diff

4 Files Affected:

• (modified) clang/lib/Driver/ToolChains/Arch/AArch64.cpp (-3)
• (modified) clang/test/Driver/aarch64-fixed-x-register.c (-4)
• (modified) llvm/lib/Target/AArch64/AArch64.td (+1-1)
• (modified) llvm/test/CodeGen/AArch64/arm64-platform-reg.ll (+1-6)

diff --git a/clang/lib/Driver/ToolChains/Arch/AArch64.cpp b/clang/lib/Driver/ToolChains/Arch/AArch64.cpp
index 3e6e29584df3ac..2cd2b35ee51bc6 100644
--- a/clang/lib/Driver/ToolChains/Arch/AArch64.cpp
+++ b/clang/lib/Driver/ToolChains/Arch/AArch64.cpp
@@ -402,9 +402,6 @@ void aarch64::getAArch64TargetFeatures(const Driver &D,
   if (Args.hasArg(options::OPT_ffixed_x28))
     Features.push_back("+reserve-x28");
 
-  if (Args.hasArg(options::OPT_ffixed_x30))
-    Features.push_back("+reserve-x30");
-
   if (Args.hasArg(options::OPT_fcall_saved_x8))
     Features.push_back("+call-saved-x8");
 
diff --git a/clang/test/Driver/aarch64-fixed-x-register.c b/clang/test/Driver/aarch64-fixed-x-register.c
index 29024fde412543..7fc3e3e61105df 100644
--- a/clang/test/Driver/aarch64-fixed-x-register.c
+++ b/clang/test/Driver/aarch64-fixed-x-register.c
@@ -94,10 +94,6 @@
 // RUN: FileCheck --check-prefix=CHECK-FIXED-X28 < %t %s
 // CHECK-FIXED-X28: "-target-feature" "+reserve-x28"
 
-// RUN: %clang --target=aarch64-none-gnu -ffixed-x30 -### %s 2> %t
-// RUN: FileCheck --check-prefix=CHECK-FIXED-X30 < %t %s
-// CHECK-FIXED-X30: "-target-feature" "+reserve-x30"
-
 // Test multiple of reserve-x# options together.
 // RUN: %clang --target=aarch64-none-gnu \
 // RUN: -ffixed-x1 \
diff --git a/llvm/lib/Target/AArch64/AArch64.td b/llvm/lib/Target/AArch64/AArch64.td
index 3af427d526f80c..741c97a3dc009b 100644
--- a/llvm/lib/Target/AArch64/AArch64.td
+++ b/llvm/lib/Target/AArch64/AArch64.td
@@ -212,7 +212,7 @@ def FeatureStrictAlign : SubtargetFeature<"strict-align",
                                           "Disallow all unaligned memory "
                                           "access">;
 
-foreach i = {1-7,9-15,18,20-28,30} in
+foreach i = {1-7,9-15,18,20-28} in
     def FeatureReserveX#i : SubtargetFeature<"reserve-x"#i, "ReserveXRegister["#i#"]", "true",
                                              "Reserve X"#i#", making it unavailable "
                                              "as a GPR">;
diff --git a/llvm/test/CodeGen/AArch64/arm64-platform-reg.ll b/llvm/test/CodeGen/AArch64/arm64-platform-reg.ll
index c598306c2de301..3df2ef7aa59fc8 100644
--- a/llvm/test/CodeGen/AArch64/arm64-platform-reg.ll
+++ b/llvm/test/CodeGen/AArch64/arm64-platform-reg.ll
@@ -34,7 +34,6 @@
 ; RUN: llc -mtriple=arm64-linux-gnu -mattr=+reserve-x26 -o - %s | FileCheck %s --check-prefixes=CHECK-RESERVE,CHECK-RESERVE-X26
 ; RUN: llc -mtriple=arm64-linux-gnu -mattr=+reserve-x27 -o - %s | FileCheck %s --check-prefixes=CHECK-RESERVE,CHECK-RESERVE-X27
 ; RUN: llc -mtriple=arm64-linux-gnu -mattr=+reserve-x28 -o - %s | FileCheck %s --check-prefixes=CHECK-RESERVE,CHECK-RESERVE-X28
-; RUN: llc -mtriple=arm64-linux-gnu -mattr=+reserve-x30 -o - %s | FileCheck %s --check-prefixes=CHECK-RESERVE,CHECK-RESERVE-X30
 
 ; Test multiple of reserve-x# options together.
 ; RUN: llc -mtriple=arm64-linux-gnu \
@@ -73,7 +72,6 @@
 ; RUN: -mattr=+reserve-x26 \
 ; RUN: -mattr=+reserve-x27 \
 ; RUN: -mattr=+reserve-x28 \
-; RUN: -mattr=+reserve-x30 \
 ; RUN: -reserve-regs-for-regalloc=X8,X16,X17,X19 \
 ; RUN: -o - %s | FileCheck %s \
 ; RUN: --check-prefix=CHECK-RESERVE \
@@ -104,8 +102,7 @@
 ; RUN: --check-prefix=CHECK-RESERVE-X25 \
 ; RUN: --check-prefix=CHECK-RESERVE-X26 \
 ; RUN: --check-prefix=CHECK-RESERVE-X27 \
-; RUN: --check-prefix=CHECK-RESERVE-X28 \
-; RUN: --check-prefix=CHECK-RESERVE-X30
+; RUN: --check-prefix=CHECK-RESERVE-X28
 
 ; 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.
@@ -152,7 +149,6 @@ define void @keep_live() {
 ; CHECK-RESERVE-X26-NOT: ldr x26
 ; CHECK-RESERVE-X27-NOT: ldr x27
 ; CHECK-RESERVE-X28-NOT: ldr x28
-; CHECK-RESERVE-X30-NOT: ldr x30
 ; CHECK-RESERVE: Spill
 ; CHECK-RESERVE-NOT: ldr fp
 ; CHECK-RESERVE-X1-NOT: ldr x1,
@@ -182,7 +178,6 @@ define void @keep_live() {
 ; CHECK-RESERVE-X26-NOT: ldr x26
 ; CHECK-RESERVE-X27-NOT: ldr x27
 ; CHECK-RESERVE-X28-NOT: ldr x28
-; CHECK-RESERVE-X30-NOT: ldr x30
 ; CHECK-RESERVE: ret
   ret void
 }

[francisvm]

Makes sense, LGTM.

[aemerson]

@efriedma-quic @francisvm Can we restore this change? We need this for security hardening purposes to prevent LR allocated for general uses.

(There is also an issue with reserving LR in that AArch64's PEI doesn't add live-in flags for reserved regs, but I think we should fix that there once we restore this feature).

[efriedma-quic]

I'm not against having a security hardening feature to avoid using LR as a GPR. But we'd want to name it something different, to make it clear that it's a security-hardening feature, not a guarantee that the compiler won't clobber LR.

[aemerson]

Ok, given that our only way to implement something like this is with the reserving mechanism, I'll just rename the -ffixed-x30 to something like -mno-allocate-lr and keep the underlying cc1/target features the same?

[efriedma-quic]

We have a mechanism which specifically encodes the distinction we want here: ReserveXRegisterForRA. This was implemented for debugging/regression tests (see https://reviews.llvm.org/D132717), but we can expose it more generally.

Naming is hard, but maybe -mavoid-non-call-lr is better.

[aemerson]

Ah, perfect.

[aemerson]

Candidate PR: #98073