[PowerPC] Expand global named register support

[lei137]

Enable all valid registers for intrinsics that read from and write
to global named registers.

[llvmbot]

@llvm/pr-subscribers-backend-powerpc

Author: Lei Huang (lei137)

Changes

Enable all valid registers for intrinsics that read from and write
to global named registers.

---

Full diff: https://github.com/llvm/llvm-project/pull/112603.diff

4 Files Affected:

• (modified) llvm/lib/Target/PowerPC/PPCISelLowering.cpp (+17-13)
• (modified) llvm/test/CodeGen/PowerPC/named-reg-alloc-r0.ll (+4-5)
• (modified) llvm/test/CodeGen/PowerPC/named-reg-alloc-r2-64.ll (+1-2)
• (modified) llvm/test/CodeGen/PowerPC/named-reg-alloc-r2.ll (+1-2)

diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index cec1e507f08f2f..98b0a5ad4db0ee 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -17319,25 +17319,29 @@ SDValue PPCTargetLowering::LowerFRAMEADDR(SDValue Op,
   return FrameAddr;
 }
 
-// FIXME? Maybe this could be a TableGen attribute on some registers and
-// this table could be generated automatically from RegInfo.
+#define GET_REGISTER_MATCHER
+#include "PPCGenAsmMatcher.inc"
+
 Register PPCTargetLowering::getRegisterByName(const char* RegName, LLT VT,
                                               const MachineFunction &MF) const {
-  bool isPPC64 = Subtarget.isPPC64();
 
-  bool is64Bit = isPPC64 && VT == LLT::scalar(64);
-  if (!is64Bit && VT != LLT::scalar(32))
+  bool Is64Bit = Subtarget.isPPC64() && VT == LLT::scalar(64);
+  if (!Is64Bit && VT != LLT::scalar(32))
     report_fatal_error("Invalid register global variable type");
 
-  Register Reg = StringSwitch<Register>(RegName)
-                     .Case("r1", is64Bit ? PPC::X1 : PPC::R1)
-                     .Case("r2", isPPC64 ? Register() : PPC::R2)
-                     .Case("r13", (is64Bit ? PPC::X13 : PPC::R13))
-                     .Default(Register());
+  Register Reg = MatchRegisterName(RegName);
+  if (!Reg)
+    report_fatal_error(Twine("Invalid global name register \""
+                              + StringRef(RegName)  + "\"."));
+
+  // Convert GPR to GP8R register for 64bit.
+  if (Is64Bit && StringRef(RegName).starts_with_insensitive("r"))
+    Reg = Reg.id() - PPC::R0 + PPC::X0;
 
-  if (Reg)
-    return Reg;
-  report_fatal_error("Invalid register name global variable");
+  if (!Subtarget.getRegisterInfo()->getReservedRegs(MF).test(Reg))
+    report_fatal_error(Twine("Trying to obtain non-reservable register \"" +
+                             StringRef(RegName) + "\"."));
+  return Reg;
 }
 
 bool PPCTargetLowering::isAccessedAsGotIndirect(SDValue GA) const {
diff --git a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r0.ll b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r0.ll
index 11cb72296e2c43..be2fae8f3458be 100644
--- a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r0.ll
+++ b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r0.ll
@@ -1,11 +1,10 @@
-; RUN: not --crash llc < %s -mtriple=powerpc-unknown-linux-gnu 2>&1 | FileCheck %s
-; RUN: not --crash llc < %s -mtriple=powerpc-unknown-linux-gnu 2>&1 | FileCheck %s
-; RUN: not --crash llc < %s -mtriple=powerpc64-unknown-linux-gnu 2>&1 | FileCheck %s
+; RUN: not --crash llc -O0 < %s -mtriple=powerpc-unknown-linux-gnu 2>&1 | FileCheck %s
+; RUN: not --crash llc -O0 < %s -mtriple=powerpc-unknown-linux-gnu 2>&1 | FileCheck %s
+; RUN: not --crash llc -O0 < %s -mtriple=powerpc64-unknown-linux-gnu 2>&1 | FileCheck %s
 
 define i32 @get_reg() nounwind {
 entry:
-; FIXME: Include an allocatable-specific error message
-; CHECK: Invalid register name global variable
+; CHECK: Trying to obtain non-reservable register "r0".
         %reg = call i32 @llvm.read_register.i32(metadata !0)
   ret i32 %reg
 }
diff --git a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r2-64.ll b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r2-64.ll
index 3df778f445c733..b245c7d6f76c12 100644
--- a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r2-64.ll
+++ b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r2-64.ll
@@ -3,8 +3,7 @@
 
 define i64 @get_reg() nounwind {
 entry:
-; FIXME: Include an allocatable-specific error message
-; CHECK: Invalid register name global variable
+; CHECK: Trying to obtain non-reservable register "r2".
         %reg = call i64 @llvm.read_register.i64(metadata !0)
   ret i64 %reg
 }
diff --git a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r2.ll b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r2.ll
index ca79f857548ebe..ac79aa381ea7e0 100644
--- a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r2.ll
+++ b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r2.ll
@@ -3,8 +3,7 @@
 
 define i32 @get_reg() nounwind {
 entry:
-; FIXME: Include an allocatable-specific error message
-; CHECK-NOTPPC32: Invalid register name global variable
+; CHECK-NOTPPC32: Trying to obtain non-reservable register "r2".
         %reg = call i32 @llvm.read_register.i32(metadata !0)
   ret i32 %reg
 

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[redstar]

LGTM.

[nathanchance]

For what it's worth, this breaks building the Linux kernel for 32-bit powerpc for me because the kernel uses r2 as a global register variable for current.

$ make -skj"$(nproc)" ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- LLVM=1 LLVM_IAS=0 mrproper pmac32_defconfig ipc/namespace.o
fatal error: error in backend: Trying to obtain a reserved register "r2".
...

While this seems expected given the change, just in case, I ran this through cvise, which spits out:

register struct task_struct *current asm("r2");
struct task_struct {
  struct cred *cred;
};
struct cred {
  int euid;
} inc_ucount(int);
int *create_ipc_ns() {
  inc_ucount(({ ({ current->cred; })->euid; }));
  return (void *)8;
}

which works with clang immediately prior to this change and GCC:

$ clang --version | head -1
ClangBuiltLinux clang version 20.0.0git (https://github.com/llvm/llvm-project.git 06d192925d3510d0af6c10e6f64f6deabf66b75f)

$ clang --target=powerpc-linux-gnu -Wall -Werror -Wfatal-errors -c -o /dev/null namespace.i
fatal error: error in backend: Trying to obtain a reserved register "r2".
...

$ clang --version | head -1
ClangBuiltLinux clang version 20.0.0git (https://github.com/llvm/llvm-project.git e57548387000071562f44bfd66644480c8e6542d)

$ clang --target=powerpc-linux-gnu -Wall -Werror -Wfatal-errors -c -o /dev/null namespace.i

$ powerpc-linux-gcc --version | head -1
powerpc-linux-gcc (GCC) 14.2.0

$ powerpc-linux-gcc -O2 -Wall -Werror -Wfatal-errors -c -o /dev/null namespace.i

[lei137]

For what it's worth, this breaks building the Linux kernel for 32-bit powerpc for me because the kernel uses r2 as a global register variable for current.

$ make -skj"$(nproc)" ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- LLVM=1 LLVM_IAS=0 mrproper pmac32_defconfig ipc/namespace.o
fatal error: error in backend: Trying to obtain a reserved register "r2".
...

While this seems expected given the change, just in case, I ran this through cvise, which spits out:

register struct task_struct *current asm("r2");
struct task_struct {
  struct cred *cred;
};
struct cred {
  int euid;
} inc_ucount(int);
int *create_ipc_ns() {
  inc_ucount(({ ({ current->cred; })->euid; }));
  return (void *)8;
}

which works with clang immediately prior to this change and GCC:

$ clang --version | head -1
ClangBuiltLinux clang version 20.0.0git (https://github.com/llvm/llvm-project.git 06d192925d3510d0af6c10e6f64f6deabf66b75f)

$ clang --target=powerpc-linux-gnu -Wall -Werror -Wfatal-errors -c -o /dev/null namespace.i
fatal error: error in backend: Trying to obtain a reserved register "r2".
...

$ clang --version | head -1
ClangBuiltLinux clang version 20.0.0git (https://github.com/llvm/llvm-project.git e57548387000071562f44bfd66644480c8e6542d)

$ clang --target=powerpc-linux-gnu -Wall -Werror -Wfatal-errors -c -o /dev/null namespace.i

$ powerpc-linux-gcc --version | head -1
powerpc-linux-gcc (GCC) 14.2.0

$ powerpc-linux-gcc -O2 -Wall -Werror -Wfatal-errors -c -o /dev/null namespace.i

Thanks for reporting this. I will revert this change to unblock you and investigate further.

[lei137]

@nathanchance I took another look at the docs and there is no documented restrictions on what register can be used for this. I updated the patch to reflect what was originally there for r2. Can youn please give it a try?
#113482

Thanks!