[llvm] [PowerPC] Expand global named register support (PR #112603)

Lei Huang via llvm-commits llvm-commits at lists.llvm.org
Tue Oct 22 11:33:22 PDT 2024


https://github.com/lei137 updated https://github.com/llvm/llvm-project/pull/112603

>From ae38254eeaf53b95f347c3657f61c271051bd978 Mon Sep 17 00:00:00 2001
From: Lei Huang <lei at ca.ibm.com>
Date: Tue, 8 Oct 2024 13:52:15 -0400
Subject: [PATCH 1/3] [PowerPC] Expand global named register support

Enable all valid registers for intrinsics that read from and write
to global named registers.
---
 llvm/lib/Target/PowerPC/PPCISelLowering.cpp   | 30 +++++++++++--------
 .../CodeGen/PowerPC/named-reg-alloc-r0.ll     |  9 +++---
 .../CodeGen/PowerPC/named-reg-alloc-r2-64.ll  |  3 +-
 .../CodeGen/PowerPC/named-reg-alloc-r2.ll     |  3 +-
 4 files changed, 23 insertions(+), 22 deletions(-)

diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 7199fac9b110b6..7e3c9df1d8d8e2 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -17367,25 +17367,29 @@ 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
 

>From 87a59ce91a81b7d588e4fcec6ff63e03fbed6d0c Mon Sep 17 00:00:00 2001
From: Lei Huang <lei at ca.ibm.com>
Date: Wed, 16 Oct 2024 15:43:31 -0400
Subject: [PATCH 2/3] Do not allow usage of reserved registers

---
 llvm/lib/Target/PowerPC/PPCISelLowering.cpp | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 7e3c9df1d8d8e2..0f935d2d94b615 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -17370,7 +17370,7 @@ SDValue PPCTargetLowering::LowerFRAMEADDR(SDValue Op,
 #define GET_REGISTER_MATCHER
 #include "PPCGenAsmMatcher.inc"
 
-Register PPCTargetLowering::getRegisterByName(const char* RegName, LLT VT,
+Register PPCTargetLowering::getRegisterByName(const char *RegName, LLT VT,
                                               const MachineFunction &MF) const {
 
   bool Is64Bit = Subtarget.isPPC64() && VT == LLT::scalar(64);
@@ -17379,15 +17379,15 @@ Register PPCTargetLowering::getRegisterByName(const char* RegName, LLT VT,
 
   Register Reg = MatchRegisterName(RegName);
   if (!Reg)
-    report_fatal_error(Twine("Invalid global name register \""
-                              + StringRef(RegName)  + "\"."));
+    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 (Subtarget.getRegisterInfo()->getReservedRegs(MF).test(Reg))
-    report_fatal_error(Twine("Trying to obtain non-reservable register \"" +
+    report_fatal_error(Twine("Trying to obtain a reserved register \"" +
                              StringRef(RegName) + "\"."));
   return Reg;
 }

>From 78536f120010cbfb7c19dad01211a004e84d11a0 Mon Sep 17 00:00:00 2001
From: Lei Huang <lei at ca.ibm.com>
Date: Fri, 18 Oct 2024 11:47:31 -0400
Subject: [PATCH 3/3] fix conditions and add tc to utilitze new supported
 registers

---
 llvm/lib/Target/PowerPC/PPCISelLowering.cpp   |   9 +-
 .../CodeGen/PowerPC/named-reg-alloc-r0.ll     |   3 +-
 .../CodeGen/PowerPC/named-reg-alloc-r1-64.ll  |   6 +-
 .../CodeGen/PowerPC/named-reg-alloc-r1.ll     |   9 +-
 .../CodeGen/PowerPC/named-reg-alloc-r13-64.ll |   7 +-
 .../CodeGen/PowerPC/named-reg-alloc-r13.ll    |   8 +-
 .../CodeGen/PowerPC/named-reg-alloc-r2-64.ll  |   3 +-
 .../CodeGen/PowerPC/named-reg-alloc-r2.ll     |   8 +-
 llvm/test/CodeGen/PowerPC/named-reg-alloc.ll  | 144 ++++++++++++++++++
 9 files changed, 167 insertions(+), 30 deletions(-)
 create mode 100644 llvm/test/CodeGen/PowerPC/named-reg-alloc.ll

diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 0f935d2d94b615..a4f0444ff2a645 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -17372,8 +17372,9 @@ SDValue PPCTargetLowering::LowerFRAMEADDR(SDValue Op,
 
 Register PPCTargetLowering::getRegisterByName(const char *RegName, LLT VT,
                                               const MachineFunction &MF) const {
+  bool IsPPC64 = Subtarget.isPPC64();
 
-  bool Is64Bit = Subtarget.isPPC64() && VT == LLT::scalar(64);
+  bool Is64Bit = IsPPC64 && VT == LLT::scalar(64);
   if (!Is64Bit && VT != LLT::scalar(32))
     report_fatal_error("Invalid register global variable type");
 
@@ -17382,6 +17383,12 @@ Register PPCTargetLowering::getRegisterByName(const char *RegName, LLT VT,
     report_fatal_error(
         Twine("Invalid global name register \"" + StringRef(RegName) + "\"."));
 
+  // FIXME: These registers are not flagged as reserved and we can generate
+  // code for `-O0` but not for `-O2`.  Need followup investigation as to why.
+  if ((IsPPC64 && Reg == PPC::R2) || Reg == PPC::R0)
+    report_fatal_error(Twine("Trying to reserve an invalid 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;
diff --git a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r0.ll b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r0.ll
index be2fae8f3458be..c6b9498a680f4d 100644
--- a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r0.ll
+++ b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r0.ll
@@ -1,10 +1,9 @@
 ; 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:
-; CHECK: Trying to obtain non-reservable register "r0".
+; CHECK: Trying to reserve an invalid register "r0".
         %reg = call i32 @llvm.read_register.i32(metadata !0)
   ret i32 %reg
 }
diff --git a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r1-64.ll b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r1-64.ll
index 080b1982c88cbf..96dbddd5bf1578 100644
--- a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r1-64.ll
+++ b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r1-64.ll
@@ -1,12 +1,10 @@
-; RUN: llc -verify-machineinstrs < %s -mtriple=powerpc64-unknown-linux-gnu 2>&1 | FileCheck %s
+; RUN: not --crash llc < %s -mtriple=powerpc64-unknown-linux-gnu 2>&1 | FileCheck %s
 
 define i64 @get_reg() nounwind {
+; CHECK: Trying to obtain a reserved register "r1".
 entry:
   %reg = call i64 @llvm.read_register.i64(metadata !0)
   ret i64 %reg
-
-; CHECK-LABEL: get_reg
-; CHECK: mr 3, 1
 }
 
 declare i64 @llvm.read_register.i64(metadata) nounwind
diff --git a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r1.ll b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r1.ll
index 6edd787e445e46..5980d09bc9c906 100644
--- a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r1.ll
+++ b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r1.ll
@@ -1,14 +1,11 @@
-; RUN: llc -verify-machineinstrs < %s -mtriple=powerpc-unknown-linux-gnu 2>&1 | FileCheck %s
-; RUN: llc -verify-machineinstrs < %s -mtriple=powerpc64-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
 
 define i32 @get_reg() nounwind {
+; CHECK: Trying to obtain a reserved register "r1".
 entry:
   %reg = call i32 @llvm.read_register.i32(metadata !0)
   ret i32 %reg
-
-; CHECK-LABEL: @get_reg
-; CHECK: mr 3, 1
-
 }
 
 declare i32 @llvm.read_register.i32(metadata) nounwind
diff --git a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r13-64.ll b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r13-64.ll
index 4d73fb3e81869c..8bd4d899f72609 100644
--- a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r13-64.ll
+++ b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r13-64.ll
@@ -1,13 +1,10 @@
-; RUN: llc -verify-machineinstrs < %s -mtriple=powerpc64-unknown-linux-gnu 2>&1 | FileCheck %s
+; RUN: not --crash llc < %s -mtriple=powerpc64-unknown-linux-gnu 2>&1 | FileCheck %s
 
 define i64 @get_reg() nounwind {
+; CHECK: Trying to obtain a reserved register "r13".
 entry:
   %reg = call i64 @llvm.read_register.i64(metadata !0)
   ret i64 %reg
-
-; CHECK-LABEL: @get_reg
-; CHECK: mr 3, 13
-
 }
 
 declare i64 @llvm.read_register.i64(metadata) nounwind
diff --git a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r13.ll b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r13.ll
index a7b778147980ac..2185a8a6cd5379 100644
--- a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r13.ll
+++ b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r13.ll
@@ -1,13 +1,11 @@
-; RUN: llc -verify-machineinstrs < %s -mtriple=powerpc-unknown-linux-gnu 2>&1 | FileCheck %s
-; RUN: llc -verify-machineinstrs < %s -mtriple=powerpc64-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
 
 define i32 @get_reg() nounwind {
+; CHECK: Trying to obtain a reserved register "r13".
 entry:
         %reg = call i32 @llvm.read_register.i32(metadata !0)
   ret i32 %reg
-
-; CHECK-LABEL: @get_reg
-; CHECK: mr 3, 13
 }
 
 declare i32 @llvm.read_register.i32(metadata) nounwind
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 b245c7d6f76c12..fdf7ea2711d827 100644
--- a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r2-64.ll
+++ b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r2-64.ll
@@ -1,9 +1,8 @@
 ; RUN: not --crash llc < %s -mtriple=powerpc64-unknown-linux-gnu 2>&1 | FileCheck %s
-; RUN: not --crash llc < %s -mtriple=powerpc64-unknown-linux-gnu 2>&1 | FileCheck %s
 
 define i64 @get_reg() nounwind {
 entry:
-; CHECK: Trying to obtain non-reservable register "r2".
+; CHECK: Trying to reserve an invalid 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 ac79aa381ea7e0..58c782901f3eb6 100644
--- a/llvm/test/CodeGen/PowerPC/named-reg-alloc-r2.ll
+++ b/llvm/test/CodeGen/PowerPC/named-reg-alloc-r2.ll
@@ -1,14 +1,12 @@
-; RUN: llc -verify-machineinstrs < %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 --check-prefix=CHECK-NOTPPC32
 
 define i32 @get_reg() nounwind {
 entry:
-; CHECK-NOTPPC32: Trying to obtain non-reservable register "r2".
+; CHECK-NOTPPC32: Trying to reserve an invalid register "r2".
+; CHECK: Trying to obtain a reserved register "r2".
         %reg = call i32 @llvm.read_register.i32(metadata !0)
   ret i32 %reg
-
-; CHECK-LABEL: @get_reg
-; CHECK: mr 3, 2
 }
 
 declare i32 @llvm.read_register.i32(metadata) nounwind
diff --git a/llvm/test/CodeGen/PowerPC/named-reg-alloc.ll b/llvm/test/CodeGen/PowerPC/named-reg-alloc.ll
new file mode 100644
index 00000000000000..38d22475ead910
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/named-reg-alloc.ll
@@ -0,0 +1,144 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -O0 -verify-machineinstrs < %s -mtriple=powerpc-unknown-linux-gnu 2>&1 | FileCheck %s
+; RUN: llc -O0 -verify-machineinstrs < %s -mtriple=powerpc64-unknown-linux-gnu 2>&1 | FileCheck %s --check-prefix=CHECK64
+
+ at mVal = dso_local global i32 15, align 4
+ at myGVal = dso_local global i32 0, align 4
+
+define dso_local void @testSetIntReg(i32 noundef signext %xx) {
+; CHECK-LABEL: testSetIntReg:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    mr 5, 3
+; CHECK-NEXT:    blr
+;
+; CHECK64-LABEL: testSetIntReg:
+; CHECK64:       # %bb.0: # %entry
+; CHECK64-NEXT:    mr 5, 3
+; CHECK64-NEXT:    blr
+entry:
+  tail call void @llvm.write_register.i32(metadata !0, i32 %xx)
+  ret void
+}
+
+declare void @llvm.write_register.i32(metadata, i32)
+
+define dso_local signext range(i32 0, 2) i32 @testCmpReg() {
+; CHECK-LABEL: testCmpReg:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    lis 3, mVal at ha
+; CHECK-NEXT:    lwz 3, mVal at l(3)
+; CHECK-NEXT:    xori 3, 3, 15
+; CHECK-NEXT:    cntlzw 3, 3
+; CHECK-NEXT:    srwi 3, 3, 5
+; CHECK-NEXT:    blr
+;
+; CHECK64-LABEL: testCmpReg:
+; CHECK64:       # %bb.0: # %entry
+; CHECK64-NEXT:    addis 3, 2, mVal at toc@ha
+; CHECK64-NEXT:    addi 3, 3, mVal at toc@l
+; CHECK64-NEXT:    lwz 3, 0(3)
+; CHECK64-NEXT:    xori 3, 3, 15
+; CHECK64-NEXT:    cntlzw 3, 3
+; CHECK64-NEXT:    srwi 3, 3, 5
+; CHECK64-NEXT:    extsw 3, 3
+; CHECK64-NEXT:    blr
+entry:
+  tail call void @llvm.write_register.i32(metadata !0, i32 15)
+  %0 = load i32, ptr @mVal, align 4
+  %1 = tail call i32 @llvm.read_register.i32(metadata !0)
+  %cmp = icmp eq i32 %0, %1
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
+
+declare i32 @llvm.read_register.i32(metadata)
+
+define dso_local void @testSetIntReg2(i32 noundef signext %xx) {
+; CHECK-LABEL: testSetIntReg2:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    stwu 1, -48(1)
+; CHECK-NEXT:    .cfi_def_cfa_offset 48
+; CHECK-NEXT:    .cfi_offset r23, -36
+; CHECK-NEXT:    stw 23, 12(1) # 4-byte Folded Spill
+; CHECK-NEXT:    mr 23, 3
+; CHECK-NEXT:    lwz 23, 12(1) # 4-byte Folded Reload
+; CHECK-NEXT:    addi 1, 1, 48
+; CHECK-NEXT:    blr
+;
+; CHECK64-LABEL: testSetIntReg2:
+; CHECK64:       # %bb.0: # %entry
+; CHECK64-NEXT:    std 23, -72(1) # 8-byte Folded Spill
+; CHECK64-NEXT:    mr 23, 3
+; CHECK64-NEXT:    ld 23, -72(1) # 8-byte Folded Reload
+; CHECK64-NEXT:    blr
+entry:
+  tail call void @llvm.write_register.i32(metadata !1, i32 %xx)
+  ret void
+}
+
+define dso_local signext i32 @testReturnReg() {
+; CHECK-LABEL: testReturnReg:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    stwu 1, -48(1)
+; CHECK-NEXT:    .cfi_def_cfa_offset 48
+; CHECK-NEXT:    .cfi_offset r23, -36
+; CHECK-NEXT:    stw 23, 12(1) # 4-byte Folded Spill
+; CHECK-NEXT:    li 23, 125
+; CHECK-NEXT:    mr 3, 23
+; CHECK-NEXT:    lwz 23, 12(1) # 4-byte Folded Reload
+; CHECK-NEXT:    addi 1, 1, 48
+; CHECK-NEXT:    blr
+;
+; CHECK64-LABEL: testReturnReg:
+; CHECK64:       # %bb.0: # %entry
+; CHECK64-NEXT:    std 23, -72(1) # 8-byte Folded Spill
+; CHECK64-NEXT:    li 23, 125
+; CHECK64-NEXT:    extsw 3, 23
+; CHECK64-NEXT:    ld 23, -72(1) # 8-byte Folded Reload
+; CHECK64-NEXT:    blr
+entry:
+  tail call void @llvm.write_register.i32(metadata !1, i32 125)
+  %0 = tail call i32 @llvm.read_register.i32(metadata !1)
+  ret i32 %0
+}
+
+define dso_local void @testViaASM(i32 noundef signext %xx) {
+; CHECK-LABEL: testViaASM:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    stwu 1, -64(1)
+; CHECK-NEXT:    .cfi_def_cfa_offset 64
+; CHECK-NEXT:    .cfi_offset r20, -48
+; CHECK-NEXT:    stw 20, 16(1) # 4-byte Folded Spill
+; CHECK-NEXT:    mr 20, 3
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    addi 3, 1, 1
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:    lis 4, myGVal at ha
+; CHECK-NEXT:    stw 3, myGVal at l(4)
+; CHECK-NEXT:    lwz 20, 16(1) # 4-byte Folded Reload
+; CHECK-NEXT:    addi 1, 1, 64
+; CHECK-NEXT:    blr
+;
+; CHECK64-LABEL: testViaASM:
+; CHECK64:       # %bb.0: # %entry
+; CHECK64-NEXT:    std 20, -96(1) # 8-byte Folded Spill
+; CHECK64-NEXT:    mr 20, 3
+; CHECK64-NEXT:    #APP
+; CHECK64-NEXT:    addi 3, 1, 1
+; CHECK64-NEXT:    #NO_APP
+; CHECK64-NEXT:    addis 4, 2, myGVal at toc@ha
+; CHECK64-NEXT:    addi 4, 4, myGVal at toc@l
+; CHECK64-NEXT:    stw 3, 0(4)
+; CHECK64-NEXT:    ld 20, -96(1) # 8-byte Folded Reload
+; CHECK64-NEXT:    blr
+entry:
+  tail call void @llvm.write_register.i32(metadata !2, i32 %xx)
+  %0 = tail call i32 @llvm.read_register.i32(metadata !2)
+  %1 = tail call i32 asm "addi $0, $2, $2", "=r,{r20},K"(i32 %0, i32 1)
+  store i32 %1, ptr @myGVal, align 4
+  ret void
+}
+
+!0 = !{!"r5"}
+!1 = !{!"r23"}
+!2 = !{!"r20"}



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