[RISCV] Avoid using x7/t2 for indirect branches which need landing pad. (#68292)

When Zicfilp enabled, this avoids selecting indirect jumps to PseudoBRIND/PseudoCALLIndirect/PseudoTAILIndirect, since they may uses X7 as rs1 and be identified as a software guarded jump. There is an another PR #66762 to use software guarded jump for jumptable branch.

Author: yetingk

llvm/lib/Target/RISCV/GISel/RISCVRegisterBankInfo.cpp

@@ -117,7 +117,9 @@ RISCVRegisterBankInfo::getRegBankFromRegClass(const TargetRegisterClass &RC,
   case RISCV::GPRNoX0RegClassID:
   case RISCV::GPRNoX0X2RegClassID:
   case RISCV::GPRJALRRegClassID:
+  case RISCV::GPRJALRNonX7RegClassID:
   case RISCV::GPRTCRegClassID:
+  case RISCV::GPRTCNonX7RegClassID:
   case RISCV::GPRC_and_GPRTCRegClassID:
   case RISCV::GPRCRegClassID:
   case RISCV::GPRC_and_SR07RegClassID:

llvm/lib/Target/RISCV/RISCVFeatures.td

@@ -156,6 +156,8 @@ def FeatureStdExtZicfilp
 def HasStdExtZicfilp : Predicate<"Subtarget->hasStdExtZicfilp()">,
                        AssemblerPredicate<(all_of FeatureStdExtZicfilp),
                                           "'Zicfilp' (Landing pad)">;
+def NoStdExtZicfilp : Predicate<"!Subtarget->hasStdExtZicfilp()">,
+                                 AssemblerPredicate<(all_of (not FeatureStdExtZicfilp))>;
 
 def FeatureStdExtZicfiss
     : RISCVExperimentalExtension<"zicfiss", 0, 4,

llvm/lib/Target/RISCV/RISCVInstrInfo.td

@@ -1448,13 +1448,29 @@ let isBarrier = 1, isBranch = 1, isTerminator = 1 in
 def PseudoBR : Pseudo<(outs), (ins simm21_lsb0_jal:$imm20), [(br bb:$imm20)]>,
                PseudoInstExpansion<(JAL X0, simm21_lsb0_jal:$imm20)>;
 
-let isBarrier = 1, isBranch = 1, isIndirectBranch = 1, isTerminator = 1 in
+let Predicates = [NoStdExtZicfilp],
+    isBarrier = 1, isBranch = 1, isIndirectBranch = 1, isTerminator = 1 in
 def PseudoBRIND : Pseudo<(outs), (ins GPRJALR:$rs1, simm12:$imm12), []>,
                   PseudoInstExpansion<(JALR X0, GPR:$rs1, simm12:$imm12)>;
 
+let Predicates = [HasStdExtZicfilp],
+    isBarrier = 1, isBranch = 1, isIndirectBranch = 1, isTerminator = 1 in
+def PseudoBRINDNonX7 : Pseudo<(outs), (ins GPRJALRNonX7:$rs1, simm12:$imm12), []>,
+                       PseudoInstExpansion<(JALR X0, GPR:$rs1, simm12:$imm12)>;
+
+// For Zicfilp, need to avoid using X7/T2 for indirect branches which need
+// landing pad.
+let Predicates = [HasStdExtZicfilp] in {
+def : Pat<(brind GPRJALRNonX7:$rs1), (PseudoBRINDNonX7 GPRJALRNonX7:$rs1, 0)>;
+def : Pat<(brind (add GPRJALRNonX7:$rs1, simm12:$imm12)),
+          (PseudoBRINDNonX7 GPRJALRNonX7:$rs1, simm12:$imm12)>;
+}
+
+let Predicates = [NoStdExtZicfilp] in {
 def : Pat<(brind GPRJALR:$rs1), (PseudoBRIND GPRJALR:$rs1, 0)>;
 def : Pat<(brind (add GPRJALR:$rs1, simm12:$imm12)),
           (PseudoBRIND GPRJALR:$rs1, simm12:$imm12)>;
+}
 
 // PseudoCALLReg is a generic pseudo instruction for calls which will eventually
 // expand to auipc and jalr while encoding, with any given register used as the
@@ -1484,10 +1500,16 @@ def : Pat<(riscv_call texternalsym:$func), (PseudoCALL texternalsym:$func)>;
 def : Pat<(riscv_sret_glue), (SRET (XLenVT X0), (XLenVT X0))>;
 def : Pat<(riscv_mret_glue), (MRET (XLenVT X0), (XLenVT X0))>;
 
-let isCall = 1, Defs = [X1] in
+let isCall = 1, Defs = [X1] in {
+let Predicates = [NoStdExtZicfilp] in
 def PseudoCALLIndirect : Pseudo<(outs), (ins GPRJALR:$rs1),
                                 [(riscv_call GPRJALR:$rs1)]>,
                          PseudoInstExpansion<(JALR X1, GPR:$rs1, 0)>;
+let Predicates = [HasStdExtZicfilp] in
+def PseudoCALLIndirectNonX7 : Pseudo<(outs), (ins GPRJALRNonX7:$rs1),
+                                     [(riscv_call GPRJALRNonX7:$rs1)]>,
+                              PseudoInstExpansion<(JALR X1, GPR:$rs1, 0)>;
+}
 
 let isBarrier = 1, isReturn = 1, isTerminator = 1 in
 def PseudoRET : Pseudo<(outs), (ins), [(riscv_ret_glue)]>,
@@ -1502,10 +1524,16 @@ def PseudoTAIL : Pseudo<(outs), (ins call_symbol:$dst), [],
                         "tail", "$dst">,
                  Sched<[WriteIALU, WriteJalr, ReadJalr]>;
 
-let isCall = 1, isTerminator = 1, isReturn = 1, isBarrier = 1, Uses = [X2] in
+let isCall = 1, isTerminator = 1, isReturn = 1, isBarrier = 1, Uses = [X2] in {
+let Predicates = [NoStdExtZicfilp] in
 def PseudoTAILIndirect : Pseudo<(outs), (ins GPRTC:$rs1),
                                 [(riscv_tail GPRTC:$rs1)]>,
                          PseudoInstExpansion<(JALR X0, GPR:$rs1, 0)>;
+let Predicates = [HasStdExtZicfilp] in
+def PseudoTAILIndirectNonX7 : Pseudo<(outs), (ins GPRTCNonX7:$rs1),
+                                     [(riscv_tail GPRTCNonX7:$rs1)]>,
+                              PseudoInstExpansion<(JALR X0, GPR:$rs1, 0)>;
+}
 
 def : Pat<(riscv_tail (iPTR tglobaladdr:$dst)),
           (PseudoTAIL tglobaladdr:$dst)>;

llvm/lib/Target/RISCV/RISCVRegisterInfo.td

@@ -173,6 +173,8 @@ def GPRNoX0X2 : GPRRegisterClass<(sub GPR, X0, X2)>;
 // by tablegen.
 def GPRJALR : GPRRegisterClass<(sub GPR, (sequence "X%u", 0, 5))>;
 
+def GPRJALRNonX7 : GPRRegisterClass<(sub GPRJALR, X7)>;
+
 def GPRC : GPRRegisterClass<(add (sequence "X%u", 10, 15),
                                  (sequence "X%u", 8, 9))>;
 
@@ -183,6 +185,7 @@ def GPRC : GPRRegisterClass<(add (sequence "X%u", 10, 15),
 def GPRTC : GPRRegisterClass<(add (sequence "X%u", 6, 7),
                                   (sequence "X%u", 10, 17),
                                   (sequence "X%u", 28, 31))>;
+def GPRTCNonX7 : GPRRegisterClass<(sub GPRTC, X7)>;
 
 def SP : GPRRegisterClass<(add X2)>;
 

llvm/test/CodeGen/RISCV/zicfilp-indirect-branch.ll

@@ -0,0 +1,48 @@
+; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 3
+; RUN: llc -mtriple=riscv64 -stop-after=finalize-isel < %s | FileCheck %s
+; RUN: llc -mtriple=riscv64 -mattr=+experimental-zicfilp -stop-after=finalize-isel < %s | FileCheck -check-prefixes=ZICFILP %s
+
+@brind.arr = internal unnamed_addr constant [2 x ptr] [ptr blockaddress(@brind, %5), ptr blockaddress(@brind, %8)], align 8
+@x = dso_local global i32 0, align 4
+
+define void @brind(i32 noundef signext %0) {
+  ; CHECK-LABEL: name: brind
+  ; CHECK:   PseudoBRIND killed [[VAR:%.*]], 0
+  ; ZICFILP-LABEL: name: brind
+  ; ZICFILP:   PseudoBRINDNonX7 killed [[VAR:%.*]], 0
+  %2 = sext i32 %0 to i64
+  %3 = getelementptr inbounds [2 x ptr], ptr @brind.arr, i64 0, i64 %2
+  %4 = load ptr, ptr %3, align 8
+  indirectbr ptr %4, [label %5, label %8]
+
+5:                                                ; preds = %1
+  %6 = load i32, ptr @x, align 4
+  %7 = add nsw i32 %6, 2
+  store i32 %7, ptr @x, align 4
+  br label %8
+
+8:                                                ; preds = %5, %1
+  %9 = load i32, ptr @x, align 4
+  %10 = add nsw i32 %9, 1
+  store i32 %10, ptr @x, align 4
+  ret void
+}
+
+define i32 @indirect_call(ptr %0) {
+  ; CHECK-LABEL: name: indirect_call
+  ; CHECK: PseudoCALLIndirect
+  ; ZICFILP-LABEL: name: indirect_call
+  ; ZICFILP: PseudoCALLIndirectNonX7
+  call void %0()
+  ret i32 0
+}
+
+
+define void @indirect_tail(ptr %0) {
+  ; CHECK-LABEL: name: indirect_tail
+  ; CHECK: PseudoTAILIndirect
+  ; ZICFILP-LABEL: name: indirect_tail
+  ; ZICFILP: PseudoTAILIndirectNonX7
+  tail call void %0()
+  ret void
+}