[RISCV][RegAlloc] Add getCSRFirstUseCost for RISC-V

llvm/lib/CodeGen/RegAllocGreedy.cpp

@@ -2375,10 +2375,12 @@ void RAGreedy::aboutToRemoveInterval(const LiveInterval &LI) {
 }
 
 void RAGreedy::initializeCSRCost() {
-  // We use the larger one out of the command-line option and the value report
-  // by TRI.
+  // We use the command-line option if it is explicitly set, otherwise use the
+  // larger one out of the command-line option and the value reported by TRI.
   CSRCost = BlockFrequency(
-      std::max((unsigned)CSRFirstTimeCost, TRI->getCSRFirstUseCost()));
+      CSRFirstTimeCost.getNumOccurrences()
+          ? CSRFirstTimeCost
+          : std::max((unsigned)CSRFirstTimeCost, TRI->getCSRFirstUseCost()));
   if (!CSRCost.getFrequency())
     return;
 

llvm/lib/Target/RISCV/RISCVRegisterInfo.h

@@ -61,6 +61,13 @@ struct RISCVRegisterInfo : public RISCVGenRegisterInfo {
   const uint32_t *getCallPreservedMask(const MachineFunction &MF,
                                        CallingConv::ID) const override;
 
+  unsigned getCSRFirstUseCost() const override {
+    // The cost will be compared against BlockFrequency where entry has the
+    // value of 1 << 14. A value of 64 will choose to spill or split cold
+    // path instead of using a callee-saved register.
+    return 64;
+  }
+
   const MCPhysReg *getCalleeSavedRegs(const MachineFunction *MF) const override;
 
   const MCPhysReg *getIPRACSRegs(const MachineFunction *MF) const override;

llvm/test/CodeGen/RISCV/csr-first-use-cost.ll

@@ -0,0 +1,91 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc %s -mtriple=riscv64 -regalloc-csr-first-time-cost=0 | FileCheck %s -check-prefix=ZERO-COST
+; RUN: llc %s -mtriple=riscv64 -regalloc-csr-first-time-cost=64 | FileCheck %s -check-prefix=SOME-COST
+
+define fastcc void @Perl_sv_setnv(ptr %.str.54.3682) nounwind {
+; ZERO-COST-LABEL: Perl_sv_setnv:
+; ZERO-COST:       # %bb.0: # %entry
+; ZERO-COST-NEXT:    addi sp, sp, -32
+; ZERO-COST-NEXT:    sd ra, 24(sp) # 8-byte Folded Spill
+; ZERO-COST-NEXT:    sd s0, 16(sp) # 8-byte Folded Spill
+; ZERO-COST-NEXT:    sd s1, 8(sp) # 8-byte Folded Spill
+; ZERO-COST-NEXT:    bnez zero, .LBB0_5
+; ZERO-COST-NEXT:  # %bb.1: # %entry
+; ZERO-COST-NEXT:    li a1, 1
+; ZERO-COST-NEXT:    bnez a1, .LBB0_6
+; ZERO-COST-NEXT:  .LBB0_2: # %entry
+; ZERO-COST-NEXT:    mv s0, a0
+; ZERO-COST-NEXT:    beqz zero, .LBB0_4
+; ZERO-COST-NEXT:  # %bb.3: # %sw.bb34.i
+; ZERO-COST-NEXT:    li s0, 0
+; ZERO-COST-NEXT:  .LBB0_4: # %Perl_sv_reftype.exit
+; ZERO-COST-NEXT:    li s1, 0
+; ZERO-COST-NEXT:    li a0, 0
+; ZERO-COST-NEXT:    li a1, 0
+; ZERO-COST-NEXT:    jalr s1
+; ZERO-COST-NEXT:    li a0, 0
+; ZERO-COST-NEXT:    mv a1, s0
+; ZERO-COST-NEXT:    li a2, 0
+; ZERO-COST-NEXT:    jalr s1
+; ZERO-COST-NEXT:  .LBB0_5: # %entry
+; ZERO-COST-NEXT:    beqz zero, .LBB0_2
+; ZERO-COST-NEXT:  .LBB0_6: # %sw.bb3
+; ZERO-COST-NEXT:    ld ra, 24(sp) # 8-byte Folded Reload
+; ZERO-COST-NEXT:    ld s0, 16(sp) # 8-byte Folded Reload
+; ZERO-COST-NEXT:    ld s1, 8(sp) # 8-byte Folded Reload
+; ZERO-COST-NEXT:    addi sp, sp, 32
+; ZERO-COST-NEXT:    ret
+;
+; SOME-COST-LABEL: Perl_sv_setnv:
+; SOME-COST:       # %bb.0: # %entry
+; SOME-COST-NEXT:    addi sp, sp, -32
+; SOME-COST-NEXT:    sd ra, 24(sp) # 8-byte Folded Spill
+; SOME-COST-NEXT:    sd s0, 16(sp) # 8-byte Folded Spill
+; SOME-COST-NEXT:    bnez zero, .LBB0_5
+; SOME-COST-NEXT:  # %bb.1: # %entry
+; SOME-COST-NEXT:    li a1, 1
+; SOME-COST-NEXT:    bnez a1, .LBB0_6
+; SOME-COST-NEXT:  .LBB0_2: # %entry
+; SOME-COST-NEXT:    sd a0, 8(sp) # 8-byte Folded Spill
+; SOME-COST-NEXT:    beqz zero, .LBB0_4
+; SOME-COST-NEXT:  # %bb.3: # %sw.bb34.i
+; SOME-COST-NEXT:    sd zero, 8(sp) # 8-byte Folded Spill
+; SOME-COST-NEXT:  .LBB0_4: # %Perl_sv_reftype.exit
+; SOME-COST-NEXT:    li s0, 0
+; SOME-COST-NEXT:    li a0, 0
+; SOME-COST-NEXT:    li a1, 0
+; SOME-COST-NEXT:    jalr s0
+; SOME-COST-NEXT:    li a0, 0
+; SOME-COST-NEXT:    ld a1, 8(sp) # 8-byte Folded Reload
+; SOME-COST-NEXT:    li a2, 0
+; SOME-COST-NEXT:    jalr s0
+; SOME-COST-NEXT:  .LBB0_5: # %entry
+; SOME-COST-NEXT:    beqz zero, .LBB0_2
+; SOME-COST-NEXT:  .LBB0_6: # %sw.bb3
+; SOME-COST-NEXT:    ld ra, 24(sp) # 8-byte Folded Reload
+; SOME-COST-NEXT:    ld s0, 16(sp) # 8-byte Folded Reload
+; SOME-COST-NEXT:    addi sp, sp, 32
+; SOME-COST-NEXT:    ret
+entry:
+  switch i8 0, label %Perl_sv_reftype.exit [
+    i8 1, label %sw.bb4
+    i8 12, label %sw.bb34.i
+    i8 3, label %sw.bb3
+    i8 0, label %sw.bb3
+  ]
+
+sw.bb3:                                           ; preds = %entry, %entry
+  ret void
+
+sw.bb4:                                           ; preds = %entry
+  br label %Perl_sv_reftype.exit
+
+sw.bb34.i:                                        ; preds = %entry
+  br label %Perl_sv_reftype.exit
+
+Perl_sv_reftype.exit:                             ; preds = %sw.bb34.i, %sw.bb4, %entry
+  %retval.0.i = phi ptr [ null, %sw.bb34.i ], [ null, %sw.bb4 ], [ %.str.54.3682, %entry ]
+  %call17 = tail call fastcc i64 null(ptr null, i32 0)
+  tail call void (ptr, ...) null(ptr null, ptr %retval.0.i, ptr null)
+  unreachable
+}