[RISCV] Update the latencies of MUL and CPOP in SiFive P400 scheduling model (llvm#122007)

According to llvm-exegesis, they should have around 2 cycles of latency
on P400 cores.

Author: mshockwave

llvm/lib/Target/RISCV/RISCVSchedSiFiveP400.td

@@ -182,7 +182,7 @@ def P400WriteCMOV : SchedWriteRes<[SiFiveP400Branch, SiFiveP400IEXQ1]> {
 }
 def : InstRW<[P400WriteCMOV], (instrs PseudoCCMOVGPRNoX0)>;
 
-let Latency = 3 in {
+let Latency = 2 in {
 // Integer multiplication
 def : WriteRes<WriteIMul, [SiFiveP400MulDiv]>;
 def : WriteRes<WriteIMul32, [SiFiveP400MulDiv]>;

llvm/test/tools/llvm-mca/RISCV/SiFiveP400/mul-cpop.s

@@ -0,0 +1,60 @@
+# NOTE: Assertions have been autogenerated by utils/update_mca_test_checks.py
+# RUN: llvm-mca -mtriple=riscv64 -mcpu=sifive-p470 -iterations=1 < %s | FileCheck %s
+
+mul s6, s6, s7
+
+mulw s4, s4, a2
+
+cpop t1, t1
+
+cpopw t2, t2
+
+# CHECK:      Iterations:        1
+# CHECK-NEXT: Instructions:      4
+# CHECK-NEXT: Total Cycles:      8
+# CHECK-NEXT: Total uOps:        4
+
+# CHECK:      Dispatch Width:    3
+# CHECK-NEXT: uOps Per Cycle:    0.50
+# CHECK-NEXT: IPC:               0.50
+# CHECK-NEXT: Block RThroughput: 4.0
+
+# CHECK:      Instruction Info:
+# CHECK-NEXT: [1]: #uOps
+# CHECK-NEXT: [2]: Latency
+# CHECK-NEXT: [3]: RThroughput
+# CHECK-NEXT: [4]: MayLoad
+# CHECK-NEXT: [5]: MayStore
+# CHECK-NEXT: [6]: HasSideEffects (U)
+
+# CHECK:      [1]    [2]    [3]    [4]    [5]    [6]    Instructions:
+# CHECK-NEXT:  1      2     1.00                        mul	s6, s6, s7
+# CHECK-NEXT:  1      2     1.00                        mulw	s4, s4, a2
+# CHECK-NEXT:  1      2     1.00                        cpop	t1, t1
+# CHECK-NEXT:  1      2     1.00                        cpopw	t2, t2
+
+# CHECK:      Resources:
+# CHECK-NEXT: [0]   - SiFiveP400Div
+# CHECK-NEXT: [1]   - SiFiveP400FEXQ0
+# CHECK-NEXT: [2]   - SiFiveP400FloatDiv
+# CHECK-NEXT: [3]   - SiFiveP400IEXQ0
+# CHECK-NEXT: [4]   - SiFiveP400IEXQ1
+# CHECK-NEXT: [5]   - SiFiveP400IEXQ2
+# CHECK-NEXT: [6]   - SiFiveP400Load
+# CHECK-NEXT: [7]   - SiFiveP400Store
+# CHECK-NEXT: [8]   - SiFiveP400VDiv
+# CHECK-NEXT: [9]   - SiFiveP400VEXQ0
+# CHECK-NEXT: [10]  - SiFiveP400VFloatDiv
+# CHECK-NEXT: [11]  - SiFiveP400VLD
+# CHECK-NEXT: [12]  - SiFiveP400VST
+
+# CHECK:      Resource pressure per iteration:
+# CHECK-NEXT: [0]    [1]    [2]    [3]    [4]    [5]    [6]    [7]    [8]    [9]    [10]   [11]   [12]
+# CHECK-NEXT:  -      -      -      -      -     4.00    -      -      -      -      -      -      -
+
+# CHECK:      Resource pressure by instruction:
+# CHECK-NEXT: [0]    [1]    [2]    [3]    [4]    [5]    [6]    [7]    [8]    [9]    [10]   [11]   [12]   Instructions:
+# CHECK-NEXT:  -      -      -      -      -     1.00    -      -      -      -      -      -      -     mul	s6, s6, s7
+# CHECK-NEXT:  -      -      -      -      -     1.00    -      -      -      -      -      -      -     mulw	s4, s4, a2
+# CHECK-NEXT:  -      -      -      -      -     1.00    -      -      -      -      -      -      -     cpop	t1, t1
+# CHECK-NEXT:  -      -      -      -      -     1.00    -      -      -      -      -      -      -     cpopw	t2, t2