[RISCV] Make PostRAScheduler a target feature (#68692)

This is what AArch64 has done in https://reviews.llvm.org/D20762.

Tests are added in macro fusion tests, which uncover a bug that
DAG mutations don't take effect.

Author: wangpc-pp

llvm/lib/Target/RISCV/RISCVFeatures.td

@@ -902,6 +902,9 @@ def FeatureUnalignedVectorMem
                       "true", "Has reasonably performant unaligned vector "
                       "loads and stores">;
 
+def FeaturePostRAScheduler : SubtargetFeature<"use-postra-scheduler",
+    "UsePostRAScheduler", "true", "Schedule again after register allocation">;
+
 def TuneNoOptimizedZeroStrideLoad
    : SubtargetFeature<"no-optimized-zero-stride-load", "HasOptimizedZeroStrideLoad",
                       "false", "Hasn't optimized (perform fewer memory operations)"

llvm/lib/Target/RISCV/RISCVSubtarget.h

@@ -107,6 +107,10 @@ class RISCVSubtarget : public RISCVGenSubtargetInfo {
   }
   bool enableMachineScheduler() const override { return true; }
 
+  bool enablePostRAScheduler() const override {
+    return getSchedModel().PostRAScheduler || UsePostRAScheduler;
+  }
+
   Align getPrefFunctionAlignment() const {
     return Align(TuneInfo->PrefFunctionAlignment);
   }

llvm/test/CodeGen/RISCV/macro-fusion-lui-addi.ll

@@ -3,6 +3,8 @@
 ;RUN:   | FileCheck %s --check-prefix=NOFUSION
 ;RUN: llc < %s -mtriple=riscv64 -mattr=+f,+lui-addi-fusion -mcpu=sifive-u74 \
 ;RUN:   -target-abi=lp64f | FileCheck %s --check-prefix=FUSION
+;RUN: llc < %s -mtriple=riscv64 -mattr=+f,+lui-addi-fusion,+use-postra-scheduler -mcpu=sifive-u74 \
+;RUN:   -target-abi=lp64f | FileCheck %s --check-prefixes=FUSION-POSTRA
 
 @.str = private constant [4 x i8] c"%f\0A\00", align 1
 
@@ -20,6 +22,13 @@ define void @foo(i32 signext %0, i32 signext %1) {
 ; FUSION-NEXT:    lui a0, %hi(.L.str)
 ; FUSION-NEXT:    addi a0, a0, %lo(.L.str)
 ; FUSION-NEXT:    tail bar@plt
+;
+; FUSION-POSTRA-LABEL: foo:
+; FUSION-POSTRA:       # %bb.0:
+; FUSION-POSTRA-NEXT:    lui a0, %hi(.L.str)
+; FUSION-POSTRA-NEXT:    fcvt.s.w fa0, a1
+; FUSION-POSTRA-NEXT:    addi a0, a0, %lo(.L.str)
+; FUSION-POSTRA-NEXT:    tail bar@plt
   %3 = sitofp i32 %1 to float
   tail call void @bar(ptr @.str, float %3)
   ret void
@@ -40,5 +49,11 @@ define i32 @test_matint() {
 ; FUSION-NEXT:    lui a0, 1
 ; FUSION-NEXT:    addiw a0, a0, -2048
 ; FUSION-NEXT:    ret
+;
+; FUSION-POSTRA-LABEL: test_matint:
+; FUSION-POSTRA:       # %bb.0:
+; FUSION-POSTRA-NEXT:    lui a0, 1
+; FUSION-POSTRA-NEXT:    addiw a0, a0, -2048
+; FUSION-POSTRA-NEXT:    ret
   ret i32 2048
 }