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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-risc-v

Author: Wang Pengcheng (wangpc-pp)

<details>
<summary>Changes</summary>

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.


---
Full diff: https://github.com/llvm/llvm-project/pull/68692.diff


3 Files Affected:

- (modified) llvm/lib/Target/RISCV/RISCVFeatures.td (+3) 
- (modified) llvm/lib/Target/RISCV/RISCVSubtarget.h (+4) 
- (modified) llvm/test/CodeGen/RISCV/macro-fusion-lui-addi.ll (+15) 


``````````diff
diff --git a/llvm/lib/Target/RISCV/RISCVFeatures.td b/llvm/lib/Target/RISCV/RISCVFeatures.td
index 3d3486b7fa89563..548579173f0ede4 100644
--- a/llvm/lib/Target/RISCV/RISCVFeatures.td
+++ b/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)"
diff --git a/llvm/lib/Target/RISCV/RISCVSubtarget.h b/llvm/lib/Target/RISCV/RISCVSubtarget.h
index 027d32d54160793..6b915e61c136086 100644
--- a/llvm/lib/Target/RISCV/RISCVSubtarget.h
+++ b/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);
   }
diff --git a/llvm/test/CodeGen/RISCV/macro-fusion-lui-addi.ll b/llvm/test/CodeGen/RISCV/macro-fusion-lui-addi.ll
index 7de0fd050d65867..18d1449d0e2e837 100644
--- a/llvm/test/CodeGen/RISCV/macro-fusion-lui-addi.ll
+++ b/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 at 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 at 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
 }

``````````

</details>


https://github.com/llvm/llvm-project/pull/68692