[AMDGPU] Make the iterative schedulers selectable via amdgpu-sched-strategy (#135042)

Currently, the only way for users to try these schedulers is via
`-misched=` . However, this overrides the default scheduler for all
targets. This causes problems for various toolchains / drivers which
spawn jobs for both x86 and AMDGPU -- e.g. hipcc. On the other hand,
`amdgpu-sched-strategy` only changes the scheduler for AMDGPU target.

Author: jrbyrnes

llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp

@@ -1088,6 +1088,15 @@ GCNTargetMachine::createMachineScheduler(MachineSchedContext *C) const {
   if (SchedStrategy == "max-memory-clause")
     return createGCNMaxMemoryClauseMachineScheduler(C);
 
+  if (SchedStrategy == "iterative-ilp")
+    return createIterativeILPMachineScheduler(C);
+
+  if (SchedStrategy == "iterative-minreg")
+    return createMinRegScheduler(C);
+
+  if (SchedStrategy == "iterative-maxocc")
+    return createIterativeGCNMaxOccupancyMachineScheduler(C);
+
   return createGCNMaxOccupancyMachineScheduler(C);
 }
 

llvm/test/CodeGen/AMDGPU/schedule-regpressure-limit2.ll

@@ -1,7 +1,11 @@
 ; RUN: llc -mtriple=amdgcn -mcpu=tahiti -enable-amdgpu-aa=0 -misched=gcn-iterative-minreg -verify-machineinstrs < %s | FileCheck --check-prefix=SI-MINREG %s
 ; RUN: llc -mtriple=amdgcn -mcpu=tahiti -enable-amdgpu-aa=0 -misched=gcn-iterative-max-occupancy-experimental -verify-machineinstrs < %s | FileCheck --check-prefix=SI-MAXOCC %s
+; RUN: llc -mtriple=amdgcn -mcpu=tahiti -enable-amdgpu-aa=0 -amdgpu-sched-strategy=iterative-minreg -verify-machineinstrs < %s | FileCheck --check-prefix=SI-MINREG %s
+; RUN: llc -mtriple=amdgcn -mcpu=tahiti -enable-amdgpu-aa=0 -amdgpu-sched-strategy=iterative-maxocc -verify-machineinstrs < %s | FileCheck --check-prefix=SI-MAXOCC %s
 ; RUN: llc -mtriple=amdgcn -mcpu=fiji -enable-amdgpu-aa=0 -misched=gcn-iterative-minreg -verify-machineinstrs < %s | FileCheck --check-prefix=VI %s
 ; RUN: llc -mtriple=amdgcn -mcpu=fiji -enable-amdgpu-aa=0 -misched=gcn-iterative-max-occupancy-experimental -verify-machineinstrs < %s | FileCheck --check-prefix=VI %s
+; RUN: llc -mtriple=amdgcn -mcpu=fiji -enable-amdgpu-aa=0 -amdgpu-sched-strategy=iterative-minreg -verify-machineinstrs < %s | FileCheck --check-prefix=VI %s
+; RUN: llc -mtriple=amdgcn -mcpu=fiji -enable-amdgpu-aa=0 -amdgpu-sched-strategy=iterative-maxocc -verify-machineinstrs < %s | FileCheck --check-prefix=VI %s
 
 ; SI-MINREG: NumSgprs: {{[1-9]$}}
 ; SI-MINREG: NumVgprs: {{[1-9]$}}

llvm/test/CodeGen/AMDGPU/schedule-regpressure-limit3.ll

@@ -1,5 +1,6 @@
 ; RUN: llc -mtriple=amdgcn -mcpu=tonga -verify-machineinstrs < %s | FileCheck --check-prefix=MISCHED %s
 ; RUN: llc -mtriple=amdgcn -mcpu=tonga -misched=gcn-iterative-ilp -verify-machineinstrs < %s | FileCheck --check-prefix=GCN-ILP %s
+; RUN: llc -mtriple=amdgcn -mcpu=tonga -amdgpu-sched-strategy=iterative-ilp -verify-machineinstrs < %s | FileCheck --check-prefix=GCN-ILP %s
 
 ; Test the scheduler when only one wave is requested. The result should be high register usage and max ILP.