[llvm] [AMDGPU][Scheduler] Refactor ArchVGPR rematerialization during scheduling (PR #125885)

[Jeffrey Byrnes via llvm-commits]

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@@ -1673,174 +1682,333 @@ bool PreRARematStage::allUsesAvailableAt(const MachineInstr *InstToRemat,
   return true;
 }
 
-void PreRARematStage::collectRematerializableInstructions() {
-  const SIRegisterInfo *SRI = static_cast<const SIRegisterInfo *>(DAG.TRI);
-  for (unsigned I = 0, E = DAG.MRI.getNumVirtRegs(); I != E; ++I) {
-    Register Reg = Register::index2VirtReg(I);
-    if (!DAG.LIS->hasInterval(Reg))
-      continue;
-
-    // TODO: Handle AGPR and SGPR rematerialization
-    if (!SRI->isVGPRClass(DAG.MRI.getRegClass(Reg)) ||
-        !DAG.MRI.hasOneDef(Reg) || !DAG.MRI.hasOneNonDBGUse(Reg))
-      continue;
+bool PreRARematStage::hasExcessVGPRs(const GCNRegPressure &RP,
+                                     unsigned MaxVGPRs,
+                                     unsigned &ExcessArchVGPRs,
+                                     bool &AGPRLimited) {
+  unsigned NumAGPRs = RP.getAGPRNum();
+  if (!ST.hasGFX90AInsts() || !NumAGPRs) {
+    // Non-unified RF. We can only reduce ArchVGPR excess pressure at this
+    // point, but still want to identify when there is AGPR excess pressure.
+    bool HasSpill = false;
+    unsigned NumArchVGPRs = RP.getArchVGPRNum();
+    if (NumArchVGPRs > MaxVGPRs) {
+      ExcessArchVGPRs = NumArchVGPRs - MaxVGPRs;
+      HasSpill = true;
+    }
+    if (NumAGPRs > MaxVGPRs) {
+      ExcessArchVGPRs = NumArchVGPRs;
+      AGPRLimited = true;
+      HasSpill = true;
+    }
+    return HasSpill;
+  }
+  if (RP.getVGPRNum(true) > MaxVGPRs) {
----------------
jrbyrnes wrote:

We should also take into account the limits of each of accvgpr and archvgpr.

For example, if we have 262 archgpr and 252 accvgpr, we have 514 vgpr (>= MaxVGPRs of 512 assuming occ lowerbound of 1, gfx942). 

This calculatuion determines ExcessArchVGPR = 262 - alignDown(512-252,4) = 2, but we really have ExcessArchVGPR of 6 due to archvgpr limit.

Something like this:

ExceedRF, ExceedArch, ExceedAcc -> ExcessArchVGPRs

{1,1,0} -> arch excess
{1,0,1} -> min (acc excess, arch usage)
{1,1,1} -> max (min (total excess, arch usage), min (acc excess, arch usage), arch excess)



https://github.com/llvm/llvm-project/pull/125885