AMDGPU/SI: Use a better method for determining the largest pressure sets

Summary:
There are a few different sgpr pressure sets, but we only care about
the one which covers all of the sgprs.  We were using hard-coded
register pressure set names to determine the reg set id for the
biggest sgpr set.  However, we were using the wrong name, and this
method is pretty fragile, since the reg pressure set names may
change.

The new method just looks for the pressure set that contains the most
reg units and sets that set as our SGPR pressure set.  We've also
adopted the same technique for determining our VGPR pressure set.

Reviewers: arsenm

Subscribers: MatzeB, arsenm, llvm-commits, kzhuravl

Differential Revision: https://reviews.llvm.org/D23687

llvm-svn: 279867

3 files changed, 41 insertions, 15 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIMachineScheduler.cpp b/llvm/lib/Target/AMDGPU/SIMachineScheduler.cpp
index 3b1a9d54f44..0adf1c4ce1f 100644
--- a/llvm/lib/Target/AMDGPU/SIMachineScheduler.cpp
+++ b/llvm/lib/Target/AMDGPU/SIMachineScheduler.cpp
@@ -1657,8 +1657,8 @@ SIScheduleDAGMI::SIScheduleDAGMI(MachineSchedContext *C) :
   SITII = static_cast<const SIInstrInfo*>(TII);
   SITRI = static_cast<const SIRegisterInfo*>(TRI);
 
-  VGPRSetID = SITRI->getVGPR32PressureSet();
-  SGPRSetID = SITRI->getSGPR32PressureSet();
+  VGPRSetID = SITRI->getVGPRPressureSet();
+  SGPRSetID = SITRI->getSGPRPressureSet();
 }
 
 SIScheduleDAGMI::~SIScheduleDAGMI() {
diff --git a/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp b/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
index a1c83f5d736..90eda52a8c1 100644
--- a/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
@@ -95,19 +95,38 @@ SIRegisterInfo::SIRegisterInfo() : AMDGPURegisterInfo(),
                                    VGPRPressureSets(getNumRegPressureSets()) {
   unsigned NumRegPressureSets = getNumRegPressureSets();
 
-  SGPR32SetID = NumRegPressureSets;
-  VGPR32SetID = NumRegPressureSets;
-  for (unsigned i = 0; i < NumRegPressureSets; ++i) {
-    if (strncmp("SGPR_32", getRegPressureSetName(i), 7) == 0)
-      SGPR32SetID = i;
-    else if (strncmp("VGPR_32", getRegPressureSetName(i), 7) == 0)
-      VGPR32SetID = i;
+  SGPRSetID = NumRegPressureSets;
+  VGPRSetID = NumRegPressureSets;
 
+  for (unsigned i = 0; i < NumRegPressureSets; ++i) {
     classifyPressureSet(i, AMDGPU::SGPR0, SGPRPressureSets);
     classifyPressureSet(i, AMDGPU::VGPR0, VGPRPressureSets);
   }
-  assert(SGPR32SetID < NumRegPressureSets &&
-         VGPR32SetID < NumRegPressureSets);
+
+  // Determine the number of reg units for each pressure set.
+  std::vector<unsigned> PressureSetRegUnits(NumRegPressureSets, 0);
+  for (unsigned i = 0, e = getNumRegUnits(); i != e; ++i) {
+    const int *PSets = getRegUnitPressureSets(i);
+    for (unsigned j = 0; PSets[j] != -1; ++j) {
+      PressureSetRegUnits[PSets[j]]++;
+    }
+  }
+
+  unsigned VGPRMax = 0, SGPRMax = 0;
+  for (unsigned i = 0; i < NumRegPressureSets; ++i) {
+    if (isVGPRPressureSet(i) && PressureSetRegUnits[i] > VGPRMax) {
+      VGPRSetID = i;
+      VGPRMax = PressureSetRegUnits[i];
+      continue;
+    }
+    if (isSGPRPressureSet(i) && PressureSetRegUnits[i] > SGPRMax) {
+      SGPRSetID = i;
+      SGPRMax = PressureSetRegUnits[i];
+    }
+  }
+
+  assert(SGPRSetID < NumRegPressureSets &&
+         VGPRSetID < NumRegPressureSets);
 }
 
 void SIRegisterInfo::reserveRegisterTuples(BitVector &Reserved, unsigned Reg) const {
diff --git a/llvm/lib/Target/AMDGPU/SIRegisterInfo.h b/llvm/lib/Target/AMDGPU/SIRegisterInfo.h
index 087631db684..b0e852e6127 100644
--- a/llvm/lib/Target/AMDGPU/SIRegisterInfo.h
+++ b/llvm/lib/Target/AMDGPU/SIRegisterInfo.h
@@ -25,8 +25,8 @@ class MachineRegisterInfo;
 
 struct SIRegisterInfo final : public AMDGPURegisterInfo {
 private:
-  unsigned SGPR32SetID;
-  unsigned VGPR32SetID;
+  unsigned SGPRSetID;
+  unsigned VGPRSetID;
   BitVector SGPRPressureSets;
   BitVector VGPRPressureSets;
 
@@ -182,11 +182,18 @@ public:
                               const TargetRegisterClass *RC,
                               const MachineFunction &MF) const;
 
-  unsigned getSGPR32PressureSet() const { return SGPR32SetID; };
-  unsigned getVGPR32PressureSet() const { return VGPR32SetID; };
+  unsigned getSGPRPressureSet() const { return SGPRSetID; };
+  unsigned getVGPRPressureSet() const { return VGPRSetID; };
 
   bool isVGPR(const MachineRegisterInfo &MRI, unsigned Reg) const;
 
+  bool isSGPRPressureSet(unsigned SetID) const {
+    return SGPRPressureSets.test(SetID) && !VGPRPressureSets.test(SetID);
+  }
+  bool isVGPRPressureSet(unsigned SetID) const {
+    return VGPRPressureSets.test(SetID) && !SGPRPressureSets.test(SetID);
+  }
+
 private:
   void buildScratchLoadStore(MachineBasicBlock::iterator MI,
                              unsigned LoadStoreOp, const MachineOperand *SrcDst,