[llvm] 4aa7fb7 - [AMDGPU] Revert scheduling to reduce spilling

[Stanislav Mekhanoshin via llvm-commits]

Author: Stanislav Mekhanoshin
Date: 2020-01-03T15:20:21-08:00
New Revision: 4aa7fb77527bee74e93e7cd8242f016c0f229236

URL: https://github.com/llvm/llvm-project/commit/4aa7fb77527bee74e93e7cd8242f016c0f229236
DIFF: https://github.com/llvm/llvm-project/commit/4aa7fb77527bee74e93e7cd8242f016c0f229236.diff

LOG: [AMDGPU] Revert scheduling to reduce spilling

We can revert region schedule if new schedule decreases occupancy.
However, if we already have only one wave we would accept any new
schedule even if it blows up register pressure. Such schedule may
result in quite heavy spilling which can be avoided if we reject
this new schedule.

Differential Revision: https://reviews.llvm.org/D72181

Added: 
    

Modified: 
    llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp

Removed: 
    


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diff  --git a/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp b/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp
index 973491a70d3c..e109eed5f607 100644
--- a/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp
+++ b/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp
@@ -16,6 +16,7 @@
 #include "SIInstrInfo.h"
 #include "SIMachineFunctionInfo.h"
 #include "SIRegisterInfo.h"
+#include "Utils/AMDGPUBaseInfo.h"
 #include "llvm/CodeGen/RegisterClassInfo.h"
 #include "llvm/Support/MathExtras.h"
 
@@ -389,8 +390,16 @@ void GCNScheduleDAGMILive::schedule() {
   }
 
   if (WavesAfter >= MinOccupancy) {
-    Pressure[RegionIdx] = PressureAfter;
-    return;
+    unsigned TotalVGPRs = AMDGPU::IsaInfo::getAddressableNumVGPRs(&ST);
+    unsigned TotalSGPRs = AMDGPU::IsaInfo::getAddressableNumSGPRs(&ST);
+    if (WavesAfter > MFI.getMinWavesPerEU() ||
+        PressureAfter.less(ST, PressureBefore) ||
+        (TotalVGPRs >= PressureAfter.getVGPRNum() &&
+         TotalSGPRs >= PressureAfter.getSGPRNum())) {
+      Pressure[RegionIdx] = PressureAfter;
+      return;
+    }
+    LLVM_DEBUG(dbgs() << "New pressure will result in more spilling.\n");
   }
 
   LLVM_DEBUG(dbgs() << "Attempting to revert scheduling.\n");