[SOL] Fine tune memory operations threshold (#134)

Author: LucasSte

llvm/lib/Target/SBF/SBFISelLowering.cpp

@@ -170,15 +170,20 @@ SBFTargetLowering::SBFTargetLowering(const TargetMachine &TM,
     MaxStoresPerMemmove = MaxStoresPerMemmoveOptSize = 0;
     MaxLoadsPerMemcmp = 0;
   } else {
-    auto SelectionDAGInfo = STI.getSelectionDAGInfo();
-    // inline memcpy() for kernel to see explicit copy
-    unsigned CommonMaxStores =
-      SelectionDAGInfo->getCommonMaxStoresPerMemFunc();
-
-    MaxStoresPerMemset = MaxStoresPerMemsetOptSize = CommonMaxStores;
-    MaxStoresPerMemcpy = MaxStoresPerMemcpyOptSize = CommonMaxStores;
-    MaxStoresPerMemmove = MaxStoresPerMemmoveOptSize = CommonMaxStores;
-    MaxLoadsPerMemcmp = MaxLoadsPerMemcmpOptSize = CommonMaxStores;
+    // A syscall consumes at least 10 CUs, so we should only invoke it when
+    // the number of instructions is at least 10.
+
+    // Memset translates to stdw or stdxw, so the maximum should be 10.
+    MaxStoresPerMemset = MaxStoresPerMemsetOptSize = 10;
+    // Each store in memcpy follows a load, so the maximum is 5.
+    MaxStoresPerMemcpy = MaxStoresPerMemcpyOptSize = 5;
+    // Each store in memmove follows a load, so the maximum is 5.
+    MaxStoresPerMemmove = MaxStoresPerMemmoveOptSize = 5;
+    // Memcmp expands to three instructions for each load:
+    // 1. One load for each pointer being compared.
+    // 2. One jne for each load.
+    // The limit here should be three, since 3*3 = 9;
+    MaxLoadsPerMemcmp = MaxLoadsPerMemcmpOptSize = 3;
   }
 
   // CPU/Feature control

llvm/test/CodeGen/SBF/i128.ll

@@ -32,10 +32,9 @@ entry:
 }
 
 ; CHECK-LABEL: test
-; CHECK:       mov64 r7, r10
-; CHECK:       add64 r7, -32 
-; CHECK:       mov64 r1, r7
 ; CHECK:       stxw [r10 - 32], r{{[0-9]+}}
+; CHECK:       mov64 r1, r10
+; CHECK:       add64 r1, -32
 
 ; Function Attrs: argmemonly nounwind willreturn
 declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #1