[PATCH] D96317: [TableGen][SelectionDAG] Improve efficiency of encoding negative immediates for isel's CheckInteger opcode.

[Craig Topper via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG61d4d9a5d335: [TableGen][SelectionDAG] Improve efficiency of encoding negative immediates for… (authored by craig.topper).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D96317/new/

https://reviews.llvm.org/D96317

Files:
  llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
  llvm/test/TableGen/dag-isel-regclass-emit-enum.td
  llvm/test/TableGen/dag-isel-subregs.td
  llvm/utils/TableGen/DAGISelMatcherEmitter.cpp


Index: llvm/utils/TableGen/DAGISelMatcherEmitter.cpp
===================================================================
--- llvm/utils/TableGen/DAGISelMatcherEmitter.cpp
+++ llvm/utils/TableGen/DAGISelMatcherEmitter.cpp
@@ -206,6 +206,18 @@
   return NumBytes+1;
 }
 
+/// Emit the specified signed value as a VBR. To improve compression we encode
+/// positive numbers shifted left by 1 and negative numbers negated and shifted
+/// left by 1 with bit 0 set.
+static unsigned EmitSignedVBRValue(uint64_t Val, raw_ostream &OS) {
+  if ((int64_t)Val >= 0)
+    Val = Val << 1;
+  else
+    Val = (-Val << 1) | 1;
+
+  return EmitVBRValue(Val, OS);
+}
+
 // This is expensive and slow.
 static std::string getIncludePath(const Record *R) {
   std::string str;
@@ -579,15 +591,16 @@
 
   case Matcher::CheckInteger: {
     OS << "OPC_CheckInteger, ";
-    unsigned Bytes=1+EmitVBRValue(cast<CheckIntegerMatcher>(N)->getValue(), OS);
+    unsigned Bytes =
+        1 + EmitSignedVBRValue(cast<CheckIntegerMatcher>(N)->getValue(), OS);
     OS << '\n';
     return Bytes;
   }
   case Matcher::CheckChildInteger: {
     OS << "OPC_CheckChild" << cast<CheckChildIntegerMatcher>(N)->getChildNo()
        << "Integer, ";
-    unsigned Bytes=1+EmitVBRValue(cast<CheckChildIntegerMatcher>(N)->getValue(),
-                                  OS);
+    unsigned Bytes = 1 + EmitSignedVBRValue(
+                             cast<CheckChildIntegerMatcher>(N)->getValue(), OS);
     OS << '\n';
     return Bytes;
   }
Index: llvm/test/TableGen/dag-isel-subregs.td
===================================================================
--- llvm/test/TableGen/dag-isel-subregs.td
+++ llvm/test/TableGen/dag-isel-subregs.td
@@ -8,7 +8,7 @@
 def : Pat<(v2i32 (extract_subvector v32i32:$src, (i32 0))),
           (EXTRACT_SUBREG GPR_1024:$src, sub0_sub1)>;
 
-// CHECK: OPC_CheckChild1Integer, 15,
+// CHECK: OPC_CheckChild1Integer, 30,
 // CHECK: OPC_EmitInteger, MVT::i32, 5|128,1/*133*/,
 def : Pat<(v2i32 (extract_subvector v32i32:$src, (i32 15))),
           (EXTRACT_SUBREG GPR_1024:$src, sub30_sub31)>;
Index: llvm/test/TableGen/dag-isel-regclass-emit-enum.td
===================================================================
--- llvm/test/TableGen/dag-isel-regclass-emit-enum.td
+++ llvm/test/TableGen/dag-isel-regclass-emit-enum.td
@@ -31,7 +31,7 @@
 def : Pat<(i32 (add i32:$src, (i32 0))),
           (COPY_TO_REGCLASS GPRAbove127, GPR0:$src)>;
 
-// CHECK:      OPC_CheckChild1Integer, 1,
+// CHECK:      OPC_CheckChild1Integer, 2,
 // CHECK-NEXT: OPC_EmitInteger, MVT::i32, TestNamespace::GPR127RegClassID,
 // CHECK-NEXT: OPC_MorphNodeTo1, TARGET_VAL(TargetOpcode::COPY_TO_REGCLASS), 0,
 // CHECK-NEXT:     MVT::i32, 2/*#Ops*/, 1, 0,
Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -2578,6 +2578,17 @@
   return VT == MVT::iPTR && cast<VTSDNode>(N)->getVT() == TLI->getPointerTy(DL);
 }
 
+// Bit 0 stores the sign of the immediate. The upper bits contain the magnitude
+// shifted left by 1.
+static uint64_t decodeSignRotatedValue(uint64_t V) {
+  if ((V & 1) == 0)
+    return V >> 1;
+  if (V != 1)
+    return -(V >> 1);
+  // There is no such thing as -0 with integers.  "-0" really means MININT.
+  return 1ULL << 63;
+}
+
 LLVM_ATTRIBUTE_ALWAYS_INLINE static bool
 CheckInteger(const unsigned char *MatcherTable, unsigned &MatcherIndex,
              SDValue N) {
@@ -2585,6 +2596,8 @@
   if (Val & 128)
     Val = GetVBR(Val, MatcherTable, MatcherIndex);
 
+  Val = decodeSignRotatedValue(Val);
+
   ConstantSDNode *C = dyn_cast<ConstantSDNode>(N);
   return C && C->getSExtValue() == Val;
 }


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