[PATCH] D63741: [TableGen] Add "InitValue": Handle operands with set bit values in decoder methods

[Nicolas Guillemot via Phabricator via llvm-commits]

nlguillemot created this revision.
nlguillemot added reviewers: craig.topper, dsanders.

The problem:

  When an operand had bits explicitly set to "1" (as in the InitValue.td test case attached), the decoder was ignoring those bits, and the DecoderMethod was receiving an input where the bits were still zero.

The solution:

  We added an "InitValue" variable that stores the initial value of the operand based on what bits were explicitly initialized to 1 in TableGen code. The generated decoder code then uses that initial value to initialize the "tmp" variable, then calls fieldFromInstruction to read the values for the remaining bits that were left unknown in TableGen.

This is mainly useful when there are variations of an instruction that differ based on what bits are set in the operands, since this change makes it possible to access those bits in a DecoderMethod. The DecoderMethod can use those bits to know how to handle the input.


https://reviews.llvm.org/D63741

Files:
  test/TableGen/FixedLenDecoderEmitter/InitValue.td
  utils/TableGen/FixedLenDecoderEmitter.cpp


Index: utils/TableGen/FixedLenDecoderEmitter.cpp
===================================================================
--- utils/TableGen/FixedLenDecoderEmitter.cpp
+++ utils/TableGen/FixedLenDecoderEmitter.cpp
@@ -64,9 +64,10 @@
   std::vector<EncodingField> Fields;
   std::string Decoder;
   bool HasCompleteDecoder;
+  uint64_t InitValue;
 
   OperandInfo(std::string D, bool HCD)
-      : Decoder(std::move(D)), HasCompleteDecoder(HCD) {}
+      : Decoder(std::move(D)), HasCompleteDecoder(HCD), InitValue(0) {}
 
   void addField(unsigned Base, unsigned Width, unsigned Offset) {
     Fields.push_back(EncodingField(Base, Width, Offset));
@@ -1103,12 +1104,15 @@
                                      bool &OpHasCompleteDecoder) const {
   const std::string &Decoder = OpInfo.Decoder;
 
-  if (OpInfo.numFields() != 1)
-    o.indent(Indentation) << "tmp = 0;\n";
+  if (OpInfo.numFields() != 1 || OpInfo.InitValue != 0) {
+    o.indent(Indentation) << "tmp = 0x";
+    o.write_hex(OpInfo.InitValue);
+    o << ";\n";
+  }
 
   for (const EncodingField &EF : OpInfo) {
     o.indent(Indentation) << "tmp ";
-    if (OpInfo.numFields() != 1) o << '|';
+    if (OpInfo.numFields() != 1 || OpInfo.InitValue != 0) o << '|';
     o << "= fieldFromInstruction"
       << "(insn, " << EF.Base << ", " << EF.Width << ')';
     if (OpInfo.numFields() != 1 || EF.Offset != 0)
@@ -2026,6 +2030,16 @@
       HasCompleteDecoderBit->getValue() : true;
 
     OperandInfo OpInfo(Decoder, HasCompleteDecoder);
+
+    // Some bits of the operand may be required to be 1 depending on the
+    // instruction's encoding. Collect those bits.
+    if (const RecordVal *EncodedValue = EncodingDef.getValue(Op.second))
+      if (const BitsInit *OpBits = dyn_cast<BitsInit>(EncodedValue->getValue()))
+        for (unsigned I = 0; I < OpBits->getNumBits(); ++I)
+          if (const BitInit *OpBit = dyn_cast<BitInit>(OpBits->getBit(I)))
+            if (OpBit->getValue())
+              OpInfo.InitValue |= 1 << I;
+
     unsigned Base = ~0U;
     unsigned Width = 0;
     unsigned Offset = 0;
Index: test/TableGen/FixedLenDecoderEmitter/InitValue.td
===================================================================
--- test/TableGen/FixedLenDecoderEmitter/InitValue.td
+++ test/TableGen/FixedLenDecoderEmitter/InitValue.td
@@ -0,0 +1,35 @@
+// RUN: llvm-tblgen -gen-disassembler -I %p/../../../include %s | FileCheck %s
+
+include "llvm/Target/Target.td"
+
+def archInstrInfo : InstrInfo { }
+
+def arch : Target {
+    let InstructionSet = archInstrInfo;
+}
+
+let OutOperandList = (outs), Size = 2 in {
+
+def foo : Instruction {
+    let InOperandList = (ins i32imm:$factor);
+    field bits<16> Inst;
+    field bits<16> SoftFail = 0;
+    bits<8> factor;
+    let factor{0} = 0; // zero initial value
+    let Inst{15-8} = factor{7-0};
+    }
+
+def bar : Instruction {
+    let InOperandList = (ins i32imm:$factor);
+    field bits<16> Inst;
+    field bits<16> SoftFail = 0;
+    bits<8> factor;
+    let factor{0} = 1; // non-zero initial value
+    let Inst{15-8} = factor{7-0};
+    }
+
+}
+
+// CHECK: tmp = fieldFromInstruction(insn, 9, 7) << 1;
+// CHECK: tmp = 0x1;
+// CHECK: tmp |= fieldFromInstruction(insn, 9, 7) << 1;


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D63741.206305.patch
Type: text/x-patch
Size: 3223 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20190624/87602c20/attachment.bin>