[llvm] [TableGen] Use bitwise operations to access HwMode ID. (PR #88377)

[Jason Eckhardt via llvm-commits]

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@@ -290,11 +290,55 @@ CodeEmitterGen::getInstructionCases(Record *R, CodeGenTarget &Target) {
     if (auto *DI = dyn_cast_or_null<DefInit>(RV->getValue())) {
       const CodeGenHwModes &HWM = Target.getHwModes();
       EncodingInfoByHwMode EBM(DI->getDef(), HWM);
+      unsigned EncodingHwModesInBits = DefaultMode;
+      for (auto &[ModeId, Encoding] : EBM) {
+        // DefaultMode is 0, skip it.
+        if (ModeId != DefaultMode)
+          EncodingHwModesInBits |= (1 << (ModeId - 1));
+      }
+
+      // Get HwModes for this Instr by bitwise AND operations,
+      // and find the table to which this instr and hwmode belong.
+      append("      unsigned HwMode = "
+             "STI.getHwMode(MCSubtargetInfo::HwMode_EncodingInfo);\n");
+      append("      HwMode &= " + itostr(EncodingHwModesInBits) + ";\n");
+      append("      switch (HwMode) {\n");
+      append("      default: llvm_unreachable(\"Unknown hardware mode!\"); "
+             "break;\n");
+      for (auto &[ModeId, Encoding] : EBM) {
+        if (ModeId == DefaultMode) {
+          append("      case " + itostr(DefaultMode) +
+                 ": InstBitsByHw = InstBits");
+        } else {
+          append("      case " + itostr(1 << (ModeId - 1)) +
+                 ": InstBitsByHw = InstBits_" +
+                 std::string(HWM.getMode(ModeId).Name));
+        }
+        append("; break;\n");
+      }
+      append("      };\n");
+
+      // We need to remodify the 'Inst' value from the table we found above.
+      if (UseAPInt) {
+        int NumWords = APInt::getNumWords(BitWidth);
+        append("      Inst = APInt(" + itostr(BitWidth));
+        append(", ArrayRef(InstBitsByHw + opcode * " + itostr(NumWords) + ", " +
+               itostr(NumWords));
+        append("));\n");
+        append("      Value = Inst;\n");
+      } else {
+        append("      Value = InstBitsByHw[opcode];\n");
+      }
+
       append("      switch (HwMode) {\n");
       append("      default: llvm_unreachable(\"Unhandled HwMode\");\n");
-      for (auto &KV : EBM) {
-        append(("      case " + itostr(KV.first) + ": {\n").c_str());
-        addInstructionCasesForEncoding(R, KV.second, Target, Case,
+      for (auto &[ModeId, Encoding] : EBM) {
+        if (ModeId == DefaultMode) {
+          append("      case " + itostr(DefaultMode) + ": {\n");
+        } else {
+          append("      case " + itostr(1 << (ModeId - 1)) + ": {\n");
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nvjle wrote:

Same issue here.

https://github.com/llvm/llvm-project/pull/88377