[llvm] r328136 - [X86] Rewrite getOperandBias in X86BaseInfo.h to be a little more structured and update comments to be more clear about what it does. NFC

[Craig Topper via llvm-commits]

Author: ctopper
Date: Wed Mar 21 12:30:28 2018
New Revision: 328136

URL: http://llvm.org/viewvc/llvm-project?rev=328136&view=rev
Log:
[X86] Rewrite getOperandBias in X86BaseInfo.h to be a little more structured and update comments to be more clear about what it does. NFC

Modified:
    llvm/trunk/lib/Target/X86/MCTargetDesc/X86BaseInfo.h

Modified: llvm/trunk/lib/Target/X86/MCTargetDesc/X86BaseInfo.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/MCTargetDesc/X86BaseInfo.h?rev=328136&r1=328135&r2=328136&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/MCTargetDesc/X86BaseInfo.h (original)
+++ llvm/trunk/lib/Target/X86/MCTargetDesc/X86BaseInfo.h Wed Mar 21 12:30:28 2018
@@ -646,30 +646,40 @@ namespace X86II {
     }
   }
 
-  /// getOperandBias - compute any additional adjustment needed to
-  ///                  the offset to the start of the memory operand
-  ///                  in this instruction.
-  /// If this is a two-address instruction,skip one of the register operands.
-  /// FIXME: This should be handled during MCInst lowering.
-  inline unsigned getOperandBias(const MCInstrDesc& Desc)
-  {
+  /// getOperandBias - compute whether all of the def operands are repeated
+  ///                  in the uses and therefore should be skipped.
+  /// This determines the start of the unique operand list. We need to determine
+  /// if all of the defs have a corresponding tied operand in the uses.
+  /// Unfortunately, the tied operand information is encoded in the uses not
+  /// the defs so we have to use some heuristics to find which operands to
+  /// query.
+  inline unsigned getOperandBias(const MCInstrDesc& Desc) {
+    unsigned NumDefs = Desc.getNumDefs();
     unsigned NumOps = Desc.getNumOperands();
-    if (NumOps > 1 && Desc.getOperandConstraint(1, MCOI::TIED_TO) == 0)
-      return 1;
-    if (NumOps > 3 && Desc.getOperandConstraint(2, MCOI::TIED_TO) == 0 &&
-        Desc.getOperandConstraint(3, MCOI::TIED_TO) == 1)
-      // Special case for AVX-512 GATHER with 2 TIED_TO operands
-      // Skip the first 2 operands: dst, mask_wb
-      return 2;
-    if (NumOps > 3 && Desc.getOperandConstraint(2, MCOI::TIED_TO) == 0 &&
-        Desc.getOperandConstraint(NumOps - 1, MCOI::TIED_TO) == 1)
-      // Special case for GATHER with 2 TIED_TO operands
-      // Skip the first 2 operands: dst, mask_wb
-      return 2;
-    if (NumOps > 2 && Desc.getOperandConstraint(NumOps - 2, MCOI::TIED_TO) == 0)
-      // SCATTER
-      return 1;
-    return 0;
+    switch (NumDefs) {
+    default: llvm_unreachable("Unexpected number of defs");
+    case 0:
+      return 0;
+    case 1:
+      // Common two addr case.
+      if (NumOps > 1 && Desc.getOperandConstraint(1, MCOI::TIED_TO) == 0)
+        return 1;
+      // Check for AVX-512 scatter which has a TIED_TO in the second to last
+      // operand.
+      if (NumOps == 8 &&
+          Desc.getOperandConstraint(6, MCOI::TIED_TO) == 0)
+        return 1;
+      return 0;
+    case 2:
+      // Check for gather. AVX-512 has the second tied operand early. AVX2
+      // has it as the last op.
+      if (NumOps == 9 && Desc.getOperandConstraint(2, MCOI::TIED_TO) == 0 &&
+          (Desc.getOperandConstraint(3, MCOI::TIED_TO) == 1 ||
+           Desc.getOperandConstraint(8, MCOI::TIED_TO) == 1) &&
+          "Instruction with 2 defs isn't gather?")
+        return 2;
+      return 0;
+    }
   }
 
   /// getMemoryOperandNo - The function returns the MCInst operand # for the