[clang] [llvm] [X86][MC] Added support for -msse2avx option in llvm-mc (PR #96860)

[Fangrui Song via cfe-commits]

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@@ -3745,7 +3749,27 @@ bool X86AsmParser::ParseInstruction(ParseInstructionInfo &Info, StringRef Name,
   return false;
 }
 
+static void replaceSSE2AVXOpcode(MCInst &Inst) {
+  ArrayRef<X86TableEntry> Table{X86SSE2AVXTable};
+  unsigned Opcode = Inst.getOpcode();
+  const auto I = llvm::lower_bound(Table, Opcode);
+  if (I != Table.end() && I->OldOpc == Opcode)
+    Inst.setOpcode(I->NewOpc);
+
+  if (X86::isBLENDVPD(Opcode) || X86::isBLENDVPS(Opcode) ||
+      X86::isPBLENDVB(Opcode)) {
+    unsigned RegNo = Inst.getOperand(2).getReg();
+    Inst.addOperand(MCOperand::createReg(RegNo));
+  }
+}
+
 bool X86AsmParser::processInstruction(MCInst &Inst, const OperandVector &Ops) {
+  // When "-msse2avx" option is enabled replaceSSE2AVXOpcode method will
+  // replace SSE instruction with equivalent AVX instruction using mapping given
+  // in table GET_X86_SSE2AVX_TABLE
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MaskRay wrote:

Agree. `if (X86::isBLENDVPD(Opcode) || X86::isBLENDVPS(Opcode) || ..`  needs a comment.

https://github.com/llvm/llvm-project/pull/96860