[AMDGPU][MC][GFX11] Correct encoding of VOP3/VOP3_DPP v_cmpx* opcodes

Encode dst=EXEC but allow disassembler accept any dst value.

Differential Revision: https://reviews.llvm.org/D130345

1 files changed, 16 insertions, 0 deletions

diff --git a/llvm/lib/Target/AMDGPU/MCTargetDesc/SIMCCodeEmitter.cpp b/llvm/lib/Target/AMDGPU/MCTargetDesc/SIMCCodeEmitter.cpp
index e093d78..d9d7d4e 100644
--- a/llvm/lib/Target/AMDGPU/MCTargetDesc/SIMCCodeEmitter.cpp
+++ b/llvm/lib/Target/AMDGPU/MCTargetDesc/SIMCCodeEmitter.cpp
@@ -309,6 +309,11 @@ uint64_t SIMCCodeEmitter::getImplicitOpSelHiEncoding(int Opcode) const {
   return OP_SEL_HI_0 | OP_SEL_HI_1 | OP_SEL_HI_2;
 }
 
+static bool isVCMPX64(const MCInstrDesc &Desc) {
+  return (Desc.TSFlags & SIInstrFlags::VOP3) &&
+         Desc.hasImplicitDefOfPhysReg(AMDGPU::EXEC);
+}
+
 void SIMCCodeEmitter::encodeInstruction(const MCInst &MI, raw_ostream &OS,
                                         SmallVectorImpl<MCFixup> &Fixups,
                                         const MCSubtargetInfo &STI) const {
@@ -326,6 +331,17 @@ void SIMCCodeEmitter::encodeInstruction(const MCInst &MI, raw_ostream &OS,
     Encoding |= getImplicitOpSelHiEncoding(Opcode);
   }
 
+  // GFX11 v_cmpx opcodes promoted to VOP3 have implied dst=EXEC.
+  // Documentation requires dst to be encoded as EXEC (0x7E),
+  // but it looks like the actual value encoded for dst operand
+  // is ignored by HW. It was decided to define dst as "do not care"
+  // in td files to allow disassembler accept any dst value.
+  // However, dst is encoded as EXEC for compatibility with SP3.
+  if (AMDGPU::isGFX11Plus(STI) && isVCMPX64(Desc)) {
+    assert((Encoding & 0xFF) == 0);
+    Encoding |= MRI.getEncodingValue(AMDGPU::EXEC_LO);
+  }
+
   for (unsigned i = 0; i < bytes; i++) {
     OS.write((uint8_t)Encoding.extractBitsAsZExtValue(8, 8 * i));
   }