1 files changed, 26 insertions, 1 deletions
diff --git a/llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp b/llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp
index 1885b5958e8..9e2957e9c1a 100644
--- a/llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp
+++ b/llvm/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp
@@ -1053,6 +1053,7 @@ private:
   bool validateEarlyClobberLimitations(const MCInst &Inst);
   bool validateIntClampSupported(const MCInst &Inst);
   bool validateMIMGAtomicDMask(const MCInst &Inst);
+  bool validateMIMGGatherDMask(const MCInst &Inst);
   bool validateMIMGDataSize(const MCInst &Inst);
   bool validateMIMGR128(const MCInst &Inst);
   bool validateMIMGD16(const MCInst &Inst);
@@ -2299,7 +2300,7 @@ bool AMDGPUAsmParser::validateMIMGDataSize(const MCInst &Inst) {
   if ((Desc.TSFlags & SIInstrFlags::MIMG) == 0)
     return true;
 
-  // Gather4 instructions seem to have special rules not described in spec.
+  // Gather4 instructions do not need validation: dst size is hardcoded.
   if (Desc.TSFlags & SIInstrFlags::Gather4)
     return true;
 
@@ -2345,6 +2346,25 @@ bool AMDGPUAsmParser::validateMIMGAtomicDMask(const MCInst &Inst) {
   return DMask == 0x1 || DMask == 0x3 || DMask == 0xf;
 }
 
+bool AMDGPUAsmParser::validateMIMGGatherDMask(const MCInst &Inst) {
+
+  const unsigned Opc = Inst.getOpcode();
+  const MCInstrDesc &Desc = MII.get(Opc);
+
+  if ((Desc.TSFlags & SIInstrFlags::Gather4) == 0)
+    return true;
+
+  int DMaskIdx = AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::dmask);
+  unsigned DMask = Inst.getOperand(DMaskIdx).getImm() & 0xf;
+
+  // GATHER4 instructions use dmask in a different fashion compared to
+  // other MIMG instructions. The only useful DMASK values are
+  // 1=red, 2=green, 4=blue, 8=alpha. (e.g. 1 returns
+  // (red,red,red,red) etc.) The ISA document doesn't mention
+  // this.
+  return DMask == 0x1 || DMask == 0x2 || DMask == 0x4 || DMask == 0x8;
+}
+
 bool AMDGPUAsmParser::validateMIMGR128(const MCInst &Inst) {
 
   const unsigned Opc = Inst.getOpcode();
@@ -2412,6 +2432,11 @@ bool AMDGPUAsmParser::validateInstruction(const MCInst &Inst,
       "invalid atomic image dmask");
     return false;
   }
+  if (!validateMIMGGatherDMask(Inst)) {
+    Error(IDLoc,
+      "invalid image_gather dmask: only one bit must be set");
+    return false;
+  }
 
   return true;
 }