[llvm] [SPIR-V] Use `OpImageFetch` instead of `OpImageRead` when loading from read-only `Buffer` resource. (PR #163626)

[Lucie Choi via llvm-commits]

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@@ -3633,27 +3633,32 @@ bool SPIRVInstructionSelector::selectReadImageIntrinsic(
   DebugLoc Loc = I.getDebugLoc();
   MachineInstr &Pos = I;
 
-  return generateImageRead(ResVReg, ResType, NewImageReg, IdxReg, Loc, Pos);
+  return generateImageReadOrFetch(ResVReg, ResType, NewImageReg, IdxReg, Loc,
+                                  Pos);
 }
 
-bool SPIRVInstructionSelector::generateImageRead(Register &ResVReg,
-                                                 const SPIRVType *ResType,
-                                                 Register ImageReg,
-                                                 Register IdxReg, DebugLoc Loc,
-                                                 MachineInstr &Pos) const {
+bool SPIRVInstructionSelector::generateImageReadOrFetch(
+    Register &ResVReg, const SPIRVType *ResType, Register ImageReg,
+    Register IdxReg, DebugLoc Loc, MachineInstr &Pos) const {
   SPIRVType *ImageType = GR.getSPIRVTypeForVReg(ImageReg);
   assert(ImageType && ImageType->getOpcode() == SPIRV::OpTypeImage &&
          "ImageReg is not an image type.");
+
   bool IsSignedInteger =
       sampledTypeIsSignedInteger(GR.getTypeForSPIRVType(ImageType));
+  // Check if the "sampled" operand of the image type is 2.
+  auto SampledOp = ImageType->getOperand(6);
+  bool IsFetch = (SampledOp.getImm() != 2);
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luciechoi wrote:

Thanks for catching! Updated.

https://github.com/llvm/llvm-project/pull/163626