[clang] [HLSL][SPIRV] Add -fspv-use-unknown-image-format option (PR #155664)

[Nathan Gauër via cfe-commits]

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@@ -517,14 +517,65 @@ llvm::Type *CommonSPIRTargetCodeGenInfo::getHLSLType(
   return nullptr;
 }
 
+static unsigned
+getImageFormat(const LangOptions &LangOpts,
+               const HLSLAttributedResourceType::Attributes &attributes,
+               llvm::Type *SampledType, QualType Ty, unsigned NumChannels) {
+  // For images with `Sampled` operand equal to 2, there are restrictions on
+  // using the Unknown image format. To avoid these restrictions in common
+  // cases, we guess an image format for them based on the sampled type and the
+  // number of channels. This is intended to match the behaviour of DXC.
+  if (LangOpts.HLSLSpvUseUnknownImageFormat ||
+      attributes.ResourceClass != llvm::dxil::ResourceClass::UAV) {
+    return 0; // Unknown
+  }
+
+  if (SampledType->isIntegerTy(32)) {
+    if (Ty->isSignedIntegerType()) {
+      if (NumChannels == 1)
+        return 24; // R32i
+      if (NumChannels == 2)
+        return 25; // Rg32i
+      if (NumChannels == 4)
+        return 21; // Rgba32i
+    } else {
+      if (NumChannels == 1)
+        return 33; // R32ui
+      if (NumChannels == 2)
+        return 35; // Rg32ui
+      if (NumChannels == 4)
+        return 30; // Rgba32ui
+    }
+  } else if (SampledType->isIntegerTy(64)) {
+    if (NumChannels == 1) {
+      if (Ty->isSignedIntegerType()) {
+        return 41; // R64i
+      }
+      return 40; // R64ui
+    }
+  } else if (SampledType->isFloatTy()) {
+    if (NumChannels == 1)
+      return 3; // R32f
+    if (NumChannels == 2)
+      return 6; // Rg32f
+    if (NumChannels == 4)
+      return 1; // Rgba32f
+  }
+
+  return 0; // Unknown
+}
+
 llvm::Type *CommonSPIRTargetCodeGenInfo::getSPIRVImageTypeFromHLSLResource(
-    const HLSLAttributedResourceType::Attributes &attributes, QualType Ty,
-    CodeGenModule &CGM) const {
+    const HLSLAttributedResourceType::Attributes &attributes,
+    QualType OriginalTy, CodeGenModule &CGM) const {
   llvm::LLVMContext &Ctx = CGM.getLLVMContext();
 
-  Ty = Ty->getCanonicalTypeUnqualified();
-  if (const VectorType *V = dyn_cast<VectorType>(Ty))
+  unsigned NumChannels = 1;
+  QualType Ty = OriginalTy->getCanonicalTypeUnqualified();
+  if (const VectorType *V = dyn_cast<VectorType>(Ty)) {
+    NumChannels = V->getNumElements();
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Keenuts wrote:

The param name could remain Ty no?

https://github.com/llvm/llvm-project/pull/155664