[SPIRV] Allow multiple FuncParamAttr decoration on the same id. (llvm#166782)

According to SPIR-V spec:

> It is invalid to decorate any given id or structure member more than
one time with the same
[decoration](https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#Decoration),
unless explicitly allowed below for a specific decoration.

`FuncParamAttr` explicitly allows multiple uses of the decoration on the
same id, so this patch honors it.

Author: maarquitos14

llvm/lib/Target/SPIRV/SPIRVModuleAnalysis.cpp

@@ -249,17 +249,18 @@ static InstrSignature instrToSignature(const MachineInstr &MI,
   InstrSignature Signature{MI.getOpcode()};
   for (unsigned i = 0; i < MI.getNumOperands(); ++i) {
     // The only decorations that can be applied more than once to a given <id>
-    // or structure member are UserSemantic(5635), CacheControlLoadINTEL (6442),
-    // and CacheControlStoreINTEL (6443). For all the rest of decorations, we
-    // will only add to the signature the Opcode, the id to which it applies,
-    // and the decoration id, disregarding any decoration flags. This will
-    // ensure that any subsequent decoration with the same id will be deemed as
-    // a duplicate. Then, at the call site, we will be able to handle duplicates
-    // in the best way.
+    // or structure member are FuncParamAttr (38), UserSemantic (5635),
+    // CacheControlLoadINTEL (6442), and CacheControlStoreINTEL (6443). For all
+    // the rest of decorations, we will only add to the signature the Opcode,
+    // the id to which it applies, and the decoration id, disregarding any
+    // decoration flags. This will ensure that any subsequent decoration with
+    // the same id will be deemed as a duplicate. Then, at the call site, we
+    // will be able to handle duplicates in the best way.
     unsigned Opcode = MI.getOpcode();
     if ((Opcode == SPIRV::OpDecorate) && i >= 2) {
       unsigned DecorationID = MI.getOperand(1).getImm();
-      if (DecorationID != SPIRV::Decoration::UserSemantic &&
+      if (DecorationID != SPIRV::Decoration::FuncParamAttr &&
+          DecorationID != SPIRV::Decoration::UserSemantic &&
           DecorationID != SPIRV::Decoration::CacheControlLoadINTEL &&
           DecorationID != SPIRV::Decoration::CacheControlStoreINTEL)
         continue;

llvm/test/CodeGen/SPIRV/spirv_param_decorations_quals.ll

@@ -7,9 +7,11 @@ entry:
 
 ; CHECK-SPIRV: OpDecorate %[[#PId:]] Volatile
 ; CHECK-SPIRV: OpDecorate %[[#PId]] FuncParamAttr NoAlias
+; CHECK-SPIRV: OpDecorate %[[#PId]] FuncParamAttr NoWrite
 ; CHECK-SPIRV: %[[#PId]] = OpFunctionParameter %[[#]]
 
 !7 = !{!"volatile"}
 !8 = !{i32 38, i32 4} ; FuncParamAttr NoAlias
-!9 = !{!8}
+!11 = !{i32 38, i32 6} ; FuncParamAttr NoWrite
+!9 = !{!8, !11}
 !10 = !{!9}