Avoid duplicate Alignment decorations (#2537)

The SPIR-V Validator has recently started checking for duplicate
decorations.  This commit fixes duplicate Alignment decorations that
affected the `test/read_image.cl` test.

Alignment decorations have two potential sources during LLVM to SPIR-V
translation: the instruction's alignment property and
`spirv.Decorations` metadata.  Handle both of these through the
`setAlignment` method, so that duplicates can be avoided.

Calling `setAlignment` with different alignments for the same entity
is probably an error, so add an assert.

Contributes to KhronosGroup/SPIRV-LLVM-Translator#2509

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@926ca2ae8497166

Author: svenvh

llvm-spirv/lib/SPIRV/SPIRVWriter.cpp

@@ -1076,7 +1076,7 @@ void LLVMToSPIRVBase::transVectorComputeMetadata(Function *F) {
   }
 }
 
-static void transMetadataDecorations(Metadata *MD, SPIRVEntry *Target);
+static void transMetadataDecorations(Metadata *MD, SPIRVValue *Target);
 
 void LLVMToSPIRVBase::transFPGAFunctionMetadata(SPIRVFunction *BF,
                                                 Function *F) {
@@ -2763,7 +2763,7 @@ void checkIsGlobalVar(SPIRVEntry *E, Decoration Dec) {
                               ErrStr);
 }
 
-static void transMetadataDecorations(Metadata *MD, SPIRVEntry *Target) {
+static void transMetadataDecorations(Metadata *MD, SPIRVValue *Target) {
   SPIRVErrorLog &ErrLog = Target->getErrorLog();
 
   auto *ArgDecoMD = dyn_cast<MDNode>(MD);
@@ -2782,6 +2782,17 @@ static void transMetadataDecorations(Metadata *MD, SPIRVEntry *Target) {
 
     const size_t NumOperands = DecoMD->getNumOperands();
     switch (static_cast<size_t>(DecoKind)) {
+    case DecorationAlignment: {
+      // Handle Alignment via SPIRVValue::setAlignment() to avoid duplicate
+      // Alignment decorations.
+      auto *Alignment =
+          mdconst::dyn_extract<ConstantInt>(DecoMD->getOperand(1));
+      ErrLog.checkError(Alignment, SPIRVEC_InvalidLlvmModule,
+                        "Alignment operand must be an integer.");
+      Target->setAlignment(Alignment->getZExtValue());
+      break;
+    }
+
       ONE_STRING_DECORATION_CASE(MemoryINTEL, spv)
       ONE_STRING_DECORATION_CASE(UserSemantic, spv)
       ONE_INT_DECORATION_CASE(AliasScopeINTEL, spv, SPIRVId)

llvm-spirv/lib/SPIRV/libSPIRV/SPIRVValue.cpp

@@ -51,6 +51,14 @@ void SPIRVValue::setAlignment(SPIRVWord A) {
     eraseDecorate(DecorationAlignment);
     return;
   }
+  SPIRVWord PrevAlignment;
+  if (hasAlignment(&PrevAlignment)) {
+    // Do nothing if the Id already has an Alignment decoration, provided
+    // it matches the new alignment.
+    assert(A == PrevAlignment &&
+           "New alignment does not match existing alignment");
+    return;
+  }
   addDecorate(new SPIRVDecorate(DecorationAlignment, this, A));
   SPIRVDBG(spvdbgs() << "Set alignment " << A << " for obj " << Id << "\n")
 }

llvm-spirv/test/align-duplicate.ll

@@ -0,0 +1,17 @@
+; RUN: llvm-as %s -o %t.bc
+; RUN: llvm-spirv %t.bc -o %t.spv
+; RUN: spirv-val %t.spv
+
+; Test that duplicate align information does not result in SPIR-V validation
+; errors due to duplicate Alignment Decorations.
+
+target datalayout = "e-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024-n8:16:32:64"
+target triple = "spir64-unknown-unknown"
+
+define spir_func void @f() {
+ %res = alloca i16, align 2, !spirv.Decorations !1
+ ret void
+}
+
+!1 = !{!2}
+!2 = !{i32 44, i32 2}