Lower constant expressions inside metadata operands

It is possible that instruction has metadata operand which is actually
is a constant expression which should be lowered, for example constant
expression metadata can appear as operand of debug instruction.

lib/SPIRV/SPIRVLowerConstExpr.cpp

@@ -170,8 +170,21 @@ void SPIRVLowerConstExpr::visit(Module *M) {
           }
           II->replaceUsesOfWith(Op, Repl);
           WorkList.splice(WorkList.begin(), ReplList);
-        } else if (auto CE = dyn_cast<ConstantExpr>(Op))
+        } else if (auto CE = dyn_cast<ConstantExpr>(Op)) {
           WorkList.push_front(cast<Instruction>(LowerOp(CE)));
+        } else if (auto MDAsVal = dyn_cast<MetadataAsValue>(Op)) {
+          Metadata *MD = MDAsVal->getMetadata();
+          if (auto ConstMD = dyn_cast<ConstantAsMetadata>(MD)) {
+            Constant *C = ConstMD->getValue();
+            if (auto CE = dyn_cast<ConstantExpr>(C)) {
+              Value *RepInst = LowerOp(CE);
+              Metadata *RepMD = ValueAsMetadata::get(RepInst);
+              Value *RepMDVal = MetadataAsValue::get(M->getContext(), RepMD);
+              II->setOperand(OI, RepMDVal);
+              WorkList.push_front(cast<Instruction>(RepInst));
+            }
+          }
+        }
       }
     }
   }

test/lshr-constexpr.ll

@@ -0,0 +1,65 @@
+; RUN: llvm-as %s -o %t.bc
+; RUN: llvm-spirv %t.bc -o %t.spv
+; RUN: llvm-spirv -r %t.spv -o %from-spirv.bc
+; RUN: llvm-dis %from-spirv.bc -o - | FileCheck %s --check-prefix=CHECK-LLVM
+; RUN: llvm-spirv --to-text %t.spv -o - | FileCheck %s --check-prefix=CHECK-SPIRV
+
+; TODO: spirv-val command is not presented here because it fails with error:
+; line 29: Invalid source language operand: 12 which is not related to
+; functionality that is being checked in this test.
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "spir64-unknown-unknown"
+
+; CHECK-SPIRV: TypeInt [[type_int32:[0-9]+]] 32 0
+; CHECK-SPIRV: TypeInt [[type_int64:[0-9]+]] 64 0
+; CHECK-SPIRV: Constant [[type_int32]] [[const1:[0-9]+]] 1
+; CHECK-SPIRV: Constant [[type_int64]] [[const32:[0-9]+]] 32 0
+; CHECK-SPIRV: TypeVector [[type_vec:[0-9]+]] [[type_int32]] 2
+; CHECK-SPIRV: ConstantComposite [[type_vec]] [[vec_const:[0-9]+]] [[const1]] [[const1]]
+
+; CHECK-SPIRV: Bitcast [[type_int64]] [[bitcast_res:[0-9]+]] [[vec_const]]
+; CHECK-SPIRV: ShiftRightLogical [[type_int64]] [[shift_res:[0-9]+]] [[bitcast_res]] [[const32]]
+; CHECK-SPIRV: DebugValue {{[0-9]+}} [[shift_res]]
+
+; Function Attrs: nounwind ssp uwtable
+define void @foo() #0 !dbg !4 {
+entry:
+  tail call void @llvm.dbg.value(metadata i64 lshr (i64 bitcast (<2 x i32> <i32 1, i32 1> to i64), i64 32), metadata !12, metadata !17) #3, !dbg !18
+  ret void, !dbg !20
+; CHECK-LLVM: %[[bitcast:[0-9]+]] = bitcast <2 x i32> <i32 1, i32 1> to i64
+; CHECK-LLVM: %[[shift:[0-9]+]] = lshr i64 %[[bitcast]], 32
+; CHECK-LLVM: call void @llvm.dbg.value(metadata i64 %[[shift]], metadata !{{[0-9]+}}, metadata !DIExpression()), !dbg !{{[0-9]+}}
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, metadata, metadata) #2
+
+attributes #0 = { nounwind ssp uwtable  }
+attributes #2 = { nounwind readnone }
+attributes #3 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!13, !14, !15}
+!llvm.ident = !{!16}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.7.0 (trunk 235110) (llvm/trunk 235108)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !2, globals: !2, imports: !2)
+!1 = !DIFile(filename: "t.c", directory: "/path/to/dir")
+!2 = !{}
+!4 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 3, type: !5, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !0, retainedNodes: !2)
+!5 = !DISubroutineType(types: !6)
+!6 = !{null}
+!7 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 2, type: !8, isLocal: true, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: true, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !10}
+!10 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !1, line: 2, type: !10)
+!13 = !{i32 2, !"Dwarf Version", i32 2}
+!14 = !{i32 2, !"Debug Info Version", i32 3}
+!15 = !{i32 1, !"PIC Level", i32 2}
+!16 = !{!"clang version 3.7.0 (trunk 235110) (llvm/trunk 235108)"}
+!17 = !DIExpression()
+!18 = !DILocation(line: 2, column: 52, scope: !7, inlinedAt: !19)
+!19 = distinct !DILocation(line: 4, column: 3, scope: !4)
+!20 = !DILocation(line: 6, column: 1, scope: !4)