[mlir][llvmir][debug] Correctly generate location for phi nodes.

In convertBlockImpl, the debug location is set on the builder before
the op is processed. This results in correct location being given to
corresponding llvm instructions. But same is not done when phi nodes
are created a few lines above. This result is phi nodes getting whatever
the current debug location of the builder is. It can be nothing or in
worst case a stale location. Fixed by calling SetCurrentDebugLocation
before generating phi nodes.

Author: abidh

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

@@ -947,6 +947,8 @@ LogicalResult ModuleTranslation::convertBlockImpl(Block &bb,
       if (!isCompatibleType(wrappedType))
         return emitError(bb.front().getLoc(),
                          "block argument does not have an LLVM type");
+      builder.SetCurrentDebugLocation(
+          debugTranslation->translateLoc(arg.getLoc(), subprogram));
       llvm::Type *type = convertType(wrappedType);
       llvm::PHINode *phi = builder.CreatePHI(type, numPredecessors);
       mapValue(arg, phi);

mlir/test/Target/LLVMIR/llvmir-phi-loc.mlir

@@ -0,0 +1,47 @@
+// RUN: mlir-translate -mlir-to-llvmir %s | FileCheck %s
+
+
+module attributes {} {
+  llvm.func @test(%arg0: !llvm.ptr)  {
+    %0 = llvm.mlir.constant(1 : i64) : i64 loc(#loc2)
+    %1 = llvm.alloca %0 x i32 : (i64) -> !llvm.ptr loc(#loc2)
+    %3 = llvm.mlir.constant(100 : index) : i64 loc(#loc2)
+    %7 = llvm.trunc %0 : i64 to i32 loc(#loc2)
+    llvm.br ^bb1(%7, %3 : i32, i64) loc(#loc2)
+  ^bb1(%8: i32 loc(#loc4), %9: i64 loc(#loc5)):  // 2 preds: ^bb0, ^bb2
+    %10 = llvm.icmp "sgt" %9, %0 : i64 loc(#loc3)
+    llvm.cond_br %10, ^bb2, ^bb3 loc(#loc3)
+  ^bb2:  // pred: ^bb1
+    %13 = llvm.load %1 : !llvm.ptr -> i32 loc(#loc3)
+    %14 = llvm.add %13, %7 : i32 loc(#loc3)
+    %15 = llvm.sub %9, %0 : i64 loc(#loc3)
+    llvm.br ^bb1(%14, %15 : i32, i64) loc(#loc3)
+  ^bb3:  // pred: ^bb1
+    llvm.return loc(#loc3)
+  } loc(#loc6)
+}
+
+#int_ty = #llvm.di_basic_type<tag = DW_TAG_base_type, name = "integer",
+ sizeInBits = 32, encoding = DW_ATE_signed>
+#file = #llvm.di_file<"test.f90" in "">
+#cu = #llvm.di_compile_unit<id = distinct[0]<>,
+ sourceLanguage = DW_LANG_Fortran95, file = #file, isOptimized = false,
+ emissionKind = Full>
+#sp_ty = #llvm.di_subroutine_type<callingConvention = DW_CC_normal,
+ types = #int_ty>
+#sp = #llvm.di_subprogram<id = distinct[1]<>, compileUnit = #cu, scope = #file,
+ name = "test", file = #file, line = 1, scopeLine = 1,
+ subprogramFlags = Definition, type = #sp_ty>
+
+#loc1 = loc("test.f90":1:1)
+#loc2 = loc("test.f90":15:22)
+#loc3 = loc("test.f90":26:3)
+#loc4 = loc("test.f90":8:2)
+#loc5 = loc("test.f90":9:5)
+#loc6 = loc(fused<#sp>[#loc1])
+
+// CHECK-LABEl: define void @test
+// CHECK: phi i32{{.*}}!dbg ![[LOC1:[0-9]+]]
+// CHECK: phi i64{{.*}}!dbg ![[LOC2:[0-9]+]]
+// CHECK: ![[LOC1]] = !DILocation(line: 8, column: 2{{.*}})
+// CHECK: ![[LOC2]] = !DILocation(line: 9, column: 5{{.*}})