[tint] Remove Builder::Prepend()

When using this helper to insert multiple instruction, the order of
the instructions becomes reversed, which is unintuitive.

This was only used in one place, and that usage only inserted a single
instruction.

Change-Id: I08dfd71203c78b80457a90eceb5ff72d8c23e109
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/203315
Commit-Queue: James Price <[email protected]>
Reviewed-by: dan sinclair <[email protected]>
Auto-Submit: James Price <[email protected]>

src/tint/lang/core/ir/builder.h

@@ -136,14 +136,6 @@ class Builder {
             /// @param i the instruction to insert
             void operator()(ir::Instruction* i) { block->Append(i); }
         };
-        /// Insertion point method that inserts the instruction to the front of #block
-        struct PrependToBlock {
-            /// The block to insert new instructions to the front of
-            ir::Block* block = nullptr;
-            /// The insertion point function
-            /// @param i the instruction to insert
-            void operator()(ir::Instruction* i) { block->Prepend(i); }
-        };
         /// Insertion point method that inserts the instruction after #after
         struct InsertAfter {
             /// The instruction to insert new instructions after
@@ -165,7 +157,6 @@ class Builder {
     /// A variant of different instruction insertion methods
     using InsertionPoint = std::variant<InsertionPoints::NoInsertion,
                                         InsertionPoints::AppendToBlock,
-                                        InsertionPoints::PrependToBlock,
                                         InsertionPoints::InsertAfter,
                                         InsertionPoints::InsertBefore>;
 
@@ -197,15 +188,6 @@ class Builder {
         cb();
     }
 
-    /// Calls @p cb with the builder prepending to block @p b
-    /// @param b the block to set as the block to prepend to
-    /// @param cb the function to call with the builder prepending to block @p b
-    template <typename FUNCTION>
-    void Prepend(ir::Block* b, FUNCTION&& cb) {
-        TINT_SCOPED_ASSIGNMENT(insertion_point_, InsertionPoints::PrependToBlock{b});
-        cb();
-    }
-
     /// Calls @p cb with the builder inserting after @p ip
     /// @param ip the insertion point for new instructions
     /// @param cb the function to call with the builder inserting new instructions after @p ip

src/tint/lang/spirv/reader/lower/shader_io.cc

@@ -352,9 +352,9 @@ struct State {
             core::ir::Value* result = param;
             if (entry_point && var->Attributes().builtin == core::BuiltinValue::kSampleMask) {
                 // Construct an array from the scalar sample_mask builtin value for entry points.
-                b.Prepend(func->Block(), [&] {  //
-                    result = b.Construct(var->Result(0)->Type()->UnwrapPtr(), param)->Result(0);
-                });
+                auto* construct = b.Construct(var->Result(0)->Type()->UnwrapPtr(), param);
+                func->Block()->Prepend(construct);
+                result = construct->Result(0);
             }
             return result;
         });