Changelog and docs

Changelog.md

@@ -4,7 +4,7 @@ Language Features:
 
 
 Compiler Features:
-
+* Yul Optimizer: Allow replacing the previously hard-coded cleanup sequence by specifying custom steps after a colon delimiter (`:`) in the sequence string.
 
 Bugfixes:
 
@@ -21,7 +21,7 @@ Compiler Features:
  * Yul Optimizer: Simplify the starting offset of zero-length operations to zero.
 
 
-Bugfixes:
+Bugfixes:`````
  * Type Checker: Fix internal compiler error on tuple assignments with invalid left-hand side.
  * Yul IR Code Generation: Fix internal compiler error when accessing the ``.slot`` member of a mapping through a storage reference in inline assembly.
 

docs/internals/optimizer.rst

@@ -329,11 +329,15 @@ the ``--yul-optimizations`` option:
 
 .. code-block:: bash
 
-    solc --optimize --ir-optimized --yul-optimizations 'dhfoD[xarrscLMcCTU]uljmul'
+    solc --optimize --ir-optimized --yul-optimizations 'dhfoD[xarrscLMcCTU]uljmul:fDnTOc'
 
 The sequence inside ``[...]`` will be applied multiple times in a loop until the Yul code
 remains unchanged or until the maximum number of rounds (currently 12) has been reached.
 
+The colon delimiter ``:`` is used to supply a custom clean up sequence in order to replace the
+default (``fDnTOc``) one, which is run after the stack compressor when using the legacy EVM
+code transform.
+
 Available abbreviations are listed in the :ref:`Yul optimizer docs <optimization-step-sequence>`.
 
 Preprocessing

docs/yul.rst

@@ -1250,7 +1250,7 @@ You can override this sequence and supply your own using the ``--yul-optimizatio
 
 .. code-block:: sh
 
-    solc --optimize --ir-optimized --yul-optimizations 'dhfoD[xarrscLMcCTU]uljmul'
+    solc --optimize --ir-optimized --yul-optimizations 'dhfoD[xarrscLMcCTU]uljmul:fDnTOc'
 
 The order of steps is significant and affects the quality of the output.
 Moreover, applying a step may uncover new optimization opportunities for others that were already
@@ -1259,6 +1259,12 @@ By enclosing part of the sequence in square brackets (``[]``) you tell the optim
 apply that part until it no longer improves the size of the resulting assembly.
 You can use brackets multiple times in a single sequence but they cannot be nested.
 
+The colon delimiter (``:``) in the example is used to specify a custom cleanup sequence, which is run after
+the main part of the sequence before the delimiter (and, when using the legacy EVM code transform,
+only *after* the stack compressor). If no such delimiter is present, the default cleanup sequence (``fDnTOc``)
+is run after the supplied sequence.
+
+
 The following optimization steps are available:
 
 ============ ===============================

test/cmdlineTests/yul_optimizer_steps_with_empty_cleanup_sequence/input.sol

@@ -7,6 +7,7 @@ contract C {
         assembly ("memory-safe") {
             let a := 0
             revert(0, a)
+            // Without the cleanup sequence this will not be simplified to ``revert(a, a)``.
         }
     }
 }

test/cmdlineTests/yul_optimizer_steps_with_empty_cleanup_sequence/output

@@ -3,9 +3,9 @@ Optimized IR:
 object "C_8" {
     code {
         {
-            /// @src 0:80:221  "contract C {..."
+            /// @src 0:80:314  "contract C {..."
             mstore(64, memoryguard(0x80))
-            /// @src 0:129:213  "assembly (\"memory-safe\") {..."
+            /// @src 0:129:306  "assembly (\"memory-safe\") {..."
             let usr$a := 0
             revert(0, usr$a)
         }
@@ -14,7 +14,7 @@ object "C_8" {
     object "C_8_deployed" {
         code {
             {
-                /// @src 0:80:221  "contract C {..."
+                /// @src 0:80:314  "contract C {..."
                 mstore(64, memoryguard(0x80))
                 revert(0, 0)
             }

test/cmdlineTests/yul_optimizer_steps_with_empty_optimization_sequence/input.sol

@@ -7,6 +7,7 @@ contract C {
         assembly ("memory-safe") {
             let a := 0
             revert(0, a)
+            // Without the cleanup sequence this will not be simplified to ``revert(a, a)``.
         }
     }
 }

test/cmdlineTests/yul_optimizer_steps_with_empty_optimization_sequence/output

@@ -3,9 +3,9 @@ Optimized IR:
 object "C_8" {
     code {
         {
-            /// @src 0:80:221  "contract C {..."
+            /// @src 0:80:314  "contract C {..."
             mstore(64, memoryguard(0x80))
-            /// @src 0:129:213  "assembly (\"memory-safe\") {..."
+            /// @src 0:129:306  "assembly (\"memory-safe\") {..."
             let usr$a := 0
             revert(0, usr$a)
         }
@@ -14,7 +14,7 @@ object "C_8" {
     object "C_8_deployed" {
         code {
             {
-                /// @src 0:80:221  "contract C {..."
+                /// @src 0:80:314  "contract C {..."
                 mstore(64, memoryguard(0x80))
                 revert(0, 0)
             }