Merge remote-tracking branch 'origin/topic/bbannier/fold_while'

CHANGES

@@ -1,3 +1,11 @@
+1.10.0-dev.158 | 2024-03-01 18:10:49 +0100
+
+  * Simplify `while` loops over constant conditions. (Benjamin Bannier, Corelight)
+
+    While loops with constant conditions are unlikely to occur in code
+    generated by us, but could appear in user code. Cleaning them up is
+    simple and cheap, so this patch implements a pass which simplifies them.
+
 1.10.0-dev.156 | 2024-02-27 17:44:22 +0100
 
   * GH-1624: Enable optimizations when running `spicy-build`. (Benjamin Bannier, Corelight)

VERSION

@@ -1 +1 @@
-1.10.0-dev.156
+1.10.0-dev.158

hilti/toolchain/src/compiler/optimizer.cc

@@ -12,17 +12,20 @@
 #include <hilti/ast/builder/expression.h>
 #include <hilti/ast/ctors/default.h>
 #include <hilti/ast/declaration.h>
+#include <hilti/ast/declarations/constant.h>
 #include <hilti/ast/declarations/function.h>
 #include <hilti/ast/declarations/imported-module.h>
 #include <hilti/ast/detail/visitor.h>
 #include <hilti/ast/expressions/ctor.h>
+#include <hilti/ast/expressions/id.h>
 #include <hilti/ast/expressions/logical-and.h>
 #include <hilti/ast/expressions/logical-not.h>
 #include <hilti/ast/expressions/logical-or.h>
 #include <hilti/ast/expressions/ternary.h>
 #include <hilti/ast/node.h>
 #include <hilti/ast/scope-lookup.h>
 #include <hilti/ast/statements/block.h>
+#include <hilti/ast/statements/while.h>
 #include <hilti/ast/type.h>
 #include <hilti/ast/types/bool.h>
 #include <hilti/ast/types/enum.h>
@@ -898,6 +901,41 @@ struct ConstantFoldingVisitor : OptimizerVisitor, visitor::PreOrder<bool, Consta
 
         return false;
     }
+
+    bool operator()(const statement::While& x, position_t p) {
+        switch ( _stage ) {
+            case Stage::COLLECT:
+            case Stage::PRUNE_DECLS: return false;
+            case Stage::PRUNE_USES: {
+                const auto& cond = x.condition();
+                if ( ! cond )
+                    return false;
+
+                const auto val = tryAsBoolLiteral(*cond);
+                if ( ! val )
+                    return false;
+
+                // If the `while` condition is true we never run the `else` block.
+                if ( *val && x.else_() ) {
+                    // Remove child for `else`.
+                    p.node.as<statement::While>().children()[3] = node::none;
+                    return true;
+                }
+                // If the `while` condition is false we never enter the loop, and
+                // run either the `else` block if it is present or nothing.
+                else if ( ! *val ) {
+                    if ( const auto& else_ = x.else_() )
+                        replaceNode(p, else_->_clone());
+                    else
+                        removeNode(p);
+
+                    return true;
+                }
+
+                return false;
+            }
+        }
+    }
 };
 
 // This visitor collects requirement attributes in the AST and toggles unused features.

tests/Baseline/hilti.optimization.const/noopt.hlt

@@ -47,4 +47,28 @@ True;
 t ? 1 : 0;
 f ? 0 : 1;
 
+while ( False ) {
+}
+
+
+while ( False ) {
+    False;
+}
+else {
+    True;
+}
+
+
+while ( True ) {
+}
+
+
+while ( True ) {
+    True;
+}
+else {
+    False;
+}
+
+
 }

tests/Baseline/hilti.optimization.const/opt.hlt

@@ -29,5 +29,17 @@ False;
 True;
 1;
 1;
+{
+    True;
+}
+
+while ( True ) {
+}
+
+
+while ( True ) {
+    True;
+}
+
 
 }

tests/hilti/optimization/const.hlt

@@ -52,4 +52,21 @@ f && f;
 t ? 1: 0;
 f ? 0: 1;
 
+# While loops over constants.
+while (False) {}
+
+while (False) {
+    False;
+} else {
+    True;
+}
+
+while (True) {}
+
+while (True) {
+    True;
+} else {
+    False;
+}
+
 }