Add a compile-time loop construct to Slang

The basic syntax is:

    $for(i in Range(0,99))
    {
       /* stuff goes here */
    }

Note that the exact form is very restrictive. All that you are allowed to change is `i`, `0`, `99` or `/* stuff goes here */`.

As a tiny bit of syntax sugar, the following should work:

    $for(i in Range(99))
    {
       /* stuff goes here */
    }

Note that the range given is half-open (C++ iterator `[begin,end)` style).
Both the beginning and end of the range must be compile-time constant expressions that Slang knows how to constant-fold.

The implementation will basically generate code for `/* stuff goes here */` N times, once for each value in the half-open range.
Each time, the variable `i` will be replaced with a different compile-time-constant expression.

While I was working on a test case for this, I also found that our build of glslang had an issue with resource limits, so I fixed that.
Clients will need to build a new glslang to use the fix.

1 files changed, 42 insertions, 0 deletions

diff --git a/source/slang/check.cpp b/source/slang/check.cpp
index 1c1c6d5d3..26d28d495 100644
--- a/source/slang/check.cpp
+++ b/source/slang/check.cpp
@@ -1735,6 +1735,48 @@ namespace Slang
 
             PopOuterStmt(stmt);
         }
+
+        RefPtr<ExpressionSyntaxNode> checkExpressionAndExpectIntegerConstant(RefPtr<ExpressionSyntaxNode> expr, RefPtr<IntVal>* outIntVal)
+        {
+            expr = CheckExpr(expr);
+            auto intVal = CheckIntegerConstantExpression(expr);
+            if (outIntVal)
+                *outIntVal = intVal;
+            return expr;
+        }
+
+        void visitCompileTimeForStmt(CompileTimeForStmt* stmt)
+        {
+            PushOuterStmt(stmt);
+
+            stmt->varDecl->Type.type = ExpressionType::GetInt();
+            addModifier(stmt->varDecl, new ConstModifier());
+
+            RefPtr<IntVal> rangeBeginVal;
+            RefPtr<IntVal> rangeEndVal;
+
+            if (stmt->rangeBeginExpr)
+            {
+                stmt->rangeBeginExpr = checkExpressionAndExpectIntegerConstant(stmt->rangeBeginExpr, &rangeBeginVal);
+            }
+            else
+            {
+                RefPtr<ConstantIntVal> rangeBeginConst = new ConstantIntVal();
+                rangeBeginConst->value = 0;
+                rangeBeginVal = rangeBeginConst;
+            }
+
+            stmt->rangeEndExpr = checkExpressionAndExpectIntegerConstant(stmt->rangeEndExpr, &rangeEndVal);
+
+            stmt->rangeBeginVal = rangeBeginVal;
+            stmt->rangeEndVal = rangeEndVal;
+
+            checkStmt(stmt->body);
+
+
+            PopOuterStmt(stmt);
+        }
+
         void visitSwitchStmt(SwitchStmt* stmt)
         {
             PushOuterStmt(stmt);