From 2476c035ec15d3ee22239ebd1fe10e6e8c1e01e3 Mon Sep 17 00:00:00 2001
From: Tim Foley <tfoley@nvidia.com>
Date: Tue, 18 Jul 2017 14:51:12 -0700
Subject: 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.
---
 source/slang/parser.cpp | 65 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

(limited to 'source/slang/parser.cpp')

diff --git a/source/slang/parser.cpp b/source/slang/parser.cpp
index 1ad0c6b94..b821555a9 100644
--- a/source/slang/parser.cpp
+++ b/source/slang/parser.cpp
@@ -2555,6 +2555,67 @@ namespace Slang
         return isTypeName(parser, name);
     }
 
+    RefPtr<StatementSyntaxNode> parseCompileTimeForStmt(
+        Parser* parser)
+    {
+        RefPtr<ScopeDecl> scopeDecl = new ScopeDecl();
+        RefPtr<CompileTimeForStmt> stmt = new CompileTimeForStmt();
+        stmt->scopeDecl = scopeDecl;
+
+
+        parser->ReadToken("for");
+        parser->ReadToken(TokenType::LParent);
+
+        Token varNameToken = parser->ReadToken(TokenType::Identifier);
+        RefPtr<Variable> varDecl = new Variable();
+        varDecl->Name = varNameToken;
+        varDecl->Position = varNameToken.Position;
+
+        stmt->varDecl = varDecl;
+
+        parser->ReadToken("in");
+        parser->ReadToken("Range");
+        parser->ReadToken(TokenType::LParent);
+
+        RefPtr<ExpressionSyntaxNode> rangeBeginExpr;
+        RefPtr<ExpressionSyntaxNode> rangeEndExpr = parser->ParseArgExpr();
+        if (AdvanceIf(parser, TokenType::Comma))
+        {
+            rangeBeginExpr = rangeEndExpr;
+            rangeEndExpr = parser->ParseArgExpr();
+        }
+
+        stmt->rangeBeginExpr = rangeBeginExpr;
+        stmt->rangeEndExpr = rangeEndExpr;
+
+        parser->ReadToken(TokenType::RParent);
+        parser->ReadToken(TokenType::RParent);
+
+        parser->PushScope(scopeDecl);
+        AddMember(parser->currentScope, varDecl);
+
+        stmt->body = parser->ParseStatement();
+
+        parser->PopScope();
+
+        return stmt;
+    }
+
+    RefPtr<StatementSyntaxNode> parseCompileTimeStmt(
+        Parser* parser)
+    {
+        parser->ReadToken(TokenType::Dollar);
+        if (parser->LookAheadToken("for"))
+        {
+            return parseCompileTimeForStmt(parser);
+        }
+        else
+        {
+            Unexpected(parser);
+            return nullptr;
+        }
+    }
+
     RefPtr<StatementSyntaxNode> Parser::ParseStatement()
     {
         auto modifiers = ParseModifiers(this);
@@ -2591,6 +2652,10 @@ namespace Slang
             statement = ParseCaseStmt(this);
         else if (LookAheadToken("default"))
             statement = ParseDefaultStmt(this);
+        else if (LookAheadToken(TokenType::Dollar))
+        {
+            statement = parseCompileTimeStmt(this);
+        }
         else if (LookAheadToken(TokenType::Identifier))
         {
             // We might be looking at a local declaration, or an
-- 
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