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/lower.cpp | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

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

diff --git a/source/slang/lower.cpp b/source/slang/lower.cpp
index bbbfe724b..127ef75ca 100644
--- a/source/slang/lower.cpp
+++ b/source/slang/lower.cpp
@@ -1628,6 +1628,41 @@ struct LoweringVisitor
         lowerForStmtCommon(new UnscopedForStmt(), stmt);
     }
 
+    void visitCompileTimeForStmt(CompileTimeForStmt* stmt)
+    {
+        // We can either lower this here, so that emit logic doesn't have to deal with it,
+        // or else just translate it and then let emit deal with it.
+        //
+        // The right answer is really to lower it here, I guess.
+
+        auto rangeBeginVal = GetIntVal(stmt->rangeBeginVal);
+        auto rangeEndVal = GetIntVal(stmt->rangeEndVal);
+
+        if (rangeBeginVal >= rangeEndVal)
+            return;
+
+        auto varDecl = stmt->varDecl;
+
+        auto varType = lowerType(varDecl->Type);
+
+        for (IntegerLiteralValue ii = rangeBeginVal; ii < rangeEndVal; ++ii)
+        {
+            RefPtr<ConstantExpressionSyntaxNode> constExpr = new ConstantExpressionSyntaxNode();
+            constExpr->Type.type = varType.type;
+            constExpr->ConstType = ConstantExpressionSyntaxNode::ConstantType::Int;
+            constExpr->integerValue = ii;
+
+            RefPtr<VaryingTupleVarDecl> loweredVarDecl = new VaryingTupleVarDecl();
+            loweredVarDecl->Position = varDecl->Position;
+            loweredVarDecl->Type = varType;
+            loweredVarDecl->Expr = constExpr;
+
+            shared->loweredDecls[varDecl] = loweredVarDecl;
+
+            lowerStmtImpl(stmt->body);
+        }
+    }
+
     void visitWhileStatementSyntaxNode(WhileStatementSyntaxNode* stmt)
     {
         RefPtr<WhileStatementSyntaxNode> loweredStmt = new WhileStatementSyntaxNode();
-- 
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