shaderir: Add Stmt.ForVarIndex

Updates #1230

internal/shaderir/glsl.go

@@ -364,8 +364,7 @@ func (p *Program) glslBlock(topBlock, block *Block, level int, localVarIndex int
 			}
 			lines = append(lines, fmt.Sprintf("%s}", idt))
 		case For:
-			v := localVarIndex
-			localVarIndex++
+			v := s.ForVarIndex
 			var delta string
 			switch s.ForDelta {
 			case 0:

internal/shaderir/ir_test.go

@@ -64,10 +64,11 @@ func ifStmt(cond Expr, block Block, elseBlock Block) Stmt {
 	}
 }
 
-func forStmt(init, end int, op Op, delta int, block Block) Stmt {
+func forStmt(index, init, end int, op Op, delta int, block Block) Stmt {
 	return Stmt{
 		Type:        For,
 		Blocks:      []Block{block},
+		ForVarIndex: index,
 		ForInit:     init,
 		ForEnd:      end,
 		ForOp:       op,
@@ -592,6 +593,7 @@ varying vec3 V0;`,
 						Block: block(
 							nil,
 							forStmt(
+								3,
 								0,
 								100,
 								LessThanOp,

internal/shaderir/program.go

@@ -67,6 +67,7 @@ type Stmt struct {
 	Type        StmtType
 	Exprs       []Expr
 	Blocks      []Block
+	ForVarIndex int
 	ForInit     int
 	ForEnd      int
 	ForOp       Op