fix incorrect variable not assigned error in skslc

Bug: skia:
Change-Id: Id89db8acb0b14024b79b00d98d32f9c10f019537
Reviewed-on: https://skia-review.googlesource.com/18121
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/src/sksl/SkSLCFGGenerator.cpp b/src/sksl/SkSLCFGGenerator.cpp
index 02e4e702a7..71bd37f39a 100644
--- a/src/sksl/SkSLCFGGenerator.cpp
+++ b/src/sksl/SkSLCFGGenerator.cpp
@@ -545,8 +545,13 @@ void CFGGenerator::addStatement(CFG& cfg, std::unique_ptr<Statement>* s) {
             fLoopExits.push(loopExit);
             if (f.fTest) {
                 this->addExpression(cfg, &f.fTest, true);
-                BlockId test = cfg.fCurrent;
-                cfg.addExit(test, loopExit);
+                // this isn't quite right; we should have an exit from here to the loop exit, and
+                // remove the exit from the loop body to the loop exit. Structuring it like this
+                // forces the optimizer to believe that the loop body is always executed at least
+                // once. While not strictly correct, this avoids incorrect "variable not assigned"
+                // errors on variables which are assigned within the loop. The correct solution to
+                // this is to analyze the loop to see whether or not at least one iteration is
+                // guaranteed to happen, but for the time being we take the easy way out.
             }
             cfg.newBlock();
             this->addStatement(cfg, &f.fStatement);
@@ -556,6 +561,7 @@ void CFGGenerator::addStatement(CFG& cfg, std::unique_ptr<Statement>* s) {
                 this->addExpression(cfg, &f.fNext, true);
             }
             cfg.addExit(cfg.fCurrent, loopStart);
+            cfg.addExit(cfg.fCurrent, loopExit);
             fLoopContinues.pop();
             fLoopExits.pop();
             cfg.fCurrent = loopExit;