WGSL: fix do-while when body has continue

If the body of the do while had a "continue" it would
skip over the evaluation of the loop condition and
potentially loop forever.

Change to use the special WGSL "continuing" statement,
which goes at the end of a loop body and always executes,
even if there is an earlier "continue".

Bug: angleproject:42267100
Change-Id: I4ac73e6abcb12e0ff395b83dc5666ac1870724e9
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/7003772
Reviewed-by: Liza Burakova <liza@chromium.org>
Commit-Queue: Matthew Denton <mpdenton@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>

Author: mdenton8

src/compiler/translator/wgsl/TranslatorWGSL.cpp

@@ -2367,6 +2367,23 @@ bool OutputWGSLTraverser::emulateDoWhileLoop(TIntermLoop *loopNode)
 {
     ASSERT(loopNode->getType() == TLoopType::ELoopDoWhile);
 
+    // Emulate do-while with an infinite loop and a WGSL-special "continuing" and "break-if"
+    // statement.
+    //
+    // Example GLSL:
+    // do {
+    //    // Loop body, which might contain 'continue'
+    // } while(condition)
+    //
+    // Becomes WGSL:
+    // loop {
+    //   // Loop body, which might contain 'continue'
+
+    //   continuing {
+    //     break if !condition;
+    //   }
+    // }
+
     TIntermNode *initNode  = loopNode->getInit();
     TIntermTyped *condNode = loopNode->getCondition();
     TIntermTyped *exprNode = loopNode->getExpression();
@@ -2377,13 +2394,20 @@ bool OutputWGSLTraverser::emulateDoWhileLoop(TIntermLoop *loopNode)
     // Write an infinite loop.
     mSink << "loop {\n";
     mIndentLevel++;
+    // The loop body may contain a "continue" branch.
     loopNode->getBody()->traverse(this);
     mSink << "\n";
     emitIndentation();
     // At the end of the loop, break if the loop condition dos not still hold.
-    mSink << "if (!(";
+    mSink << "continuing {\n";
+    mIndentLevel++;
+    emitIndentation();
+    mSink << "break if !(";
     condNode->traverse(this);
-    mSink << ") { break; }\n";
+    mSink << ");\n";
+    mIndentLevel--;
+    emitIndentation();
+    mSink << "}\n";
     mIndentLevel--;
     emitIndentation();
     mSink << "}";

src/tests/compiler_tests/WGSLOutput_test.cpp

@@ -646,7 +646,9 @@ fn _uwhileLoopDemo()
     {
       (_ui)++;
     }
-    if (!((_ui) < (5i)) { break; }
+    continuing {
+      break if !((_ui) < (5i));
+    }
   }
 }