Clean up conditional branch codegen.

Should only need to look at whether or not we're branching to our own
merge target. Any other branch needs to emit code in some way.

spirv_glsl.cpp

@@ -12732,87 +12732,37 @@ void CompilerGLSL::branch(BlockID from, uint32_t cond, BlockID true_block, Block
 	auto &from_block = get<SPIRBlock>(from);
 	BlockID merge_block = from_block.merge == SPIRBlock::MergeSelection ? from_block.next_block : BlockID(0);
 
-	// If we branch directly to a selection merge target, we don't need a code path.
-	// This covers both merge out of if () / else () as well as a break for switch blocks.
-	bool true_sub = !is_conditional(true_block);
-	bool false_sub = !is_conditional(false_block);
+	// If we branch directly to our selection merge target, we don't need a code path.
+	bool true_block_needs_code = true_block != merge_block || flush_phi_required(from, true_block);
+	bool false_block_needs_code = false_block != merge_block || flush_phi_required(from, false_block);
 
-	bool true_block_is_selection_merge = true_block == merge_block;
-	bool false_block_is_selection_merge = false_block == merge_block;
+	if (!true_block_needs_code && !false_block_needs_code)
+		return;
 
-	// Can happen if one branch merges to selection branch merge target,
-	// and then the other branches to outer switch merge target.
-	if (!true_sub && !false_sub)
-	{
-		if (true_block_is_selection_merge && false_block_is_selection_merge)
-		{
-			// Useless case (should just be OpBranch), just flush PHI once if needed and execution will continue
-			// at the merge target.
-			if (flush_phi_required(from, merge_block))
-				flush_phi(from, merge_block);
-			return;
-		}
-		else if (true_block_is_selection_merge)
-			false_sub = true;
-		else if (false_block_is_selection_merge)
-			true_sub = true;
-		else
-		{
-			false_sub = true;
-			true_sub = true;
-		}
-	}
+	emit_block_hints(get<SPIRBlock>(from));
 
-	if (true_sub)
+	if (true_block_needs_code)
 	{
-		emit_block_hints(get<SPIRBlock>(from));
 		statement("if (", to_expression(cond), ")");
 		begin_scope();
 		branch(from, true_block);
 		end_scope();
 
-		// If we merge to continue, we handle that explicitly in emit_block_chain(),
-		// so there is no need to branch to it directly here.
-		// break; is required to handle ladder fallthrough cases, so keep that in for now, even
-		// if we could potentially handle it in emit_block_chain().
-		if (false_sub || (!false_block_is_selection_merge && is_continue(false_block)) || is_break(false_block))
+		if (false_block_needs_code)
 		{
 			statement("else");
 			begin_scope();
 			branch(from, false_block);
 			end_scope();
 		}
-		else if (flush_phi_required(from, false_block))
-		{
-			statement("else");
-			begin_scope();
-			flush_phi(from, false_block);
-			end_scope();
-		}
 	}
-	else if (false_sub)
+	else if (false_block_needs_code)
 	{
 		// Only need false path, use negative conditional.
-		emit_block_hints(get<SPIRBlock>(from));
 		statement("if (!", to_enclosed_expression(cond), ")");
 		begin_scope();
 		branch(from, false_block);
 		end_scope();
-
-		if ((!true_block_is_selection_merge && is_continue(true_block)) || is_break(true_block))
-		{
-			statement("else");
-			begin_scope();
-			branch(from, true_block);
-			end_scope();
-		}
-		else if (flush_phi_required(from, true_block))
-		{
-			statement("else");
-			begin_scope();
-			flush_phi(from, true_block);
-			end_scope();
-		}
 	}
 }