Bug 94297

Although this is technically a regression, I don't really consider it critical.

The problem is that the GLSL compiler checks for barrier being in an allowed position too late.  We passed this test previously because our switch statements always generated lousy code (pointless loops that ran for a single iteration). Now, we don't.

Also, the result of this bug is that we accept programs that we should reject according to the rules.  We also happen to compile them and do what the author intended.  So it's a portability problem (apps written against our driver may work on our driver but not work on other drivers), but not going to break any valid apps.

Removing from the 12.0 release tracker.

The CI system says that this commit fixed the test, which is somewhat surprising.

commit 943b69cddd2ae90e0b0fcab2dff4a7eea81bb3cc
Author: Kenneth Graunke <kenneth@whitecape.org>
Date:   Tue Nov 11 22:32:27 2014 -0800

    glsl: Delete linker stuff relating to built-in functions.

Ken, could you confirm?

The actual commit was earlier in the series:

1617f59bc675d6e44d16ab56d95e910d2e2c8f4e
glsl: Check TCS barrier restrictions at ast_to_hir time, not link time.

We want to check prior to optimization - otherwise we might fail to
detect cases where barrier() is in control flow which is always taken
(and therefore gets optimized away).

We don't currently loop unroll if there are function calls inside;
otherwise we might have a problem detecting barrier() in loops that
get unrolled as well.

Tapani's switch handling code adds a loop around switch statements, so
even with the mess of if ladders, we'll properly reject it.

Enforcing these rules at compile time makes more sense more sense than
link time.  Doing it at ast-to-hir time (rather than as an IR pass)
allows us to emit an error message with proper line numbers.
(Otherwise, I would have preferred the IR pass...)

Fixes spec/arb_tessellation_shader/compiler/barrier-switch-always.tesc.

Mark is right.  I had to rewrite the barrier error enforcement code as part of that series - the old approach worked on ir_calls, which is incompatible with the idea of inlining all calls right off the bat.  So while I was at it, I fixed this simple bug.