glsl/linker: simplify xfb_offset vs xfb_stride overflow check

Current implementation uses a complicated calculation which relies in
an implicit conversion to check the integral part of 2 division
results.

However, the calculation actually checks that the xfb_offset is
smaller or a multiplier of the xfb_stride. For example, while this is
expected to fail, it actually succeeds:

  "

    ...

    layout(xfb_buffer = 2, xfb_stride = 12) out block3 {
      layout(xfb_offset = 0) vec3 c;
      layout(xfb_offset = 12) vec3 d; // ERROR, requires stride of 24
    };

    ...

  "

Fixes: 2fab85aaea5 ("glsl: add xfb_stride link time validation")
Cc: Timothy Arceri <tarceri@itsqueeze.com>
Signed-off-by: Andres Gomez <agomez@igalia.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

diff --git a/src/compiler/glsl/link_varyings.cpp b/src/compiler/glsl/link_varyings.cpp
index ff225dbcfcc30a4c38cac867e82a1159fbff0424..bf5d7f86f805f7a26fcc513cf7b9539e856772f0 100644 (file)
--- a/src/compiler/glsl/link_varyings.cpp
+++ b/src/compiler/glsl/link_varyings.cpp
@@ -1185,8 +1185,7 @@ tfeedback_decl::store(struct gl_context *ctx, struct gl_shader_program *prog,
          return false;
       }
 
-      if ((this->offset / 4) / info->Buffers[buffer].Stride !=
-          (xfb_offset - 1) / info->Buffers[buffer].Stride) {
+      if (xfb_offset > info->Buffers[buffer].Stride) {
          linker_error(prog, "xfb_offset (%d) overflows xfb_stride (%d) for "
                       "buffer (%d)", xfb_offset * 4,
                       info->Buffers[buffer].Stride * 4, buffer);