glsl: make minimum struct size = 2, not 1

1-component structs such as "struct foo { float x; }" could get placed at
any position within a register.  This caused some trouble computing the
field offset which assumed all struct objects were placed at R.x.
It would be unusual to hit this case in normal shaders.

(cherry picked from master, commit ca03e881a8d8fa3e36a601238559c20311373633)

diff --git a/src/mesa/shader/slang/slang_codegen.c b/src/mesa/shader/slang/slang_codegen.c
index cc6d714..712f597 100644 (file)
--- a/src/mesa/shader/slang/slang_codegen.c
+++ b/src/mesa/shader/slang/slang_codegen.c
@@ -213,7 +213,14 @@ _slang_sizeof_type_specifier(const slang_type_specifier *spec)
       break;
    case SLANG_SPEC_STRUCT:
       sz = _slang_field_offset(spec, 0); /* special use */
-      if (sz > 4) {
+      if (sz == 1) {
+         /* 1-float structs are actually troublesome to deal with since they
+          * might get placed at R.x, R.y, R.z or R.z.  Return size=2 to
+          * ensure the object is placed at R.x
+          */
+         sz = 2;
+      }
+      else if (sz > 4) {
          sz = (sz + 3) & ~0x3; /* round up to multiple of four */
       }
       break;