tgsi/scan: add support to figure out max nesting depth

Sometimes a useful thing for compilers (or, for example, tgsi_to_nir) to
know.  And pretty trivial for scan to figure this out for us.

Signed-off-by: Rob Clark <robclark@freedesktop.org>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/gallium/auxiliary/tgsi/tgsi_scan.c

@@ -56,6 +56,7 @@ tgsi_scan_shader(const struct tgsi_token *tokens,
 {
    uint procType, i;
    struct tgsi_parse_context parse;
+   unsigned current_depth = 0;
 
    memset(info, 0, sizeof(*info));
    for (i = 0; i < TGSI_FILE_COUNT; i++)
@@ -100,6 +101,21 @@ tgsi_scan_shader(const struct tgsi_token *tokens,
             assert(fullinst->Instruction.Opcode < TGSI_OPCODE_LAST);
             info->opcode_count[fullinst->Instruction.Opcode]++;
 
+            switch (fullinst->Instruction.Opcode) {
+            case TGSI_OPCODE_IF:
+            case TGSI_OPCODE_UIF:
+            case TGSI_OPCODE_BGNLOOP:
+               current_depth++;
+               info->max_depth = MAX2(info->max_depth, current_depth);
+               break;
+            case TGSI_OPCODE_ENDIF:
+            case TGSI_OPCODE_ENDLOOP:
+               current_depth--;
+               break;
+            default:
+               break;
+            }
+
             if (fullinst->Instruction.Opcode >= TGSI_OPCODE_F2D &&
                 fullinst->Instruction.Opcode <= TGSI_OPCODE_DSSG)
                info->uses_doubles = true;

src/gallium/auxiliary/tgsi/tgsi_scan.h

@@ -113,6 +113,11 @@ struct tgsi_shader_info
    unsigned indirect_files_written;
 
    unsigned properties[TGSI_PROPERTY_COUNT]; /* index with TGSI_PROPERTY_ */
+
+   /**
+    * Max nesting limit of loops/if's
+    */
+   unsigned max_depth;
 };
 
 extern void