<div dir="ltr"><div class="gmail_quote"><div dir="ltr">On Sat, Jul 14, 2018 at 4:26 PM Bas Nieuwenhuizen <<a href="mailto:bas@basnieuwenhuizen.nl">bas@basnieuwenhuizen.nl</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Reinserting code directly before a jump means the block gets split<br>
and merged, removing the original block and replacing it in the<br>
process.<br>
<br>
Hence keeping a pointer to the continue block over a reinsert<br>
causes issues.<br>
<br>
This code changes nir_opt_if to simply look for the new continue<br>
block.<br>
<br>
CC: 18.1 <<a href="mailto:mesa-stable@lists.freedesktop.org" target="_blank">mesa-stable@lists.freedesktop.org</a>><br>
---<br>
src/compiler/nir/nir_opt_if.c | 33 +++++++++++++++++++++++++++------<br>
1 file changed, 27 insertions(+), 6 deletions(-)<br>
<br>
diff --git a/src/compiler/nir/nir_opt_if.c b/src/compiler/nir/nir_opt_if.c<br>
index a52de120ad6..658ff654169 100644<br>
--- a/src/compiler/nir/nir_opt_if.c<br>
+++ b/src/compiler/nir/nir_opt_if.c<br>
@@ -26,6 +26,28 @@<br>
#include "nir_control_flow.h"<br>
#include "nir_loop_analyze.h"<br>
<br>
+/**<br>
+ * Gets the single block that jumps back to the loop header. Already assumes<br>
+ * there is exactly one such block.<br>
+ */<br>
+static nir_block* find_continue_block(nir_loop *loop)<br></blockquote><div><br></div><div>The return type goes on its own line.<br></div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
+{<br>
+ nir_block *header_block = nir_loop_first_block(loop);<br>
+ nir_block *prev_block =<br>
+ nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node));<br>
+<br>
+ assert(header_block->predecessors->entries == 2);<br>
+<br>
+ nir_block *continue_block = NULL;<br>
+ struct set_entry *pred_entry;<br>
+ set_foreach(header_block->predecessors, pred_entry) {<br>
+ if (pred_entry->key != prev_block)<br>
+ continue_block = (void *)pred_entry->key;<br></blockquote><div><br></div><div>Just return right here. No need to keep looping or store continue_block off in a variable.<br></div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
+ }<br>
+<br>
+ return continue_block;<br></blockquote><div><br></div><div>Then this becomes unreachable.</div><div><br></div><div>With those nits fixed,</div><div><br></div><div>Reviewed-by: Jason Ekstrand <<a href="mailto:jason@jlekstrand.net">jason@jlekstrand.net</a>><br></div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
+}<br>
+<br>
/**<br>
* This optimization detects if statements at the tops of loops where the<br>
* condition is a phi node of two constants and moves half of the if to above<br>
@@ -97,12 +119,7 @@ opt_peel_loop_initial_if(nir_loop *loop)<br>
if (header_block->predecessors->entries != 2)<br>
return false;<br>
<br>
- nir_block *continue_block = NULL;<br>
- struct set_entry *pred_entry;<br>
- set_foreach(header_block->predecessors, pred_entry) {<br>
- if (pred_entry->key != prev_block)<br>
- continue_block = (void *)pred_entry->key;<br>
- }<br>
+ nir_block *continue_block = find_continue_block(loop);<br>
<br>
nir_cf_node *if_node = nir_cf_node_next(&header_block->cf_node);<br>
if (!if_node || if_node->type != nir_cf_node_if)<br>
@@ -193,6 +210,10 @@ opt_peel_loop_initial_if(nir_loop *loop)<br>
nir_cf_reinsert(&tmp, nir_before_cf_node(&loop->cf_node));<br>
<br>
nir_cf_reinsert(&header, nir_after_block_before_jump(continue_block));<br>
+<br>
+ /* Get continue block again as the previous reinsert might have removed the block. */<br>
+ continue_block = find_continue_block(loop);<br>
+<br>
nir_cf_extract(&tmp, nir_before_cf_list(continue_list),<br>
nir_after_cf_list(continue_list));<br>
nir_cf_reinsert(&tmp, nir_after_block_before_jump(continue_block));<br>
-- <br>
2.18.0<br>
<br>
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</blockquote></div></div>