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authorChristoph Bumiller <e0425955@student.tuwien.ac.at>2014-09-06 01:36:48 +0200
committerIlia Mirkin <imirkin@alum.mit.edu>2014-09-05 23:08:24 -0400
commitca9ab05d45ebf407485af2daa3742b897ff99162 (patch)
tree73b03cedfad114dab23f12c6ad9dfdeebec5aa72 /src/gallium/drivers
parentb9f9e3ce03dbd8d044a72a00e1e8856a500b5f72 (diff)
nvc0/ir: clarify recursion fix to finding first tex uses
This is a simple shader for reproducing the case mentioned: FRAG DCL IN[0], GENERIC[0], PERSPECTIVE DCL OUT[0], COLOR DCL SAMP[0] DCL CONST[0] DCL TEMP[0..1], LOCAL IMM[0] FLT32 { 0.0000, -1.0000, 1.0000, 0.0000} 0: MOV TEMP[0].x, CONST[0].wwww 1: MOV TEMP[1].x, CONST[0].wwww 2: BGNLOOP 3: IF TEMP[0].xxxx 4: BRK 5: ENDIF 6: ADD TEMP[0].x, TEMP[0], IMM[0].zzzz 7: IF CONST[0].xxxx 8: TEX TEMP[1].x, CONST[0], SAMP[0], 2D 9: ENDIF 10: IF CONST[0].zzzz 11: MOV TEMP[1].x, CONST[0].zzzz 12: ENDIF 13: ENDLOOP 14: MOV OUT[0], TEMP[1].xxxx 15: END Cc: "10.2 10.3" <mesa-stable@lists.freedesktop.org> Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Diffstat (limited to 'src/gallium/drivers')
-rw-r--r--src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp16
1 files changed, 7 insertions, 9 deletions
diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
index 92f9a156f7c..b3e1e69b016 100644
--- a/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
+++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
@@ -185,15 +185,13 @@ NVC0LegalizePostRA::findFirstUses(
for (Value::UseIterator u = v->uses.begin(); u != v->uses.end(); ++u) {
Instruction *usei = (*u)->getInsn();
- /* XXX HACK ALERT XXX
- *
- * This shouldn't have to be here, we should always be making forward
- * progress by looking at the uses. However this somehow does not
- * appear to be the case. Probably because this is being done right
- * after RA, when the defs/uses lists have been messed with by node
- * merging. This should probably be moved to being done right before
- * RA. But this will do for now.
- */
+ // NOTE: In case of a loop that overwrites a value but never uses
+ // it, it can happen that we have a cycle of uses that consists only
+ // of phis and no-op moves and will thus cause an infinite loop here
+ // since these are not considered actual uses.
+ // The most obvious (and perhaps the only) way to prevent this is to
+ // remember which instructions we've already visited.
+
if (visited.find(usei) != visited.end())
continue;