From ca9ab05d45ebf407485af2daa3742b897ff99162 Mon Sep 17 00:00:00 2001 From: Christoph Bumiller Date: Sat, 6 Sep 2014 01:36:48 +0200 Subject: [PATCH] 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" Reviewed-by: Ilia Mirkin --- .../nouveau/codegen/nv50_ir_lowering_nvc0.cpp | 16 +++++++--------- 1 file 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; -- 2.30.2