[Mesa-dev] [PATCH 1/2] ac: fix broken elimination of duplicated VS exports

[Marek Olšák]

From: Marek Olšák <marek.olsak at amd.com>

The renumbering code didn't take into account that multiple VS exports
can have the same PARAM index. This also significantly simplifies
the renumbering. Thankfully, we have piglits for this:

    spec at arb_gpu_shader5@arb_gpu_shader5-interpolateatcentroid-packing
    spec at glsl-1.50@execution at interface-blocks-complex-vs-fs

Reported by Michel Dänzer.
---
 src/amd/common/ac_llvm_build.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/src/amd/common/ac_llvm_build.c b/src/amd/common/ac_llvm_build.c
index 9853d17..87a1fb7 100644
--- a/src/amd/common/ac_llvm_build.c
+++ b/src/amd/common/ac_llvm_build.c
@@ -1401,37 +1401,37 @@ void ac_optimize_vs_outputs(struct ac_llvm_context *ctx,
 				exports.exp[exports.num++] = exp;
 			}
 		}
 		bb = LLVMGetNextBasicBlock(bb);
 	}
 
 	/* Remove holes in export memory due to removed PARAM exports.
 	 * This is done by renumbering all PARAM exports.
 	 */
 	if (removed_any) {
-		uint8_t current_offset[VARYING_SLOT_MAX];
-		unsigned new_count = 0;
+		uint8_t old_offset[VARYING_SLOT_MAX];
 		unsigned out, i;
 
 		/* Make a copy of the offsets. We need the old version while
 		 * we are modifying some of them. */
-		memcpy(current_offset, vs_output_param_offset,
-		       sizeof(current_offset));
+		memcpy(old_offset, vs_output_param_offset,
+		       sizeof(old_offset));
 
 		for (i = 0; i < exports.num; i++) {
 			unsigned offset = exports.exp[i].offset;
 
+			/* Update vs_output_param_offset. Multiple outputs can
+			 * have the same offset.
+			 */
 			for (out = 0; out < num_outputs; out++) {
-				if (current_offset[out] != offset)
-					continue;
-
-				LLVMSetOperand(exports.exp[i].inst, AC_EXP_TARGET,
-					       LLVMConstInt(ctx->i32,
-							    V_008DFC_SQ_EXP_PARAM + new_count, 0));
-				vs_output_param_offset[out] = new_count;
-				new_count++;
-				break;
+				if (old_offset[out] == offset)
+					vs_output_param_offset[out] = i;
 			}
+
+			/* Change the PARAM offset in the instruction. */
+			LLVMSetOperand(exports.exp[i].inst, AC_EXP_TARGET,
+				       LLVMConstInt(ctx->i32,
+						    V_008DFC_SQ_EXP_PARAM + i, 0));
 		}
-		*num_param_exports = new_count;
+		*num_param_exports = exports.num;
 	}
 }
-- 
2.7.4