Mesa (master): radeonsi: add a workaround for bitfield_extract when count is 0

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Module: Mesa
Branch: master
Commit: 0e6cdfd561c63d23e8ff32df4cab2370dc2a53d2
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=0e6cdfd561c63d23e8ff32df4cab2370dc2a53d2

Author: Timothy Arceri <tarceri at itsqueeze.com>
Date:   Sat Sep 22 12:38:11 2018 +1000

radeonsi: add a workaround for bitfield_extract when count is 0

This ports the fix from 3d41757788ac. Both LLVM 7 & 8 continue
to have this problem.

It fixes rendering issues in some menu and loading screens of
Civ VI which can be seen in the trace from bug 104602.

Note: This does not fix the black triangles on Vega for bug
104602.

Reviewed-by: Marek Olšák <marek.olsak at amd.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104602
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107276

---

 src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c | 41 +++++++++++++++++------
 1 file changed, 30 insertions(+), 11 deletions(-)

diff --git a/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c b/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c
index a768b44904..fca2527f28 100644
--- a/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c
+++ b/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c
@@ -495,18 +495,37 @@ static void emit_bfe(const struct lp_build_tgsi_action *action,
 		     struct lp_build_emit_data *emit_data)
 {
 	struct si_shader_context *ctx = si_shader_context(bld_base);
-	LLVMValueRef bfe_sm5;
-	LLVMValueRef cond;
-
-	bfe_sm5 = ac_build_bfe(&ctx->ac, emit_data->args[0],
-			       emit_data->args[1], emit_data->args[2],
-			       emit_data->info->opcode == TGSI_OPCODE_IBFE);
 
-	/* Correct for GLSL semantics. */
-	cond = LLVMBuildICmp(ctx->ac.builder, LLVMIntUGE, emit_data->args[2],
-			     LLVMConstInt(ctx->i32, 32, 0), "");
-	emit_data->output[emit_data->chan] =
-		LLVMBuildSelect(ctx->ac.builder, cond, emit_data->args[0], bfe_sm5, "");
+	if (HAVE_LLVM < 0x0700) {
+		LLVMValueRef bfe_sm5 =
+			ac_build_bfe(&ctx->ac, emit_data->args[0],
+				     emit_data->args[1], emit_data->args[2],
+				     emit_data->info->opcode == TGSI_OPCODE_IBFE);
+
+		/* Correct for GLSL semantics. */
+		LLVMValueRef cond = LLVMBuildICmp(ctx->ac.builder, LLVMIntUGE, emit_data->args[2],
+						  LLVMConstInt(ctx->i32, 32, 0), "");
+		emit_data->output[emit_data->chan] =
+			LLVMBuildSelect(ctx->ac.builder, cond, emit_data->args[0], bfe_sm5, "");
+	} else {
+		/* FIXME: LLVM 7 returns incorrect result when count is 0.
+		 * https://bugs.freedesktop.org/show_bug.cgi?id=107276
+		 */
+		LLVMValueRef zero = ctx->i32_0;
+		LLVMValueRef bfe_sm5 =
+			ac_build_bfe(&ctx->ac, emit_data->args[0],
+				     emit_data->args[1], emit_data->args[2],
+				     emit_data->info->opcode == TGSI_OPCODE_IBFE);
+
+		/* Correct for GLSL semantics. */
+		LLVMValueRef cond = LLVMBuildICmp(ctx->ac.builder, LLVMIntUGE, emit_data->args[2],
+						  LLVMConstInt(ctx->i32, 32, 0), "");
+		LLVMValueRef cond2 = LLVMBuildICmp(ctx->ac.builder, LLVMIntEQ, emit_data->args[2],
+						   zero, "");
+		bfe_sm5 = LLVMBuildSelect(ctx->ac.builder, cond, emit_data->args[0], bfe_sm5, "");
+		emit_data->output[emit_data->chan] =
+			LLVMBuildSelect(ctx->ac.builder, cond2, zero, bfe_sm5, "");
+	}
 }
 
 /* this is ffs in C */