From: Marek Olšák <marek.ol...@amd.com>
This is for 12.0 and older. A different commit fixes 13.0 and newer.
Cc: 11.2 12.0 <mesa-sta...@lists.freedesktop.org>
---
src/gallium/drivers/radeon/radeon_setup_tgsi_llvm.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)
diff --git a/src/gallium/drivers/radeon/radeon_setup_tgsi_llvm.c
b/src/gallium/drivers/radeon/radeon_setup_tgsi_llvm.c
index 74b36ec..9893bfe 100644
--- a/src/gallium/drivers/radeon/radeon_setup_tgsi_llvm.c
+++ b/src/gallium/drivers/radeon/radeon_setup_tgsi_llvm.c
@@ -1326,23 +1326,32 @@ static void emit_lsb(const struct lp_build_tgsi_action
* action,
struct lp_build_emit_data * emit_data)
{
struct gallivm_state *gallivm = bld_base->base.gallivm;
+ LLVMBuilderRef builder = gallivm->builder;
LLVMValueRef args[2] = {
emit_data->args[0],
/* The value of 1 means that ffs(x=0) = undef, so LLVM won't
* add special code to check for x=0. The reason is that
* the LLVM behavior for x=0 is different from what we
- * need here.
- *
- * The hardware already implements the correct behavior.
+ * need here. However, LLVM also assumes that ffs(x) is
+ * in [0, 31], but GLSL expects that ffs(0) = -1, so
+ * a conditional assignment to handle 0 is still required.
*/
- lp_build_const_int32(gallivm, 1)
+ LLVMConstInt(LLVMInt1TypeInContext(gallivm->context), 1, 0)
};
- emit_data->output[emit_data->chan] =
+ LLVMValueRef lsb =
lp_build_intrinsic(gallivm->builder, "llvm.cttz.i32",
emit_data->dst_type, args, ARRAY_SIZE(args),
LLVMReadNoneAttribute);
+
+ /* TODO: We need an intrinsic to skip this conditional. */
+ /* Check for zero: */
+ emit_data->output[emit_data->chan] =
+ LLVMBuildSelect(builder,
+ LLVMBuildICmp(builder, LLVMIntEQ, args[0],
+ bld_base->uint_bld.zero, ""),
+ lp_build_const_int32(gallivm, -1), lsb, "");
}
/* Find the last bit set. */
--
2.7.4
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