From 6d731c5651ea98551e0bf0c1a8896d5ea63558d5 Mon Sep 17 00:00:00 2001 From: Connor Abbott Date: Mon, 31 Jul 2017 18:28:45 -0700 Subject: [PATCH] ac/nir: fix lsb emission This makes it match radeonsi. The LLVM backend itself will emit the correct instruction, but LLVM might do incorrect optimizations since it thinks the output is undefined when the input is 0, even though it's not supposed to be. We really need a new intrinsic, or for the backend to become smarter and recognize this pattern. Cc: mesa-stable@lists.freedesktop.org Reviewed-by: Bas Nieuwenhuizen --- src/amd/common/ac_nir_to_llvm.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/src/amd/common/ac_nir_to_llvm.c b/src/amd/common/ac_nir_to_llvm.c index 530b5817af3..19b1ef07155 100644 --- a/src/amd/common/ac_nir_to_llvm.c +++ b/src/amd/common/ac_nir_to_llvm.c @@ -1187,7 +1187,17 @@ static LLVMValueRef emit_find_lsb(struct ac_llvm_context *ctx, */ LLVMConstInt(ctx->i1, 1, false), }; - return ac_build_intrinsic(ctx, "llvm.cttz.i32", ctx->i32, params, 2, AC_FUNC_ATTR_READNONE); + + LLVMValueRef lsb = ac_build_intrinsic(ctx, "llvm.cttz.i32", ctx->i32, + params, 2, + AC_FUNC_ATTR_READNONE); + + /* TODO: We need an intrinsic to skip this conditional. */ + /* Check for zero: */ + return LLVMBuildSelect(ctx->builder, LLVMBuildICmp(ctx->builder, + LLVMIntEQ, src0, + ctx->i32_0, ""), + LLVMConstInt(ctx->i32, -1, 0), lsb, ""); } static LLVMValueRef emit_ifind_msb(struct ac_llvm_context *ctx, -- 2.30.2