Mesa (master): gallivm,tgsi: fix idiv by zero crash

[Roland Scheidegger]

Module: Mesa
Branch: master
Commit: ffeb77c7b0552a8624e46e65d6347240ac5ae84d
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=ffeb77c7b0552a8624e46e65d6347240ac5ae84d

Author: rconde <rconde01 at outlook.com>
Date:   Wed Sep 17 18:30:23 2014 +0200

gallivm,tgsi: fix idiv by zero crash

While the result of signed integer division by zero is undefined by glsl
(and doesn't exist with d3d10), we must not crash, so need to make sure we
don't get sigfpe much like udiv already does.
Unlike udiv where we return 0xffffffff (as required by d3d10) there is
no requirement right now to return anything specific so we use zero.

---

 src/gallium/auxiliary/gallivm/lp_bld_tgsi_action.c |   24 +++++++++++++++++---
 src/gallium/auxiliary/tgsi/tgsi_exec.c             |    8 +++----
 2 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_tgsi_action.c b/src/gallium/auxiliary/gallivm/lp_bld_tgsi_action.c
index b9546db..4a9bc1f 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_tgsi_action.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_tgsi_action.c
@@ -1248,8 +1248,26 @@ idiv_emit_cpu(
    struct lp_build_tgsi_context * bld_base,
    struct lp_build_emit_data * emit_data)
 {
-   emit_data->output[emit_data->chan] = lp_build_div(&bld_base->int_bld,
-                                   emit_data->args[0], emit_data->args[1]);
+   LLVMBuilderRef builder = bld_base->base.gallivm->builder;
+   LLVMValueRef div_mask = lp_build_cmp(&bld_base->uint_bld,
+                                        PIPE_FUNC_EQUAL, emit_data->args[1],
+                                        bld_base->uint_bld.zero);
+   /* We want to make sure that we never divide/mod by zero to not 
+    * generate sigfpe. We don't want to crash just because the 
+    * shader is doing something weird. */
+   LLVMValueRef divisor = LLVMBuildOr(builder,
+                                      div_mask,
+                                      emit_data->args[1], "");
+   LLVMValueRef result = lp_build_div(&bld_base->uint_bld,
+                                      emit_data->args[0], divisor);
+                                      
+   LLVMValueRef not_div_mask = LLVMBuildNot(builder,
+                                            div_mask,"");
+                                          
+   /* idiv by zero doesn't have a guaranteed return value chose 0 for now. */
+   emit_data->output[emit_data->chan] = LLVMBuildAnd(builder,
+                                                     not_div_mask,
+                                                     result, "");
 }
 
 /* TGSI_OPCODE_INEG (CPU Only) */
@@ -1683,7 +1701,7 @@ udiv_emit_cpu(
                                       emit_data->args[1], "");
    LLVMValueRef result = lp_build_div(&bld_base->uint_bld,
                                       emit_data->args[0], divisor);
-   /* udiv by zero is guaranteed to return 0xffffffff */
+   /* udiv by zero is guaranteed to return 0xffffffff at least with d3d10 */
    emit_data->output[emit_data->chan] = LLVMBuildOr(builder,
                                                     div_mask,
                                                     result, "");
diff --git a/src/gallium/auxiliary/tgsi/tgsi_exec.c b/src/gallium/auxiliary/tgsi/tgsi_exec.c
index 6dae379..7794801 100644
--- a/src/gallium/auxiliary/tgsi/tgsi_exec.c
+++ b/src/gallium/auxiliary/tgsi/tgsi_exec.c
@@ -3343,10 +3343,10 @@ micro_idiv(union tgsi_exec_channel *dst,
            const union tgsi_exec_channel *src0,
            const union tgsi_exec_channel *src1)
 {
-   dst->i[0] = src0->i[0] / src1->i[0];
-   dst->i[1] = src0->i[1] / src1->i[1];
-   dst->i[2] = src0->i[2] / src1->i[2];
-   dst->i[3] = src0->i[3] / src1->i[3];
+   dst->i[0] = src1->i[0] ? src0->i[0] / src1->i[0] : 0;
+   dst->i[1] = src1->i[1] ? src0->i[1] / src1->i[1] : 0;
+   dst->i[2] = src1->i[2] ? src0->i[2] / src1->i[2] : 0;
+   dst->i[3] = src1->i[3] ? src0->i[3] / src1->i[3] : 0;
 }
 
 static void