Mesa (7.10): glsl: Reinstate constant-folding for division by zero

[Ian Romanick]

Module: Mesa
Branch: 7.10
Commit: 614eff1fc6046f728d9faced84ffedb15cb601b1
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=614eff1fc6046f728d9faced84ffedb15cb601b1

Author: Chad Versace <chad.versace at intel.com>
Date:   Mon Feb 14 13:22:39 2011 -0800

glsl: Reinstate constant-folding for division by zero

Fixes regression: https://bugs.freedesktop.org/show_bug.cgi?id=34160

Commit e7c1f058d18f62aa4871aec623f994d7b68cb8c1 disabled constant-folding
when division-by-zero occured. This was a mistake, because the spec does
allow division by zero. (From section 5.9 of the GLSL 1.20 spec: Dividing
by zero does not cause an exception but does result in an unspecified
value.)

For floating-point division, the original pre-e7c1f05 behavior is
reinstated.

For integer division, constant-fold 1/0 to 0.

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>

(cherry picked from commit 62c8c773334c1b0cdd484997a4ccec8945713f8c)

---

 src/glsl/ir_constant_expression.cpp |   24 ++++++++++++++++++++----
 1 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/src/glsl/ir_constant_expression.cpp b/src/glsl/ir_constant_expression.cpp
index cf958aa..b5850be 100644
--- a/src/glsl/ir_constant_expression.cpp
+++ b/src/glsl/ir_constant_expression.cpp
@@ -514,10 +514,18 @@ ir_expression::constant_expression_value()
 
 	 switch (op[0]->type->base_type) {
 	 case GLSL_TYPE_UINT:
-	    data.u[c] = op[0]->value.u[c0] / op[1]->value.u[c1];
+	    if (op[1]->value.u[c1] == 0) {
+	       data.u[c] = 0;
+	    } else {
+	       data.u[c] = op[0]->value.u[c0] / op[1]->value.u[c1];
+	    }
 	    break;
 	 case GLSL_TYPE_INT:
-	    data.i[c] = op[0]->value.i[c0] / op[1]->value.i[c1];
+	    if (op[1]->value.i[c1] == 0) {
+	       data.i[c] = 0;
+	    } else {
+	       data.i[c] = op[0]->value.i[c0] / op[1]->value.i[c1];
+	    }
 	    break;
 	 case GLSL_TYPE_FLOAT:
 	    data.f[c] = op[0]->value.f[c0] / op[1]->value.f[c1];
@@ -536,10 +544,18 @@ ir_expression::constant_expression_value()
 
 	 switch (op[0]->type->base_type) {
 	 case GLSL_TYPE_UINT:
-	    data.u[c] = op[0]->value.u[c0] % op[1]->value.u[c1];
+	    if (op[1]->value.u[c1] == 0) {
+	       data.u[c] = 0;
+	    } else {
+	       data.u[c] = op[0]->value.u[c0] % op[1]->value.u[c1];
+	    }
 	    break;
 	 case GLSL_TYPE_INT:
-	    data.i[c] = op[0]->value.i[c0] % op[1]->value.i[c1];
+	    if (op[1]->value.i[c1] == 0) {
+	       data.i[c] = 0;
+	    } else {
+	       data.i[c] = op[0]->value.i[c0] % op[1]->value.i[c1];
+	    }
 	    break;
 	 case GLSL_TYPE_FLOAT:
 	    /* We don't use fmod because it rounds toward zero; GLSL specifies