Index: llvm/trunk/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
===================================================================
--- llvm/trunk/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ llvm/trunk/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -4034,11 +4034,13 @@
                                             O0.getNode(), O1.getNode());
     };
 
+    // FIXME: When the semantics of the interaction between select and undef
+    // are clearly defined, it may turn out to be unnecessary to break here.
     SDValue TrueRes = TryFold(ConstTrue);
-    if (!TrueRes)
+    if (!TrueRes || TrueRes.isUndef())
       break;
     SDValue FalseRes = TryFold(ConstFalse);
-    if (!FalseRes)
+    if (!FalseRes || FalseRes.isUndef())
       break;
 
     // For us to materialize these using one instruction, we must be able to
Index: llvm/trunk/test/CodeGen/PowerPC/PR33636.ll
===================================================================
--- llvm/trunk/test/CodeGen/PowerPC/PR33636.ll
+++ llvm/trunk/test/CodeGen/PowerPC/PR33636.ll
@@ -0,0 +1,702 @@
+; Just a test case for a crash reported in
+; https://bugs.llvm.org/show_bug.cgi?id=33636
+; RUN: llc < %s | FileCheck %s
+@g_225 = external unnamed_addr global i16, align 2
+@g_756 = external global [6 x i32], align 4
+@g_3456 = external global i32, align 4
+@g_3708 = external global [9 x i32], align 4
+@g_1252 = external global i8*, align 8
+@g_3043 = external global float*, align 8
+
+; Function Attrs: nounwind
+define void @main() {
+  br i1 undef, label %1, label %4
+
+; <label>:1:                                      ; preds = %0
+  br i1 undef, label %2, label %3
+
+; <label>:2:                                      ; preds = %1
+  br label %3
+
+; <label>:3:                                      ; preds = %2, %1
+  br label %4
+
+; <label>:4:                                      ; preds = %3, %0
+  br label %5
+
+; <label>:5:                                      ; preds = %5, %4
+  br i1 undef, label %6, label %5
+
+; <label>:6:                                      ; preds = %5
+  br i1 undef, label %7, label %8
+
+; <label>:7:                                      ; preds = %6
+  br i1 undef, label %70, label %69
+
+; <label>:8:                                      ; preds = %6
+  br i1 undef, label %9, label %50
+
+; <label>:9:                                      ; preds = %8
+  br label %11
+
+; <label>:10:                                     ; preds = %28
+  br i1 undef, label %11, label %12
+
+; <label>:11:                                     ; preds = %10, %9
+  br label %13
+
+; <label>:12:                                     ; preds = %10
+  br label %30
+
+; <label>:13:                                     ; preds = %23, %11
+  br i1 undef, label %17, label %14
+
+; <label>:14:                                     ; preds = %13
+  br i1 undef, label %16, label %15
+
+; <label>:15:                                     ; preds = %14
+  br label %22
+
+; <label>:16:                                     ; preds = %14
+  br label %17
+
+; <label>:17:                                     ; preds = %16, %13
+  br i1 undef, label %18, label %19
+
+; <label>:18:                                     ; preds = %17
+  br label %19
+
+; <label>:19:                                     ; preds = %18, %17
+  br i1 undef, label %48, label %20
+
+; <label>:20:                                     ; preds = %19
+  br i1 undef, label %48, label %21
+
+; <label>:21:                                     ; preds = %20
+  br label %22
+
+; <label>:22:                                     ; preds = %21, %15
+  br i1 undef, label %23, label %24
+
+; <label>:23:                                     ; preds = %22
+  br label %13
+
+; <label>:24:                                     ; preds = %22
+  br i1 undef, label %28, label %25
+
+; <label>:25:                                     ; preds = %24
+  br label %26
+
+; <label>:26:                                     ; preds = %26, %25
+  br i1 undef, label %26, label %27
+
+; <label>:27:                                     ; preds = %26
+  br label %48
+
+; <label>:28:                                     ; preds = %24
+  br i1 undef, label %29, label %10
+
+; <label>:29:                                     ; preds = %28
+  br label %48
+
+; <label>:30:                                     ; preds = %33, %12
+  br i1 undef, label %32, label %33
+
+; <label>:31:                                     ; preds = %33
+  br label %34
+
+; <label>:32:                                     ; preds = %30
+  br label %33
+
+; <label>:33:                                     ; preds = %32, %30
+  br i1 undef, label %30, label %31
+
+; <label>:34:                                     ; preds = %47, %31
+  br i1 undef, label %35, label %36
+
+; <label>:35:                                     ; preds = %34
+  br label %36
+
+; <label>:36:                                     ; preds = %35, %34
+  br label %37
+
+; <label>:37:                                     ; preds = %45, %36
+  br i1 undef, label %40, label %38
+
+; <label>:38:                                     ; preds = %37
+  br i1 undef, label %39, label %46
+
+; <label>:39:                                     ; preds = %38
+  br label %41
+
+; <label>:40:                                     ; preds = %37
+  br label %41
+
+; <label>:41:                                     ; preds = %40, %39
+  br label %42
+
+; <label>:42:                                     ; preds = %44, %41
+  br i1 undef, label %43, label %44
+
+; <label>:43:                                     ; preds = %42
+  br label %44
+
+; <label>:44:                                     ; preds = %43, %42
+  br i1 undef, label %42, label %45
+
+; <label>:45:                                     ; preds = %44
+  br i1 undef, label %37, label %47
+
+; <label>:46:                                     ; preds = %38
+  br label %48
+
+; <label>:47:                                     ; preds = %45
+  br i1 undef, label %34, label %49
+
+; <label>:48:                                     ; preds = %46, %29, %27, %20, %19
+  br label %65
+
+; <label>:49:                                     ; preds = %47
+  br label %58
+
+; <label>:50:                                     ; preds = %8
+  br i1 undef, label %52, label %51
+
+; <label>:51:                                     ; preds = %50
+  br label %57
+
+; <label>:52:                                     ; preds = %50
+  br label %53
+
+; <label>:53:                                     ; preds = %56, %52
+  br i1 undef, label %54, label %59
+
+; <label>:54:                                     ; preds = %53
+  br i1 undef, label %60, label %59
+
+; <label>:55:                                     ; preds = %64
+  br label %56
+
+; <label>:56:                                     ; preds = %64, %55
+  br i1 undef, label %57, label %53
+
+; <label>:57:                                     ; preds = %56, %51
+  br label %58
+
+; <label>:58:                                     ; preds = %57, %49
+  br label %65
+
+; <label>:59:                                     ; preds = %63, %62, %61, %60, %54, %53
+  br label %65
+
+; <label>:60:                                     ; preds = %54
+  br i1 undef, label %61, label %59
+
+; <label>:61:                                     ; preds = %60
+  br i1 undef, label %62, label %59
+
+; <label>:62:                                     ; preds = %61
+  br i1 undef, label %63, label %59
+
+; <label>:63:                                     ; preds = %62
+  br i1 undef, label %64, label %59
+
+; <label>:64:                                     ; preds = %63
+  br i1 undef, label %55, label %56
+
+; <label>:65:                                     ; preds = %59, %58, %48
+  br i1 undef, label %66, label %67
+
+; <label>:66:                                     ; preds = %65
+  br label %67
+
+; <label>:67:                                     ; preds = %66, %65
+  br i1 undef, label %68, label %92
+
+; <label>:68:                                     ; preds = %67
+  br label %92
+
+; <label>:69:                                     ; preds = %7
+  br label %70
+
+; <label>:70:                                     ; preds = %69, %7
+  br i1 undef, label %72, label %71
+
+; <label>:71:                                     ; preds = %70
+  br label %72
+
+; <label>:72:                                     ; preds = %71, %70
+  br i1 undef, label %73, label %74
+
+; <label>:73:                                     ; preds = %72
+  br label %74
+
+; <label>:74:                                     ; preds = %73, %72
+  br i1 undef, label %85, label %75
+
+; <label>:75:                                     ; preds = %74
+  br i1 undef, label %84, label %76
+
+; <label>:76:                                     ; preds = %75
+  br i1 undef, label %78, label %77
+
+; <label>:77:                                     ; preds = %77, %76
+  br i1 undef, label %84, label %77
+
+; <label>:78:                                     ; preds = %76
+  br label %79
+
+; <label>:79:                                     ; preds = %83, %78
+  br i1 undef, label %83, label %80
+
+; <label>:80:                                     ; preds = %79
+  br i1 undef, label %81, label %82
+
+; <label>:81:                                     ; preds = %80
+  br label %83
+
+; <label>:82:                                     ; preds = %80
+  br label %83
+
+; <label>:83:                                     ; preds = %82, %81, %79
+  br i1 undef, label %90, label %79
+
+; <label>:84:                                     ; preds = %77, %75
+  br label %92
+
+; <label>:85:                                     ; preds = %74
+  br i1 undef, label %86, label %88
+
+; <label>:86:                                     ; preds = %85
+  br i1 undef, label %89, label %87
+
+; <label>:87:                                     ; preds = %86
+  br i1 undef, label %89, label %88
+
+; <label>:88:                                     ; preds = %87, %85
+  br label %89
+
+; <label>:89:                                     ; preds = %88, %87, %86
+  br label %92
+
+; <label>:90:                                     ; preds = %83
+  br i1 undef, label %92, label %91
+
+; <label>:91:                                     ; preds = %90
+  br label %92
+
+; <label>:92:                                     ; preds = %91, %90, %89, %84, %68, %67
+  br label %93
+
+; <label>:93:                                     ; preds = %100, %92
+  br label %94
+
+; <label>:94:                                     ; preds = %98, %93
+  br label %95
+
+; <label>:95:                                     ; preds = %97, %94
+  br i1 undef, label %96, label %97
+
+; <label>:96:                                     ; preds = %95
+  br label %97
+
+; <label>:97:                                     ; preds = %96, %95
+  br i1 undef, label %95, label %98
+
+; <label>:98:                                     ; preds = %97
+  store i32 7, i32* getelementptr inbounds ([9 x i32], [9 x i32]* @g_3708, i64 0, i64 7), align 4
+  %99 = load volatile i32, i32* @g_3456, align 4
+  br i1 undef, label %94, label %100
+
+; <label>:100:                                    ; preds = %98
+  br i1 undef, label %93, label %101
+
+; <label>:101:                                    ; preds = %100
+  br label %102
+
+; <label>:102:                                    ; preds = %117, %101
+  br label %103
+
+; <label>:103:                                    ; preds = %109, %102
+  store i8** @g_1252, i8*** undef, align 8
+  br i1 undef, label %105, label %104
+
+; <label>:104:                                    ; preds = %103
+  br label %105
+
+; <label>:105:                                    ; preds = %104, %103
+  %106 = icmp eq i32 0, 0
+  br i1 %106, label %107, label %116
+
+; <label>:107:                                    ; preds = %105
+  br i1 icmp ne (i32* getelementptr inbounds ([6 x i32], [6 x i32]* @g_756, i64 0, i64 0), i32* getelementptr inbounds ([9 x i32], [9 x i32]* @g_3708, i64 0, i64 4)), label %109, label %108
+
+; <label>:108:                                    ; preds = %107
+  br label %109
+
+; <label>:109:                                    ; preds = %108, %107
+  %110 = phi i32 [ sdiv (i32 32, i32 zext (i1 icmp eq (i32* getelementptr inbounds ([6 x i32], [6 x i32]* @g_756, i64 0, i64 0), i32* getelementptr inbounds ([9 x i32], [9 x i32]* @g_3708, i64 0, i64 4)) to i32)), %108 ], [ 32, %107 ]
+  %111 = trunc i32 %110 to i8
+  %112 = icmp ne i8 %111, 0
+  %113 = and i1 %112, icmp eq (i32* getelementptr inbounds ([6 x i32], [6 x i32]* @g_756, i64 0, i64 0), i32* getelementptr inbounds ([9 x i32], [9 x i32]* @g_3708, i64 0, i64 4))
+  %114 = zext i1 %113 to i16
+  store i16 %114, i16* @g_225, align 2
+  %115 = load volatile float*, float** @g_3043, align 8
+  br i1 undef, label %103, label %117
+
+; <label>:116:                                    ; preds = %105
+  br label %119
+
+; <label>:117:                                    ; preds = %109
+  br i1 undef, label %102, label %118
+
+; <label>:118:                                    ; preds = %117
+  br label %119
+
+; <label>:119:                                    ; preds = %118, %116
+  br i1 undef, label %120, label %231
+
+; <label>:120:                                    ; preds = %119
+  br label %232
+
+; <label>:121:                                    ; preds = %230
+  br label %122
+
+; <label>:122:                                    ; preds = %230, %121
+  br i1 undef, label %124, label %123
+
+; <label>:123:                                    ; preds = %122
+  br label %124
+
+; <label>:124:                                    ; preds = %123, %122
+  br i1 undef, label %228, label %225
+
+; <label>:125:                                    ; preds = %218
+  br label %127
+
+; <label>:126:                                    ; preds = %218
+  br label %127
+
+; <label>:127:                                    ; preds = %216, %126, %125
+  br i1 undef, label %204, label %128
+
+; <label>:128:                                    ; preds = %127
+  br label %205
+
+; <label>:129:                                    ; preds = %216
+  br i1 undef, label %131, label %130
+
+; <label>:130:                                    ; preds = %129
+  br label %131
+
+; <label>:131:                                    ; preds = %130, %129
+  br i1 undef, label %133, label %132
+
+; <label>:132:                                    ; preds = %131
+  br label %133
+
+; <label>:133:                                    ; preds = %132, %131
+  br label %134
+
+; <label>:134:                                    ; preds = %203, %133
+  br i1 undef, label %193, label %135
+
+; <label>:135:                                    ; preds = %134
+  br label %194
+
+; <label>:136:                                    ; preds = %203
+  br i1 undef, label %138, label %137
+
+; <label>:137:                                    ; preds = %136
+  br label %138
+
+; <label>:138:                                    ; preds = %137, %136
+  br i1 undef, label %192, label %139
+
+; <label>:139:                                    ; preds = %138
+  br label %191
+
+; <label>:140:                                    ; preds = %191, %190
+  br i1 undef, label %180, label %141
+
+; <label>:141:                                    ; preds = %140
+  br label %181
+
+; <label>:142:                                    ; preds = %190
+  br i1 undef, label %143, label %178
+
+; <label>:143:                                    ; preds = %142
+  br label %179
+
+; <label>:144:                                    ; preds = %179
+  br label %176
+
+; <label>:145:                                    ; preds = %179
+  br label %176
+
+; <label>:146:                                    ; preds = %177, %175, %174
+  br i1 undef, label %165, label %147
+
+; <label>:147:                                    ; preds = %146
+  br label %166
+
+; <label>:148:                                    ; preds = %174
+  br label %149
+
+; <label>:149:                                    ; preds = %164, %148
+  br i1 undef, label %154, label %150
+
+; <label>:150:                                    ; preds = %149
+  br label %155
+
+; <label>:151:                                    ; preds = %164
+  br i1 undef, label %153, label %152
+
+; <label>:152:                                    ; preds = %151
+  br label %153
+
+; <label>:153:                                    ; preds = %152, %151
+  ret void
+
+; <label>:154:                                    ; preds = %149
+  br label %155
+
+; <label>:155:                                    ; preds = %154, %150
+  br i1 undef, label %157, label %156
+
+; <label>:156:                                    ; preds = %155
+  br label %158
+
+; <label>:157:                                    ; preds = %155
+  br label %158
+
+; <label>:158:                                    ; preds = %157, %156
+  br i1 undef, label %160, label %159
+
+; <label>:159:                                    ; preds = %158
+  br label %161
+
+; <label>:160:                                    ; preds = %158
+  br label %161
+
+; <label>:161:                                    ; preds = %160, %159
+  br i1 undef, label %163, label %162
+
+; <label>:162:                                    ; preds = %161
+  br label %164
+
+; <label>:163:                                    ; preds = %161
+  br label %164
+
+; <label>:164:                                    ; preds = %163, %162
+  br i1 undef, label %151, label %149
+
+; <label>:165:                                    ; preds = %146
+  br label %166
+
+; <label>:166:                                    ; preds = %165, %147
+  br i1 undef, label %168, label %167
+
+; <label>:167:                                    ; preds = %166
+  br label %169
+
+; <label>:168:                                    ; preds = %166
+  br label %169
+
+; <label>:169:                                    ; preds = %168, %167
+  br i1 undef, label %171, label %170
+
+; <label>:170:                                    ; preds = %169
+  br label %172
+
+; <label>:171:                                    ; preds = %169
+  br label %172
+
+; <label>:172:                                    ; preds = %171, %170
+  br i1 undef, label %174, label %173
+
+; <label>:173:                                    ; preds = %172
+  br label %174
+
+; <label>:174:                                    ; preds = %173, %172
+  br i1 undef, label %148, label %146
+
+; <label>:175:                                    ; preds = %176
+  br label %146
+
+; <label>:176:                                    ; preds = %145, %144
+  br i1 undef, label %177, label %175
+
+; <label>:177:                                    ; preds = %176
+  br label %146
+
+; <label>:178:                                    ; preds = %142
+  br label %179
+
+; <label>:179:                                    ; preds = %178, %143
+  br i1 undef, label %145, label %144
+
+; <label>:180:                                    ; preds = %140
+  br label %181
+
+; <label>:181:                                    ; preds = %180, %141
+  br i1 undef, label %183, label %182
+
+; <label>:182:                                    ; preds = %181
+  br label %184
+
+; <label>:183:                                    ; preds = %181
+  br label %184
+
+; <label>:184:                                    ; preds = %183, %182
+  br i1 undef, label %186, label %185
+
+; <label>:185:                                    ; preds = %184
+  br label %187
+
+; <label>:186:                                    ; preds = %184
+  br label %187
+
+; <label>:187:                                    ; preds = %186, %185
+  br i1 undef, label %189, label %188
+
+; <label>:188:                                    ; preds = %187
+  br label %190
+
+; <label>:189:                                    ; preds = %187
+  br label %190
+
+; <label>:190:                                    ; preds = %189, %188
+  br i1 undef, label %142, label %140
+
+; <label>:191:                                    ; preds = %192, %139
+  br label %140
+
+; <label>:192:                                    ; preds = %138
+  br label %191
+
+; <label>:193:                                    ; preds = %134
+  br label %194
+
+; <label>:194:                                    ; preds = %193, %135
+  br i1 undef, label %196, label %195
+
+; <label>:195:                                    ; preds = %194
+  br label %197
+
+; <label>:196:                                    ; preds = %194
+  br label %197
+
+; <label>:197:                                    ; preds = %196, %195
+  br i1 undef, label %199, label %198
+
+; <label>:198:                                    ; preds = %197
+  br label %200
+
+; <label>:199:                                    ; preds = %197
+  br label %200
+
+; <label>:200:                                    ; preds = %199, %198
+  br i1 undef, label %202, label %201
+
+; <label>:201:                                    ; preds = %200
+  br label %203
+
+; <label>:202:                                    ; preds = %200
+  br label %203
+
+; <label>:203:                                    ; preds = %202, %201
+  br i1 undef, label %136, label %134
+
+; <label>:204:                                    ; preds = %127
+  br label %205
+
+; <label>:205:                                    ; preds = %204, %128
+  br i1 undef, label %207, label %206
+
+; <label>:206:                                    ; preds = %205
+  br label %208
+
+; <label>:207:                                    ; preds = %205
+  br label %208
+
+; <label>:208:                                    ; preds = %207, %206
+  br i1 undef, label %210, label %209
+
+; <label>:209:                                    ; preds = %208
+  br label %211
+
+; <label>:210:                                    ; preds = %208
+  br label %211
+
+; <label>:211:                                    ; preds = %210, %209
+  br i1 undef, label %213, label %212
+
+; <label>:212:                                    ; preds = %211
+  br label %214
+
+; <label>:213:                                    ; preds = %211
+  br label %214
+
+; <label>:214:                                    ; preds = %213, %212
+  br i1 undef, label %216, label %215
+
+; <label>:215:                                    ; preds = %214
+  br label %216
+
+; <label>:216:                                    ; preds = %215, %214
+  br i1 undef, label %129, label %127
+
+; <label>:217:                                    ; preds = %220
+  br label %218
+
+; <label>:218:                                    ; preds = %221, %217
+  br i1 undef, label %126, label %125
+
+; <label>:219:                                    ; preds = %223
+  br label %220
+
+; <label>:220:                                    ; preds = %224, %219
+  br i1 undef, label %221, label %217
+
+; <label>:221:                                    ; preds = %220
+  br label %218
+
+; <label>:222:                                    ; preds = %226
+  br label %223
+
+; <label>:223:                                    ; preds = %227, %222
+  br i1 undef, label %224, label %219
+
+; <label>:224:                                    ; preds = %223
+  br label %220
+
+; <label>:225:                                    ; preds = %124
+  br label %226
+
+; <label>:226:                                    ; preds = %228, %225
+  br i1 undef, label %227, label %222
+
+; <label>:227:                                    ; preds = %226
+  br label %223
+
+; <label>:228:                                    ; preds = %124
+  br label %226
+
+; <label>:229:                                    ; preds = %232
+  br label %230
+
+; <label>:230:                                    ; preds = %233, %229
+  br i1 undef, label %122, label %121
+
+; <label>:231:                                    ; preds = %119
+  br label %232
+
+; <label>:232:                                    ; preds = %231, %120
+  br i1 undef, label %233, label %229
+
+; <label>:233:                                    ; preds = %232
+  br label %230
+
+; CHECK: blr
+}