Fix for issue #513: better error message

midend/predication.h

@@ -20,11 +20,16 @@ limitations under the License.
 #include "ir/ir.h"
 #include "frontends/p4/typeChecking/typeChecker.h"
 
-// Converts if statements to ?: in actions, if possible
-// For this to work all statements must be assignments or other ifs.
 namespace P4 {
 
-/*
+/**
+
+This pass operates on action bodies.  It converts 'if' statements to
+'?:' expressions, if possible.  Otherwise this pass will signal an
+error.  This pass should be used only on architectures that do not
+support conditionals in actions.
+
+For this to work all statements must be assignments or other ifs.
 
 if (e)
    a = f(b);
@@ -65,7 +70,8 @@ class Predication final : public Transform {
         return new IR::PathExpression(IR::ID(predicateName.back())); }
     const IR::Statement* error(const IR::Statement* statement) const {
         if (inside_action && ifNestingLevel > 0)
-            ::error("%1%: Predication cannot be applied", statement);
+            ::error("%1%: Conditional execution in actions is not supported on this target",
+                    statement);
         return statement;
     }
 

testdata/p4_16_errors/issue513.p4

@@ -0,0 +1,95 @@
+/*
+Copyright 2017 Cisco Systems, Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+#include <core.p4>
+#include <v1model.p4>
+
+typedef bit<48>  EthernetAddress;
+
+header Ethernet_h {
+    EthernetAddress dstAddr;
+    EthernetAddress srcAddr;
+    bit<16>         etherType;
+}
+
+struct Parsed_packet {
+    Ethernet_h    ethernet;
+}
+
+struct mystruct1 {
+    bit<4>  a;
+    bit<4>  b;
+}
+
+control DeparserI(packet_out packet,
+                  in Parsed_packet hdr) {
+    apply { packet.emit(hdr.ethernet); }
+}
+
+parser parserI(packet_in pkt,
+               out Parsed_packet hdr,
+               inout mystruct1 meta,
+               inout standard_metadata_t stdmeta) {
+    state start {
+        pkt.extract(hdr.ethernet);
+        transition accept;
+    }
+}
+
+control cIngress(inout Parsed_packet hdr,
+                 inout mystruct1 meta,
+                 inout standard_metadata_t stdmeta) {
+    action foo() {
+        meta.b = meta.b + 5;
+        if (meta.b > 10) {
+            // Next line causes error for p4test: MethodCallStatement:
+            // Predication cannot be applied.
+            mark_to_drop();
+        }
+    }
+    table guh {
+        key = { hdr.ethernet.srcAddr : exact; }
+        actions = { foo; }
+        default_action = foo;
+    }
+
+    apply {
+        guh.apply();
+    }
+}
+
+control cEgress(inout Parsed_packet hdr,
+                inout mystruct1 meta,
+                inout standard_metadata_t stdmeta) {
+    apply { }
+}
+
+control vc(in Parsed_packet hdr,
+           inout mystruct1 meta) {
+    apply { }
+}
+
+control uc(inout Parsed_packet hdr,
+           inout mystruct1 meta) {
+    apply { }
+}
+
+V1Switch<Parsed_packet, mystruct1>(parserI(),
+                                   vc(),
+                                   cIngress(),
+                                   cEgress(),
+                                   uc(),
+                                   DeparserI()) main;

testdata/p4_16_errors_outputs/issue513-frontend.p4

@@ -0,0 +1,68 @@
+#include <core.p4>
+#include <v1model.p4>
+
+typedef bit<48> EthernetAddress;
+header Ethernet_h {
+    EthernetAddress dstAddr;
+    EthernetAddress srcAddr;
+    bit<16>         etherType;
+}
+
+struct Parsed_packet {
+    Ethernet_h ethernet;
+}
+
+struct mystruct1 {
+    bit<4> a;
+    bit<4> b;
+}
+
+control DeparserI(packet_out packet, in Parsed_packet hdr) {
+    apply {
+        packet.emit<Ethernet_h>(hdr.ethernet);
+    }
+}
+
+parser parserI(packet_in pkt, out Parsed_packet hdr, inout mystruct1 meta, inout standard_metadata_t stdmeta) {
+    state start {
+        pkt.extract<Ethernet_h>(hdr.ethernet);
+        transition accept;
+    }
+}
+
+control cIngress(inout Parsed_packet hdr, inout mystruct1 meta, inout standard_metadata_t stdmeta) {
+    @name("foo") action foo_0() {
+        meta.b = meta.b + 4w5;
+        if (meta.b > 4w10) 
+            mark_to_drop();
+    }
+    @name("guh") table guh_0 {
+        key = {
+            hdr.ethernet.srcAddr: exact @name("hdr.ethernet.srcAddr") ;
+        }
+        actions = {
+            foo_0();
+        }
+        default_action = foo_0();
+    }
+    apply {
+        guh_0.apply();
+    }
+}
+
+control cEgress(inout Parsed_packet hdr, inout mystruct1 meta, inout standard_metadata_t stdmeta) {
+    apply {
+    }
+}
+
+control vc(in Parsed_packet hdr, inout mystruct1 meta) {
+    apply {
+    }
+}
+
+control uc(inout Parsed_packet hdr, inout mystruct1 meta) {
+    apply {
+    }
+}
+
+V1Switch<Parsed_packet, mystruct1>(parserI(), vc(), cIngress(), cEgress(), uc(), DeparserI()) main;

testdata/p4_16_errors_outputs/issue513.p4

@@ -0,0 +1,69 @@
+#include <core.p4>
+#include <v1model.p4>
+
+typedef bit<48> EthernetAddress;
+header Ethernet_h {
+    EthernetAddress dstAddr;
+    EthernetAddress srcAddr;
+    bit<16>         etherType;
+}
+
+struct Parsed_packet {
+    Ethernet_h ethernet;
+}
+
+struct mystruct1 {
+    bit<4> a;
+    bit<4> b;
+}
+
+control DeparserI(packet_out packet, in Parsed_packet hdr) {
+    apply {
+        packet.emit(hdr.ethernet);
+    }
+}
+
+parser parserI(packet_in pkt, out Parsed_packet hdr, inout mystruct1 meta, inout standard_metadata_t stdmeta) {
+    state start {
+        pkt.extract(hdr.ethernet);
+        transition accept;
+    }
+}
+
+control cIngress(inout Parsed_packet hdr, inout mystruct1 meta, inout standard_metadata_t stdmeta) {
+    action foo() {
+        meta.b = meta.b + 5;
+        if (meta.b > 10) {
+            mark_to_drop();
+        }
+    }
+    table guh {
+        key = {
+            hdr.ethernet.srcAddr: exact;
+        }
+        actions = {
+            foo;
+        }
+        default_action = foo;
+    }
+    apply {
+        guh.apply();
+    }
+}
+
+control cEgress(inout Parsed_packet hdr, inout mystruct1 meta, inout standard_metadata_t stdmeta) {
+    apply {
+    }
+}
+
+control vc(in Parsed_packet hdr, inout mystruct1 meta) {
+    apply {
+    }
+}
+
+control uc(inout Parsed_packet hdr, inout mystruct1 meta) {
+    apply {
+    }
+}
+
+V1Switch<Parsed_packet, mystruct1>(parserI(), vc(), cIngress(), cEgress(), uc(), DeparserI()) main;

testdata/p4_16_errors_outputs/issue513.p4-stderr

@@ -0,0 +1,3 @@
+../testdata/p4_16_errors/issue513.p4(60): error: MethodCallStatement: Conditional execution in actions is not supported on this target
+            mark_to_drop();
+            ^^^^^^^^^^^^^^