Make branch hint warnings optional, defaulting to off.

Signed-off-by: Chris Dodd <[email protected]>

Author: ChrisDodd

frontends/common/constantFolding.cpp

@@ -1122,7 +1122,8 @@ class FilterLikelyAnnot : public Transform {
         prune();
         if (annot->name == IR::Annotation::likelyAnnotation) return nullptr;
         if (annot->name == IR::Annotation::unlikelyAnnotation) {
-            warning(ErrorType::WARN_IGNORE, "ignoring %1% on always taken statement", annot);
+            // FIXME -- disable this warning due to worries it will trigger too often
+            warning(ErrorType::WARN_BRANCH_HINT, "ignoring %1% on always taken statement", annot);
             return nullptr;
         }
         return annot;
@@ -1134,13 +1135,15 @@ const IR::Node *DoConstantFolding::postorder(IR::IfStatement *ifstmt) {
         if (cond->value) {
             if (auto blk = ifstmt->ifFalse ? ifstmt->ifFalse->to<IR::BlockStatement>() : nullptr) {
                 if (auto annot = blk->getAnnotation(IR::Annotation::likelyAnnotation))
-                    warning(ErrorType::WARN_IGNORE, "ignoring %1% on never taken statement", annot);
+                    warning(ErrorType::WARN_BRANCH_HINT, "ignoring %1% on never taken statement",
+                            annot);
             }
             return ifstmt->ifTrue->apply(FilterLikelyAnnot());
         } else {
             if (auto blk = ifstmt->ifTrue->to<IR::BlockStatement>()) {
                 if (auto annot = blk->getAnnotation(IR::Annotation::likelyAnnotation))
-                    warning(ErrorType::WARN_IGNORE, "ignoring %1% on never taken statement", annot);
+                    warning(ErrorType::WARN_BRANCH_HINT, "ignoring %1% on never taken statement",
+                            annot);
             }
             if (ifstmt->ifFalse == nullptr) {
                 return new IR::EmptyStatement(ifstmt->srcInfo);

lib/error_catalog.cpp

@@ -18,6 +18,7 @@ limitations under the License.
 
 #include <map>
 
+#include "error_reporter.h"
 #include "lib/cstring.h"
 
 namespace P4 {
@@ -71,6 +72,7 @@ const int ErrorType::WARN_ENTRIES_OUT_OF_ORDER = 1022;
 const int ErrorType::WARN_MULTI_HDR_EXTRACT = 1023;
 const int ErrorType::WARN_EXPRESSION = 1024;
 const int ErrorType::WARN_DUPLICATE = 1025;
+const int ErrorType::WARN_BRANCH_HINT = 1026;
 
 // ------ Info messages -----------
 const int ErrorType::INFO_INFERRED = WARN_MAX + 1;
@@ -124,9 +126,16 @@ std::map<int, cstring> ErrorCatalog::errorCatalog = {
     {ErrorType::WARN_MULTI_HDR_EXTRACT, "multi_header_extract"_cs},
     {ErrorType::WARN_EXPRESSION, "expr"_cs},
     {ErrorType::WARN_DUPLICATE, "duplicate"_cs},
+    {ErrorType::WARN_BRANCH_HINT, "branch"_cs},
 
     // Info messages
     {ErrorType::INFO_INFERRED, "inferred"_cs},
     {ErrorType::INFO_PROGRESS, "progress"_cs}};
 
+void ErrorCatalog::initReporter(ErrorReporter &reporter) {
+    // by default, ignore warnings about branch hints -- user can turn them
+    // on with --Wwarn=branch
+    reporter.setDiagnosticAction("branch"_cs, DiagnosticAction::Ignore);
+}
+
 }  // namespace P4

lib/error_catalog.h

@@ -28,6 +28,8 @@ namespace P4 {
 
 using MessageType = ErrorMessage::MessageType;
 
+class ErrorReporter;
+
 /// enumerate supported errors
 /// It is a class and not an enum class because in C++11 you can't extend an enum class
 class ErrorType {
@@ -85,6 +87,7 @@ class ErrorType {
     static const int WARN_MULTI_HDR_EXTRACT;        // same header may be extracted more than once
     static const int WARN_EXPRESSION;               // expression related warnings
     static const int WARN_DUPLICATE;                // duplicate objects
+    static const int WARN_BRANCH_HINT;              // branch frequency/likely hints
     // Backends should extend this class with additional warnings in the range 1500-2141.
     static const int WARN_MIN_BACKEND = 1500;  // first allowed backend warning code
     static const int WARN_MAX = 2141;          // last allowed warning code
@@ -155,6 +158,8 @@ class ErrorCatalog {
         return error;
     }
 
+    void initReporter(ErrorReporter &reporter);
+
  private:
     ErrorCatalog() {}
 

lib/error_reporter.h

@@ -91,6 +91,7 @@ class ErrorReporter {
           defaultInfoDiagnosticAction(DiagnosticAction::Info),
           defaultWarningDiagnosticAction(DiagnosticAction::Warn) {
         outputstream = &std::cerr;
+        ErrorCatalog::getCatalog().initReporter(*this);
     }
     virtual ~ErrorReporter() = default;
 

testdata/p4_16_samples/annotation-likely.p4

@@ -1,5 +1,7 @@
 #include <core.p4>
 
+@command_line("--Wwarn=branch")
+
 struct Headers {
     bit<8> a;
     bit<8> b;

testdata/p4_16_samples_outputs/annotation-likely-first.p4

@@ -1,6 +1,6 @@
 #include <core.p4>
 
-struct Headers {
+@command_line("--Wwarn=branch") struct Headers {
     bit<8> a;
     bit<8> b;
 }

testdata/p4_16_samples_outputs/annotation-likely-frontend.p4

@@ -1,6 +1,6 @@
 #include <core.p4>
 
-struct Headers {
+@command_line("--Wwarn=branch") struct Headers {
     bit<8> a;
     bit<8> b;
 }

testdata/p4_16_samples_outputs/annotation-likely-midend.p4

@@ -1,23 +1,23 @@
 #include <core.p4>
 
-struct Headers {
+@command_line("--Wwarn=branch") struct Headers {
     bit<8> a;
     bit<8> b;
 }
 
 control ingress(inout Headers h) {
-    @hidden action annotationlikely11() {
+    @hidden action annotationlikely13() {
         h.a = 8w0;
         h.b = 8w0;
     }
-    @hidden table tbl_annotationlikely11 {
+    @hidden table tbl_annotationlikely13 {
         actions = {
-            annotationlikely11();
+            annotationlikely13();
         }
-        const default_action = annotationlikely11();
+        const default_action = annotationlikely13();
     }
     apply {
-        tbl_annotationlikely11.apply();
+        tbl_annotationlikely13.apply();
     }
 }
 

testdata/p4_16_samples_outputs/annotation-likely.p4

@@ -1,6 +1,6 @@
 #include <core.p4>
 
-struct Headers {
+@command_line("--Wwarn=branch") struct Headers {
     bit<8> a;
     bit<8> b;
 }

testdata/p4_16_samples_outputs/annotation-likely.p4-stderr

@@ -1,6 +1,6 @@
-annotation-likely.p4(13): [--Wwarn=ignore] warning: ignoring @unlikely on always taken statement
+annotation-likely.p4(15): [--Wwarn=branch] warning: ignoring @unlikely on always taken statement
         if (true) @unlikely {
                   ^
-annotation-likely.p4(16): [--Wwarn=ignore] warning: ignoring @likely on never taken statement
+annotation-likely.p4(18): [--Wwarn=branch] warning: ignoring @likely on never taken statement
         if (h.a != h.a) @likely {
                         ^