Add braces to some if-stmts in generated Bluesim C++

to avoid warnings about ambiguous 'else'

src/comp/CCSyntax.hs

@@ -675,10 +675,24 @@ instance PPrint CCFragment where
   pPrint d p (CPPInclude file True)  = text ("#include <" ++ file ++ ">")
   pPrint d p (CPPInclude file False) = text ("#include \"" ++ file ++ "\"")
   pPrint d p (CIf c th Nothing)      =
-    (text "if (") <> (pp c) <> (text ")") $+$ (printClauseOrBlock th)
+    -- If the true-arm is a nested if-stmt with an else-clause,
+    -- possibly under layers of for-stmts with single elements,
+    -- then braces are needed to avoid an ambiguous-else warning
+    let needsBraces (CIf _ _ (Just _)) = True
+        needsBraces (CFor _ _ _ b) = needsBraces b
+        needsBraces _ = False
+        th' = if (needsBraces th) then CBlock [th] else th
+    in  (text "if (") <> (pp c) <> (text ")") $+$ (printClauseOrBlock th')
   pPrint d p (CIf c th (Just el))    =
-    (text "if (") <> (pp c) <> (text ")") $+$
-    (printClauseOrBlock th) $+$ (text "else") $+$ (printClauseOrBlock el)
+    -- If the true-arm is a nested if-stmt without an else-clause,
+    -- possibly under layers of for-stmts with single elements,
+    -- then braces are needed for correct parsing
+    let needsBraces (CIf _ _ Nothing) = True
+        needsBraces (CFor _ _ _ b) = needsBraces b
+        needsBraces _ = False
+        th' = if (needsBraces th) then CBlock [th] else th
+    in  (text "if (") <> (pp c) <> (text ")") $+$
+        (printClauseOrBlock th') $+$ (text "else") $+$ (printClauseOrBlock el)
   pPrint d p (CSwitch idx arms deflt) =
     let ppArm (n, blk) = (text "case") <+> (pp n) <> (text ":") $+$
                          nest 2 (vsep (map printStmt blk))

testsuite/bsc.bluesim/misc/NestedIfBraces.bsv

@@ -0,0 +1,28 @@
+
+
+ActionValue #(Bit #(32)) cur_cycle = actionvalue
+                                        Bit #(32) t <- $stime;
+                                        if (genVerilog)
+                                          t = t + 5;
+                                        return t / 10;
+                                     endactionvalue;
+
+(* synthesize *)
+module sysNestedIfBraces ();
+
+  Reg #(Bit #(4)) cfg_verbosity <- mkReg (1);
+
+  Reg #(Bool) rg_state <- mkReg (False);
+
+  rule rl_display (! rg_state);
+    if (cfg_verbosity != 0)
+      $display ("%0d: display", cur_cycle);
+    rg_state <= True;
+  endrule
+
+  rule rl_finish (rg_state);
+    $finish (0);
+  endrule
+
+endmodule
+

testsuite/bsc.bluesim/misc/misc.exp

@@ -90,3 +90,13 @@ compile_object_pass AVMethBDPIWithReset.bsv
 copy c_func.c.keep c_func.c
 link_objects_pass {} sysAVMethBDPIWithReset {c_func.c}
 }
+
+# GitHub #442: Nested if-else needs braces when possible ambiguity
+# This tests "if (!RST) if (cond) e1 else e2" in the code for
+# executing system tasks.
+if {$ctest == 1} {
+    compile_object_pass NestedIfBraces.bsv
+    link_objects_pass {} sysNestedIfBraces
+    # Test that there were no warnings during C++ compilation
+    compare_file [make_bsc_ccomp_output_name sysNestedIfBraces]
+}

testsuite/bsc.bluesim/misc/sysNestedIfBraces.bsc-ccomp-out.expected

@@ -0,0 +1,4 @@
+Bluesim object created: sysNestedIfBraces.{h,o}
+Bluesim object created: model_sysNestedIfBraces.{h,o}
+Simulation shared library created: sysNestedIfBraces.cexe.so
+Simulation executable created: sysNestedIfBraces.cexe