[cost] Report the biggest cost in function

Summary:
In the previous report, it reported the first cost of node that exceeds a threshold.  However, this
may hide a bigger cost of node that appears later.  This diff changes this to report the biggest
cost of node among the costs exceeding the threshold.

Reviewed By: ezgicicek

Differential Revision: D20116162

fbshipit-source-id: 06199fb46

infer/src/cost/cost.ml

@@ -188,6 +188,9 @@ module WorstCaseCost = struct
           | Some (ThresholdReports.Threshold threshold), Some cost
             when should_report_cost cost ~threshold ->
               Some (ThresholdReports.ReportOn {location= InstrCFG.Node.loc instr_node; cost})
+          | Some (ThresholdReports.ReportOn {cost= prev}), Some cost
+            when (not (BasicCost.is_top cost)) && BasicCost.compare_by_degree prev cost < 0 ->
+              Some (ThresholdReports.ReportOn {location= InstrCFG.Node.loc instr_node; cost})
           | _ ->
               threshold_or_report_opt )
         reports costs

infer/tests/codetoanalyze/java/performance/Cost_test.java

@@ -210,6 +210,11 @@ public class Cost_test {
   void mult_symbols_quadratic(int x, int y) {
     for (int i = 0; i < x * y; i++) {}
   }
+
+  void call_mult_symbold_quadratic(int n) {
+    for (int i = 0; i < n; i++) {}
+    mult_symbols_quadratic(n, n);
+  }
 }
 
 class CloneTest {

infer/tests/codetoanalyze/java/performance/issues.exp

@@ -93,6 +93,8 @@ codetoanalyze/java/performance/Continue.java, codetoanalyze.java.performance.Con
 codetoanalyze/java/performance/Cost_test.java, codetoanalyze.java.performance.Cost_test.FN_loop2(int):int, 0, EXPENSIVE_EXECUTION_TIME, no_bucket, ERROR, [with estimated cost 2 + 13 ⋅ k, O(k), degree = 1,{k},Loop at line 92]
 codetoanalyze/java/performance/Cost_test.java, codetoanalyze.java.performance.Cost_test.band_constant(int):void, 0, EXPENSIVE_EXECUTION_TIME, no_bucket, ERROR, [with estimated cost 1277, O(1), degree = 0]
 codetoanalyze/java/performance/Cost_test.java, codetoanalyze.java.performance.Cost_test.call_inputstream_read_linear(java.io.InputStream):void, 3, EXPENSIVE_EXECUTION_TIME, no_bucket, ERROR, [with estimated cost 27304, O(1), degree = 0]
+codetoanalyze/java/performance/Cost_test.java, codetoanalyze.java.performance.Cost_test.call_mult_symbold_quadratic(int):void, 1, EXPENSIVE_EXECUTION_TIME, no_bucket, ERROR, [with estimated cost 14 + 5 ⋅ n + 6 ⋅ n², O(n²), degree = 2,{n},call to void Cost_test.mult_symbols_quadratic(int,int),Loop at line 211,{n},call to void Cost_test.mult_symbols_quadratic(int,int),Loop at line 211,{n},Loop at line 215]
+codetoanalyze/java/performance/Cost_test.java, codetoanalyze.java.performance.Cost_test.call_mult_symbold_quadratic(int):void, 1, INTEGER_OVERFLOW_L5, no_bucket, ERROR, [Assignment,Call,<LHS trace>,Assignment,Binary operation: ([0, +oo] + 1):signed32 by call to `void Cost_test.mult_symbols_quadratic(int,int)` ]
 codetoanalyze/java/performance/Cost_test.java, codetoanalyze.java.performance.Cost_test.ignore_boolean_symbols_linear(boolean,int):void, 0, EXPENSIVE_EXECUTION_TIME, no_bucket, ERROR, [with estimated cost 2 + 6 ⋅ n + 2 ⋅ (1+max(0, n)), O(n), degree = 1,{1+max(0, n)},Loop at line 135,{n},Loop at line 135]
 codetoanalyze/java/performance/Cost_test.java, codetoanalyze.java.performance.Cost_test.loop0_bad():int, 0, EXPENSIVE_EXECUTION_TIME, no_bucket, ERROR, [with estimated cost 1202, O(1), degree = 0]
 codetoanalyze/java/performance/Cost_test.java, codetoanalyze.java.performance.Cost_test.loop1_bad():int, 1, EXPENSIVE_EXECUTION_TIME, no_bucket, ERROR, [with estimated cost 1303, O(1), degree = 0]