Commit 859bf4d2 authored by Vedant Kumar's avatar Vedant Kumar
Browse files

[Coverage] Emit a gap region to cover switch bodies 

Emit a gap region beginning where the switch body begins. This sets line
execution counts in the areas between non-overlapping cases to 0.

This also removes some special handling of the first case in a switch:
these are now treated like any other case.

This does not resolve an outstanding issue with case statement regions
that do not end when a region is terminated. But it should address
llvm.org/PR44011.

Differential Revision: https://reviews.llvm.org/D70571
parent bf830b01

clang/docs/SourceBasedCodeCoverage.rst

+34 −0
Original line number Diff line number Diff line
@@ -302,3 +302,37 @@ Drawbacks and limitations 
  If the call to ``may_throw()`` propagates an exception into ``f``, the code

  coverage tool may mark the ``return`` statement as executed even though it is

  not. A call to ``longjmp()`` can have similar effects.



Clang implementation details

============================



This section may be of interest to those wishing to understand or improve

the clang code coverage implementation.



Gap regions

-----------



Gap regions are source regions with counts. A reporting tool cannot set a line

execution count to the count from a gap region unless that region is the only

one on a line.



Gap regions are used to eliminate unnatural artifacts in coverage reports, such

as red "unexecuted" highlights present at the end of an otherwise covered line,

or blue "executed" highlights present at the start of a line that is otherwise

not executed.



Switch statements

-----------------



The region mapping for a switch body consists of a gap region that covers the

entire body (starting from the '{' in 'switch (...) {', and terminating where the

last case ends). This gap region has a zero count: this causes "gap" areas in

between case statements, which contain no executable code, to appear uncovered.



When a switch case is visited, the parent region is extended: if the parent

region has no start location, its start location becomes the start of the case.

This is used to support switch statements without a ``CompoundStmt`` body, in

which the switch body and the single case share a count.



For switches with ``CompoundStmt`` bodies, a new region is created at the start

of each switch case.

clang/lib/CodeGen/CoverageMappingGen.cpp

+2 −2
Original line number Diff line number Diff line
@@ -1114,8 +1114,8 @@ struct CounterCoverageMappingBuilder 
        // Make a region for the body of the switch.  If the body starts with

        // a case, that case will reuse this region; otherwise, this covers

        // the unreachable code at the beginning of the switch body.

        size_t Index =

            pushRegion(Counter::getZero(), getStart(CS->body_front()));

        size_t Index = pushRegion(Counter::getZero(), getStart(CS));

        getRegion().setGap(true);

        for (const auto *Child : CS->children())

          Visit(Child);

clang/test/CoverageMapping/switch.cpp

+23 −10
Original line number Diff line number Diff line
@@ -2,11 +2,11 @@ 


                    // CHECK: foo

void foo(int i) {   // CHECK-NEXT: File 0, [[@LINE]]:17 -> [[@LINE+8]]:2 = #0

  switch(i) {

  switch(i) {       // CHECK-NEXT: Gap,File 0, [[@LINE]]:13 -> [[@LINE+4]]:10 = 0

  case 1:           // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+1]]:11 = #2

    return;

  case 2:           // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+1]]:10 = #3

    break;          // CHECK-NEXT: File 0, [[@LINE]]:10 -> [[@LINE+2]]:3 = #1

    break;          // CHECK-NEXT: Gap,File 0, [[@LINE]]:10 -> [[@LINE+2]]:3 = #1

  }

  int x = 0;        // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+1]]:2 = #1

}
@@ -29,7 +29,7 @@ void bar(int i) { // CHECK-NEXT: File 0, [[@LINE]]:17 -> [[@LINE+20]]:2 = #0 
    nop();



  switch (i) {      // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+6]]:2 = #4

    nop();          // CHECK-NEXT: File 0, [[@LINE]]:5 -> [[@LINE+2]]:10 = 0

    nop();          // CHECK-NEXT: Gap,File 0, [[@LINE-1]]:14 -> [[@LINE+2]]:10 = 0

  case 1:           // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+1]]:10 = #7

    nop();

  }
@@ -47,7 +47,7 @@ void baz() { // CHECK-NEXT: File 0, [[@LINE]]:12 -> [[@LINE+5]]:2 = #0 
                    // CHECK-NEXT: main

int main() {        // CHECK-NEXT: File 0, [[@LINE]]:12 -> [[@LINE+35]]:2 = #0

  int i = 0;

  switch(i) {

  switch(i) {       // CHECK-NEXT: Gap,File 0, [[@LINE]]:13 -> [[@LINE+8]]:10 = 0

  case 0:           // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+2]]:10 = #2

    i = 1;

    break;
@@ -58,16 +58,16 @@ int main() { // CHECK-NEXT: File 0, [[@LINE]]:12 -> [[@LINE+35]]:2 = #0 
    break;          // CHECK-NEXT: File 0, [[@LINE]]:10 -> [[@LINE+2]]:3 = #1

  }

  switch(i) {       // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+23]]:2 = #1

  case 0:           // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+2]]:10 = #6

    i = 1;

  case 0:           // CHECK-NEXT: Gap,File 0, [[@LINE-1]]:13 -> [[@LINE+6]]:10 = 0

    i = 1;          // CHECK-NEXT: File 0, [[@LINE-1]]:3 -> [[@LINE+1]]:10 = #6

    break;

  case 1:           // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+3]]:10 = #7

    i = 2;

  default:          // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+1]]:10 = (#7 + #8)

    break;          // CHECK-NEXT: File 0, [[@LINE]]:10 -> [[@LINE+3]]:3 = #5

  }



  switch(i) {       // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+13]]:2 = #5

                    // CHECK-NEXT: File 0, [[@LINE+1]]:3 -> [[@LINE+14]]:2 = #5

  switch(i) {       // CHECK-NEXT: Gap,File 0, [[@LINE]]:13 -> [[@LINE+6]]:11 = 0

  case 1:           // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+5]]:11 = #10

  case 2:           // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+4]]:11 = (#10 + #11)

    i = 11;
@@ -82,10 +82,23 @@ int main() { // CHECK-NEXT: File 0, [[@LINE]]:12 -> [[@LINE+35]]:2 = #0 
  return 0;

}



                     // CHECK: pr44011

int pr44011(int i) { // CHECK-NEXT: File 0, [[@LINE]]:20 -> {{.*}}:2 = #0

  switch (i) {       // CHECK-NEXT: Gap,File 0, [[@LINE]]:14 -> [[@LINE+6]]:13 = 0



  case 1:            // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+1]]:13 = #2

    return 0;



  default:           // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+1]]:13 = #3

    return 1;

  }

} // A region for counter #1 is missing due to the missing return.





// FIXME: End location for "case 1" shouldn't point at the end of the switch.

                         // CHECK: fallthrough

int fallthrough(int i) { // CHECK-NEXT: File 0, [[@LINE]]:24 -> [[@LINE+12]]:2 = #0

  switch(i) {

  switch(i) {       // CHECK-NEXT: Gap,File 0, [[@LINE]]:13 -> [[@LINE+9]]:10 = 0

  case 1:           // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+8]]:10 = #2

    i = 23;

  case 2:           // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+2]]:10 = (#2 + #3)
@@ -101,7 +114,7 @@ int fallthrough(int i) { // CHECK-NEXT: File 0, [[@LINE]]:24 -> [[@LINE+12]]:2 = 
void abort(void) __attribute((noreturn));

                   // CHECK: noret

int noret(int x) { // CHECK-NEXT: File 0, [[@LINE]]:18 -> [[@LINE+9]]:2

  switch (x) {

  switch (x) {     // CHECK-NEXT: Gap,File 0, [[@LINE]]:14 -> [[@LINE+6]]:14 = 0

  default:         // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+1]]:12

    abort();

  case 1:         // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+1]]:13

clang/test/CoverageMapping/switchmacro.c

+1 −1
Original line number Diff line number Diff line
@@ -4,7 +4,7 @@ 


// CHECK: foo

int foo(int i) { // CHECK-NEXT: File 0, [[@LINE]]:16 -> {{[0-9]+}}:2 = #0

  switch (i) {

  switch (i) {   // CHECK-NEXT: Gap,File 0, [[@LINE]]:14 -> {{[0-9]+}}:11 = 0

  default:       // CHECK-NEXT: File 0, [[@LINE]]:3 -> {{[0-9]+}}:11 = #2

    if (i == 1)  // CHECK-NEXT: File 0, [[@LINE]]:9 -> [[@LINE]]:15 = #2

      return 0;  // CHECK: File 0, [[@LINE]]:7 -> [[@LINE]]:15 = #3