cross-project-tests/debuginfo-tests/dexter-tests/optnone-fastmath.cpp

   1 // RUN: %dexter --fail-lt 1.0 -w \
   2 // RUN:     --builder 'clang' --debugger 'lldb' \
   3 // RUN:     --cflags "-ffast-math -O2 -g" -- %s
   4 // RUN: %dexter --fail-lt 1.0 -w \
   5 // RUN:     --builder 'clang' --debugger 'lldb' \
   6 // RUN:     --cflags "-ffast-math -O0 -g" -- %s
   7
   8 // REQUIRES: lldb
   9 // UNSUPPORTED: system-windows
  10
  11 //// Check that the debugging experience with __attribute__((optnone)) at O2
  12 //// matches O0. Test scalar floating point arithmetic with -ffast-math.
  13
  14 //// Example of strength reduction.
  15 //// The division by 10.0f can be rewritten as a multiply by 0.1f.
  16 //// A / 10.f ==> A * 0.1f
  17 //// This is safe with fastmath since we treat the two operations
  18 //// as equally precise. However we don't want this to happen
  19 //// with optnone.
  20 __attribute__((optnone))
  21 float test_fdiv(float A) {
  22   float result;
  23   result = A / 10.f;  // DexLabel('fdiv_assign')
  24   return result;      // DexLabel('fdiv_ret')
  25 }
  26 // DexExpectWatchValue('A', 4, on_line=ref('fdiv_assign'))
  27 // DexExpectWatchValue('result', '0.400000006', on_line=ref('fdiv_ret'))
  28
  29 //// (A * B) - (A * C) ==> A * (B - C)
  30 __attribute__((optnone))
  31 float test_distributivity(float A, float B, float C) {
  32   float result;
  33   float op1 = A * B;
  34   float op2 = A * C;    // DexLabel('distributivity_op2')
  35   result = op1 - op2;   // DexLabel('distributivity_result')
  36   return result;        // DexLabel('distributivity_ret')
  37 }
  38 // DexExpectWatchValue('op1', '20', on_line=ref('distributivity_op2'))
  39 // DexExpectWatchValue('op2', '24', on_line=ref('distributivity_result'))
  40 // DexExpectWatchValue('result', '-4', on_line=ref('distributivity_ret'))
  41
  42 //// (A + B) + C  == A + (B + C)
  43 //// therefore, ((A + B) + C) + (A + (B + C)))
  44 //// can be rewritten as
  45 //// 2.0f * ((A + B) + C)
  46 //// Clang is currently unable to spot this optimization
  47 //// opportunity with fastmath.
  48 __attribute__((optnone))
  49 float test_associativity(float A, float B, float C) {
  50   float result;
  51   float op1 = A + B;
  52   float op2 = B + C;
  53   op1 += C;           // DexLabel('associativity_op1')
  54   op2 += A;
  55   result = op1 + op2; // DexLabel('associativity_result')
  56   return result;      // DexLabel('associativity_ret')
  57 }
  58 // DexExpectWatchValue('op1', '9', '15', from_line=ref('associativity_op1'), to_line=ref('associativity_result'))
  59 // DexExpectWatchValue('op2', '11', '15', from_line=ref('associativity_op1'), to_line=ref('associativity_result'))
  60 // DexExpectWatchValue('result', '30', on_line=ref('associativity_ret'))
  61
  62 //// With fastmath, the ordering of instructions doesn't matter
  63 //// since we work under the assumption that there is no loss
  64 //// in precision. This simplifies things for the optimizer which
  65 //// can then decide to reorder instructions and fold
  66 //// redundant operations like this:
  67 ////   A += 5.0f
  68 ////   A -= 5.0f
  69 ////    -->
  70 ////   A
  71 //// This function can be simplified to a return A + B.
  72 __attribute__((optnone))
  73 float test_simplify_fp_operations(float A, float B) {
  74   float result = A + 10.0f; // DexLabel('fp_operations_result')
  75   result += B;              // DexLabel('fp_operations_add')
  76   result -= 10.0f;
  77   return result;            // DexLabel('fp_operations_ret')
  78 }
  79 // DexExpectWatchValue('A', '8.25', on_line=ref('fp_operations_result'))
  80 // DexExpectWatchValue('B', '26.3999996', on_line=ref('fp_operations_result'))
  81 // DexExpectWatchValue('result', '18.25', '44.6500015', '34.6500015', from_line=ref('fp_operations_add'), to_line=ref('fp_operations_ret'))
  82
  83 //// Again, this is a simple return A + B.
  84 //// Clang is unable to spot the opportunity to fold the code sequence.
  85 __attribute__((optnone))
  86 float test_simplify_fp_operations_2(float A, float B, float C) {
  87   float result = A + C; // DexLabel('fp_operations_2_result')
  88   result += B;
  89   result -= C;          // DexLabel('fp_operations_2_subtract')
  90   return result;        // DexLabel('fp_operations_2_ret')
  91 }
  92 // DexExpectWatchValue('A', '9.11999988', on_line=ref('fp_operations_2_result'))
  93 // DexExpectWatchValue('B', '61.050003', on_line=ref('fp_operations_2_result'))
  94 // DexExpectWatchValue('C', '1002.11102', on_line=ref('fp_operations_2_result'))
  95 // DexExpectWatchValue('result', '1072.28101', '70.1699829', from_line=ref('fp_operations_2_subtract'), to_line=ref('fp_operations_2_ret'))
  96
  97 int main() {
  98   float result = test_fdiv(4.0f);
  99   result += test_distributivity(4.0f, 5.0f, 6.0f);
 100   result += test_associativity(4.0f, 5.0f, 6.0f);
 101   result += test_simplify_fp_operations(8.25, result);
 102   result += test_simplify_fp_operations_2(9.12, result, 1002.111);
 103   return static_cast<int>(result);
 104 }