[flang/flang-rt] Adding support of RAND, IRAND and SRAND intrinsics

[JDPailleux]

This PR adds support of RAND, IRAND and SRAND intrinsics in Flang, which are part of the GNU extension.
These intrinsics are used in the following benchmark: floatingspeed

[llvmbot]

@llvm/pr-subscribers-flang-semantics

@llvm/pr-subscribers-flang-fir-hlfir

Author: Jean-Didier PAILLEUX (JDPailleux)

Changes

This PR adds support of RAND, IRAND and SRAND intrinsics in Flang, which are part of the GNU extension.
These intrinsics are used in the following benchmark: floatingspeed

---

Full diff: https://github.com/llvm/llvm-project/pull/166780.diff

4 Files Affected:

• (modified) flang-rt/lib/runtime/extensions.cpp (+23)
• (modified) flang/docs/Intrinsics.md (+43)
• (modified) flang/include/flang/Runtime/extensions.h (+9)
• (added) flang/test/Lower/Intrinsics/rand.f90 (+41)

diff --git a/flang-rt/lib/runtime/extensions.cpp b/flang-rt/lib/runtime/extensions.cpp
index 19e75143705ab..366406d2a71e4 100644
--- a/flang-rt/lib/runtime/extensions.cpp
+++ b/flang-rt/lib/runtime/extensions.cpp
@@ -398,6 +398,29 @@ std::int64_t RTNAME(time)() { return time(nullptr); }
 // MCLOCK: returns accumulated CPU time in ticks
 std::int32_t FORTRAN_PROCEDURE_NAME(mclock)() { return std::clock(); }
 
+// IRAND(I)
+int FORTRAN_PROCEDURE_NAME(irand)(int i) {
+  switch (i) {
+  case 0:
+    break;
+  case 1:
+    FORTRAN_PROCEDURE_NAME(srand)(0);
+    break;
+  default:
+    FORTRAN_PROCEDURE_NAME(srand)(i);
+    break;
+  }
+  return rand();
+}
+
+// RAND(I)
+float FORTRAN_PROCEDURE_NAME(rand)(int i) {
+  return (float)(FORTRAN_PROCEDURE_NAME(irand)(i));
+}
+
+// SRAND(SEED)
+void FORTRAN_PROCEDURE_NAME(srand)(int seed) { srand(seed); }
+
 // Extension procedures related to I/O
 
 namespace io {
diff --git a/flang/docs/Intrinsics.md b/flang/docs/Intrinsics.md
index bfda5f3253a68..af20892edd201 100644
--- a/flang/docs/Intrinsics.md
+++ b/flang/docs/Intrinsics.md
@@ -1379,3 +1379,46 @@ This is prefixed by `STRING`, a colon and a space.
 - **Standard:** GNU extension
 - **Class:** subroutine
 - **Syntax:** `CALL PERROR(STRING)`
+
+
+### Non-Standard Intrinsics: SRAND
+
+#### Description
+`SAND` reinitializes the pseudo-random number generator called by `RAND` and `IRAND`.
+The new seed used by the generator is specified by the required argument `SEED`.
+
+#### Usage and Info
+
+- **Standard:** GNU extension
+- **Class:** Subroutine
+- **Syntax:** `CALL SRAND(SEED)`
+
+### Non-Standard Intrinsics: IRAND
+
+#### Description
+`IRAND(FLAG)` returns a pseudo-random number from a uniform distribution between 0 and 1.
+If `FLAG` is 0, the next number in the current sequence is returned;
+If `FLAG` is 1, the generator is restarted by `CALL SRAND(0)`;
+If `FLAG` has any other value, it is used as a new seed with `SRAND`.
+The return value is of `INTEGER` type of kind 4.
+
+#### Usage and Info
+
+- **Standard:** GNU extension
+- **Class:** function
+- **Syntax:** `RESULT = IRAND(I)`
+
+### Non-Standard Intrinsics: RAND
+
+#### Description
+`RAND(FLAG)` returns a pseudo-random number from a uniform distribution between 0 and 1.
+If `FLAG` is 0, the next number in the current sequence is returned;
+If `FLAG` is 1, the generator is restarted by `CALL SRAND(0)`;
+If `FLAG` has any other value, it is used as a new seed with `SRAND`.
+The return value is of `REAL` type with the default kind.
+
+#### Usage and Info
+
+- **Standard:** GNU extension
+- **Class:** function
+- **Syntax:** `RESULT = RAND(I)`
diff --git a/flang/include/flang/Runtime/extensions.h b/flang/include/flang/Runtime/extensions.h
index 9fd3e118a0f22..73a458b26e2d7 100644
--- a/flang/include/flang/Runtime/extensions.h
+++ b/flang/include/flang/Runtime/extensions.h
@@ -101,5 +101,14 @@ int FORTRAN_PROCEDURE_NAME(mclock)();
 float FORTRAN_PROCEDURE_NAME(secnds)(float *refTime);
 float RTNAME(Secnds)(float *refTime, const char *sourceFile, int line);
 
+// GNU extension function IRAND(I)
+int FORTRAN_PROCEDURE_NAME(irand)(int i = 0);
+
+// GNU extension function RAND(I)
+float FORTRAN_PROCEDURE_NAME(rand)(int i = 0);
+
+// GNU extension subroutine SRAND(SEED)
+void FORTRAN_PROCEDURE_NAME(srand)(int seed);
+
 } // extern "C"
 #endif // FORTRAN_RUNTIME_EXTENSIONS_H_
diff --git a/flang/test/Lower/Intrinsics/rand.f90 b/flang/test/Lower/Intrinsics/rand.f90
new file mode 100644
index 0000000000000..488242fb9180d
--- /dev/null
+++ b/flang/test/Lower/Intrinsics/rand.f90
@@ -0,0 +1,41 @@
+! RUN: bbc -emit-hlfir %s -o - | FileCheck --check-prefixes=CHECK %s
+! RUN: %flang_fc1 -emit-hlfir %s -o - | FileCheck --check-prefixes=CHECK %s
+
+! CHECK-LABEL: func @_QPtest_srand(
+subroutine test_srand()
+  integer :: seed = 0
+  call srand(seed)
+  ! CHECK: %[[VAL_0:.*]] = fir.address_of(@_QFtest_srandEseed) : !fir.ref<i32> 
+  ! CHECK: %[[VAL_1:.*]]:2 = hlfir.declare %[[VAL_0]] {uniq_name = "_QFtest_srandEseed"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+  ! CHECK: fir.call @_QPsrand(%[[VAL_1]]#0) fastmath<contract> : (!fir.ref<i32>) -> () 
+  ! CHECK: return
+end subroutine test_srand
+
+! CHECK-LABEL: func @_QPtest_irand(
+subroutine test_irand()
+  integer :: seed = 0
+  integer :: result
+  result = irand(seed)
+  ! CHECK: %[[VAL_0:.*]] = fir.alloca i32 {bindc_name = "result", uniq_name = "_QFtest_irandEresult"} 
+  ! CHECK: %[[VAL_1:.*]]:2 = hlfir.declare %[[VAL_0]] {uniq_name = "_QFtest_irandEresult"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+  ! CHECK: %[[VAL_2:.*]] = fir.address_of(@_QFtest_irandEseed) : !fir.ref<i32> 
+  ! CHECK: %[[VAL_3:.*]]:2 = hlfir.declare %[[VAL_2]] {uniq_name = "_QFtest_irandEseed"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+  ! CHECK: %[[VAL_4:.*]] = fir.call @_QPirand(%[[VAL_3]]#0) fastmath<contract> : (!fir.ref<i32>) -> i32
+  ! CHECK: hlfir.assign %[[VAL_4]] to %[[VAL_1]]#0 : i32, !fir.ref<i32>
+  ! CHECK: return
+end subroutine test_irand
+
+! CHECK-LABEL: func @_QPtest_rand(
+subroutine test_rand()
+  integer :: seed = 0
+  real :: result
+  result = rand(seed)
+  ! CHECK: %[[VAL_0:.*]] = fir.alloca f32 {bindc_name = "result", uniq_name = "_QFtest_randEresult"} 
+  ! CHECK: %[[VAL_1:.*]]:2 = hlfir.declare %[[VAL_0]] {uniq_name = "_QFtest_randEresult"} : (!fir.ref<f32>) -> (!fir.ref<f32>, !fir.ref<f32>)
+  ! CHECK: %[[VAL_2:.*]] = fir.address_of(@_QFtest_randEseed) : !fir.ref<i32> 
+  ! CHECK: %[[VAL_3:.*]]:2 = hlfir.declare %[[VAL_2]] {uniq_name = "_QFtest_randEseed"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+  ! CHECK: %[[VAL_4:.*]] = fir.call @_QPrand(%[[VAL_3]]#0) fastmath<contract> : (!fir.ref<i32>) -> f32
+  ! CHECK: hlfir.assign %[[VAL_4]] to %[[VAL_1]]#0 : f32, !fir.ref<f32>
+  ! CHECK: return
+end subroutine test_rand
+

[tblah]

LGTM with the typo fixed

[JDPailleux]

Thanks

[kkwli]

irand returns an integer. Is it only 0 or 1?

[JDPailleux]

This is another copy past typo. It returns an integer between 0 and a system-dependent limit

[kkwli]

Is it really "system-dependent limit"? gfortran's rand returns random numbers between 0 and 1.

[kkwli]

I get the same random number with rand(0).

$ cat rand.f90
do i=1, 5
  print *, rand(0)
enddo
end

$ bin/flang -frtlib-add-rpath rand.f90

$ a.out
 1.9679691E+09
 1.9679691E+09
 1.9679691E+09
 1.9679691E+09
 1.9679691E+09

gfortran gives the following output:

$ gfortran rand.f90
$ a.out
   7.62939453E-06
  0.131537676    
  0.755605221    
  0.458650112    
  0.532767057    

[JDPailleux]

Hello, here is an update for RAND and IRAND.
I based the implementation of the GNU extension and no longer naively use the rand() and srand() functions.

[github-actions]

🐧 Linux x64 Test Results

• 4061 tests passed
• 202 tests skipped