middle-end: reorder masking priority of math functions

Given the categorization of math built-in functions as `ECF_CONST',
when if-converting their uses, their calls are not masked and are thus
called with an all-true predicate.

This, however, is not appropriate where built-ins have library
equivalents, wherein they may exhibit highly architecture-specific
behaviors. For example, vectorized implementations may delegate the
computation of values outside a certain acceptable numerical range to
special (non-vectorized) routines which considerably slow down
computation.

As numerical simulation programs often do bounds check on input values
prior to math calls, conditionally assigning default output values for
out-of-bounds input and skipping the math call altogether, these
fallback implementations should seldom be called in the execution of
vectorized code.  If, however, we don't apply any masking to these
math functions, we end up effectively executing both if and else
branches for these values, leading to considerable performance
degradation on scientific workloads.

We therefore invert the order of handling of math function calls in
`if_convertible_stmt_p' to prioritize the handling of their
library-provided implementations over the equivalent internal function.

gcc/ChangeLog:

	* tree-if-conv.cc (if_convertible_stmt_p): Check for explicit
	function declaration before IFN fallback.

gcc/testsuite/ChangeLog:

	* gcc.dg/vect/vect-fncall-mask-math.c: New.

diff --git a/gcc/testsuite/gcc.dg/vect/vect-fncall-mask-math.c b/gcc/testsuite/gcc.dg/vect/vect-fncall-mask-math.c
new file mode 100644 (file)
index 0000000..15e22da
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-fncall-mask-math.c
@@ -0,0 +1,33 @@
+/* Test the correct application of masking to autovectorized math function calls.
+   Test is currently set to xfail pending the release of the relevant lmvec
+   support. */
+/* { dg-do compile { target { aarch64*-*-* } } } */
+/* { dg-additional-options "-march=armv8.2-a+sve -fdump-tree-ifcvt-raw -Ofast" { target { aarch64*-*-* } } } */
+
+#include <math.h>
+
+const int N = 20;
+const float lim = 101.0;
+const float cst =  -1.0;
+float tot =   0.0;
+
+float b[20];
+float a[20] = { [0 ... 9] = 1.7014118e39, /* If branch. */
+               [10 ... 19] = 100.0 };    /* Else branch.  */
+
+int main (void)
+{
+  #pragma omp simd
+  for (int i = 0; i < N; i += 1)
+    {
+      if (a[i] > lim)
+       b[i] = cst;
+      else
+       b[i] = expf (a[i]);
+      tot += b[i];
+    }
+  return (0);
+}
+
+/* { dg-final { scan-tree-dump-not { gimple_call <expf, _2, _1>} ifcvt { xfail { aarch64*-*-* } } } } */
+/* { dg-final { scan-tree-dump { gimple_call <.MASK_CALL, _2, expf, _1, _30>} ifcvt { xfail { aarch64*-*-* } } } } */

diff --git a/gcc/tree-if-conv.cc b/gcc/tree-if-conv.cc
index 3b04d1e8d34fa43639bdac8c00826eed2d9998bb..90c754a48147c7eb29e65411e0456516b404fd5a 100644 (file)
--- a/gcc/tree-if-conv.cc
+++ b/gcc/tree-if-conv.cc
@@ -1133,15 +1133,6 @@ if_convertible_stmt_p (gimple *stmt, vec<data_reference_p> refs)
 
     case GIMPLE_CALL:
       {
-       /* There are some IFN_s that are used to replace builtins but have the
-          same semantics.  Even if MASK_CALL cannot handle them vectorable_call
-          will insert the proper selection, so do not block conversion.  */
-       int flags = gimple_call_flags (stmt);
-       if ((flags & ECF_CONST)
-           && !(flags & ECF_LOOPING_CONST_OR_PURE)
-           && gimple_call_combined_fn (stmt) != CFN_LAST)
-         return true;
-
        tree fndecl = gimple_call_fndecl (stmt);
        if (fndecl)
          {
@@ -1160,6 +1151,15 @@ if_convertible_stmt_p (gimple *stmt, vec<data_reference_p> refs)
                  }
          }
 
+       /* There are some IFN_s that are used to replace builtins but have the
+          same semantics.  Even if MASK_CALL cannot handle them vectorable_call
+          will insert the proper selection, so do not block conversion.  */
+       int flags = gimple_call_flags (stmt);
+       if ((flags & ECF_CONST)
+           && !(flags & ECF_LOOPING_CONST_OR_PURE)
+           && gimple_call_combined_fn (stmt) != CFN_LAST)
+         return true;
+
        return false;
       }