From 8e3a73448c5ddfa4be3871d7f4fd80281a7549f4 Mon Sep 17 00:00:00 2001
From: Xavier Leroy <xavier.leroy@college-de-france.fr>
Date: Fri, 31 May 2019 19:15:19 +0200
Subject: If-conversion optimization

Extends the instruction selection pass with an if-conversion optimization:
some if/then/else statements are converted into "select" operations,
which in turn can be compiled down to branchless instruction sequences
if the target architecture supports them.

The statements that are converted are of the form

        if (cond) { x = a1; } else { x = a2; }
        if (cond) { x = a1; }
        if (cond) { /*skip*/; } else { x = a2; }

where a1, a2 are "safe" expressions, containing no operations that can
fail at run-time, such as memory loads or integer divisions.

A heuristic in backend/Selectionaux.ml controls when the optimization occurs,
depending on command-line flags and the complexity of the "then" and "else"
branches.
---
 test/regression/ifconv.c | 129 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 129 insertions(+)
 create mode 100644 test/regression/ifconv.c

(limited to 'test/regression/ifconv.c')

diff --git a/test/regression/ifconv.c b/test/regression/ifconv.c
new file mode 100644
index 00000000..dcbf43e5
--- /dev/null
+++ b/test/regression/ifconv.c
@@ -0,0 +1,129 @@
+#include <stdio.h>
+
+/* Several equivalent forms that should be turned into cmov */
+
+int test1(int x, int y, int a, int b)
+{
+  return x < y ? a : b;
+}
+
+int test2(int x, int y, int a, int b)
+{
+  int r;
+  if (x < y) { r = a; } else { r = b; }
+  return r;
+}
+
+int test3(int x, int y, int a, int b)
+{
+  int r = b;
+  if (x < y) { r = a; }
+  return r;
+}
+
+int test4(int x, int y, int a, int b)
+{
+  int r = a;
+  if (x < y) { /*skip*/; } else { r = b; }
+  return r;
+}
+
+/* A more advanced example */
+
+int test5(int x, int y, int a)
+{
+  return x < y ? a + 1 : a - 1;
+}
+
+/* Unsafe operations should not be turned into cmov */
+
+int test6(int * p)
+{
+  return p == NULL ? 0 : *p + 10;
+}
+
+int test7(int a, int b)
+{
+  return b == 0 ? -1 : a / b;
+}
+
+/* Very large operations should not be turned into cmov */
+
+int test8(int a)
+{
+  return a == 0 ? 0 : a*a*a*a - 2*a*a*a + 10*a*a + 42*a - 123;
+}
+
+/* Some examples with 64-bit integers */
+
+long long ltest1(int x, int y, long long a, long long b)
+{
+  return x < y ? a + 1 : b >> 2;
+}
+
+/* Some examples with floating-point */
+
+double dmax(double x, double y)
+{
+  return x >= y ? x : y;
+}
+
+double dabs(double x)
+{
+  return x < 0.0 ? -x : x;
+}
+
+float smin(float x, float y)
+{
+  return x <= y ? x : y;
+}
+
+float sdoz(float x, float y)
+{
+  return x >= y ? x - y : 0.0f;
+}
+
+/* Test harness */
+
+#define TESTI(call) printf(#call " = %d\n", call)
+#define TESTL(call) printf(#call " = %lld\n", call)
+#define TESTF(call) printf(#call " = %f\n", call)
+
+
+int main()
+{
+  int i = 1234;
+  TESTI(test1(0,1,12,34));
+  TESTI(test1(1,0,45,67));
+  TESTI(test2(0,1,12,34));
+  TESTI(test2(1,0,45,67));
+  TESTI(test3(0,1,12,34));
+  TESTI(test3(1,0,45,67));
+  TESTI(test4(0,1,12,34));
+  TESTI(test4(1,0,45,67));
+  TESTI(test5(0,1,12));
+  TESTI(test5(1,0,45));
+  TESTI(test6(NULL));
+  TESTI(test6(&i));
+  TESTI(test7(1,0));
+  TESTI(test7(-100,4));
+  TESTI(test8(0));
+  TESTI(test8(1));
+
+  TESTL(ltest1(-1, 0, 123LL, 456LL));
+  TESTL(ltest1(1, 0, 123LL, 456LL));
+
+  TESTF(dmax(0.0, 3.14));
+  TESTF(dmax(1.0, -2.718));
+
+  TESTF(dabs(1.0));
+  TESTF(dabs(-2.718));
+
+  TESTF(smin(0.0, 3.14));
+  TESTF(smin(1.0, -2.718));
+
+  TESTF(sdoz(1.0, 0.5));
+  TESTF(sdoz(0.0, 3.14));
+
+  return 0;
+}
-- 
cgit