This patch resolves PR tree-optimization/104420, which is a P1 regression
where, as observed by Jakub Jelinek, the conditions for constant folding
x*0.0 are incorrect (following my patch for PR tree-optimization/96392).
The multiplication x*0.0 may yield a negative zero result, -0.0, if X is
negative (not just if x may be negative zero). Hence (without -ffast-math)
(int)x*0.0 can't be optimized to 0.0, but (unsigned)x*0.0 can be constant
folded. This adds a bunch of test cases to confirm the desired behaviour,
and removes an incorrect test from gcc.dg/pr96392.c which checked for the
wrong behaviour.
This patch has been tested on x86_64-pc-linux-gnu with make bootstrap and
make -k check no new failures. Ok for mainline?
2022-02-08 Roger Sayle <ro...@nextmovesoftware.com>
gcc/ChangeLog
PR tree-optimization/104420
* match.pd (mult @0 real_zerop): Tweak conditions for constant
folding X*0.0 (or X*-0.0) to HONOR_SIGNED_ZEROS when appropriate.
gcc/testsuite/ChangeLog
PR tree-optimization/104420
* gcc.dg/pr104420-1.c: New test case.
* gcc.dg/pr104420-2.c: New test case.
* gcc.dg/pr104420-3.c: New test case.
* gcc.dg/pr104420-4.c: New test case.
* gcc.dg/pr96392.c: Remove incorrect test.
Thanks in advance (and sorry for the breakage/thinko).
Roger
--
diff --git a/gcc/match.pd b/gcc/match.pd
index 7bbb801..4fe5909 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -262,8 +262,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(mult @0 real_zerop@1)
(if (!tree_expr_maybe_nan_p (@0)
&& (!HONOR_NANS (type) || !tree_expr_maybe_infinite_p (@0))
- && !tree_expr_maybe_real_minus_zero_p (@0)
- && !tree_expr_maybe_real_minus_zero_p (@1))
+ && (!HONOR_SIGNED_ZEROS (type) || tree_expr_nonnegative_p (@0)))
@1))
/* In IEEE floating point, x*1 is not equivalent to x for snans.
diff --git a/gcc/testsuite/gcc.dg/pr104420-1.c
b/gcc/testsuite/gcc.dg/pr104420-1.c
new file mode 100644
index 0000000..48385fa
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr104420-1.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-add-options ieee } */
+
+double f(int a)
+{
+ return a * 0.0;
+}
+
+/* { dg-final { scan-tree-dump " \\\* 0.0" "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/pr104420-2.c
b/gcc/testsuite/gcc.dg/pr104420-2.c
new file mode 100644
index 0000000..49d0189
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr104420-2.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-add-options ieee } */
+
+double f(int a)
+{
+ return a * -0.0;
+}
+
+/* { dg-final { scan-tree-dump " \\\* -0.0" "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/pr104420-3.c
b/gcc/testsuite/gcc.dg/pr104420-3.c
new file mode 100644
index 0000000..962dfff
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr104420-3.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-add-options ieee } */
+
+double f(unsigned int a)
+{
+ return a * 0.0;
+}
+
+/* { dg-final { scan-tree-dump "return 0.0" "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/pr104420-4.c
b/gcc/testsuite/gcc.dg/pr104420-4.c
new file mode 100644
index 0000000..95ed0cc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr104420-4.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-add-options ieee } */
+
+double f(unsigned int a)
+{
+ return a * -0.0;
+}
+
+/* { dg-final { scan-tree-dump "return -0.0" "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/pr96392.c b/gcc/testsuite/gcc.dg/pr96392.c
index 662bacb..fb7de21 100644
--- a/gcc/testsuite/gcc.dg/pr96392.c
+++ b/gcc/testsuite/gcc.dg/pr96392.c
@@ -12,11 +12,6 @@ double sub0(int x)
return x - 0.0;
}
-double mult0(int x)
-{
- return 0.0 * x;
-}
-
double negate(int x)
{
return 0.0 - x;
@@ -29,5 +24,4 @@ double subtract(int x)
/* { dg-final { scan-tree-dump-not " \\+ " "optimized" } } */
/* { dg-final { scan-tree-dump-not " \\- " "optimized" } } */
-/* { dg-final { scan-tree-dump-not " \\* " "optimized" } } */
