tree-optimization/107647 - avoid FMA from SLP with -ffp-contract=off
Commit Message
Only with -ffp-contract=fast we can synthesize FMA operations like
vfmaddsub231ps, so properly guard the transform in SLP pattern
detection.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
PR tree-optimization/107647
* tree-vect-slp-patterns.cc (addsub_pattern::recognize): Only
allow FMA generation with -ffp-contract=fast for FP types.
(complex_mul_pattern::matches): Likewise.
* gcc.target/i386/pr107647.c: New testcase.
---
gcc/testsuite/gcc.target/i386/pr107647.c | 17 +++++++++++++++++
gcc/tree-vect-slp-patterns.cc | 15 +++++++++++----
2 files changed, 28 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/i386/pr107647.c
new file mode 100644
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ffp-contract=off -mavx2 -mfma" } */
+
+void cscal(int n, float da_r, float *x)
+{
+ for (int i = 0; i < n; i += 4)
+ {
+ float temp0 = da_r * x[i] - x[i+1];
+ float temp1 = da_r * x[i+2] - x[i+3];
+ x[i+1] = da_r * x[i+1] + x[i];
+ x[i+3] = da_r * x[i+3] + x[i+2];
+ x[i] = temp0;
+ x[i+2] = temp1;
+ }
+}
+
+/* { dg-final { scan-assembler-not "fma" } } */
@@ -1035,8 +1035,11 @@ complex_mul_pattern::matches (complex_operation_t op,
auto_vec<slp_tree> left_op, right_op;
slp_tree add0 = NULL;
- /* Check if we may be a multiply add. */
+ /* Check if we may be a multiply add. It's only valid to form FMAs
+ with -ffp-contract=fast. */
if (!mul0
+ && (flag_fp_contract_mode == FP_CONTRACT_FAST
+ || !FLOAT_TYPE_P (SLP_TREE_VECTYPE (l0node[0])))
&& vect_match_expression_p (l0node[0], PLUS_EXPR))
{
auto vals = SLP_TREE_CHILDREN (l0node[0]);
@@ -1501,9 +1504,13 @@ addsub_pattern::recognize (slp_tree_to_load_perm_map_t *,
}
/* Now we have either { -, +, -, + ... } (!l0add_p) or { +, -, +, - ... }
- (l0add_p), see whether we have FMA variants. */
- if (!l0add_p
- && vect_match_expression_p (SLP_TREE_CHILDREN (l0node)[0], MULT_EXPR))
+ (l0add_p), see whether we have FMA variants. We can only form FMAs
+ if allowed via -ffp-contract=fast. */
+ if (flag_fp_contract_mode != FP_CONTRACT_FAST
+ && FLOAT_TYPE_P (SLP_TREE_VECTYPE (l0node)))
+ ;
+ else if (!l0add_p
+ && vect_match_expression_p (SLP_TREE_CHILDREN (l0node)[0], MULT_EXPR))
{
/* (c * d) -+ a */
if (vect_pattern_validate_optab (IFN_VEC_FMADDSUB, node))