This is my proposed fix to PR middle-end/87256 where synth_mult takes an
unreasonable amount of CPU time determining an optimal sequence of
instructions to perform multiplications by (large) integer constants on
hppa.
One workaround, proposed in bugzilla, is to increase the hash table used
to cache/reuse intermediate results. This helps but is a workaround for
the (more subtle) underlying problem.
The real issue is that the hppa_rtx_costs function is providing wildly
inaccurate values (estimates) to the middle-end. For example, (p*q)+(r*s)
would appear to be cheaper than a single multiplication. Another
example is that "(ashiftrt:di regA regB)" is claimed to be only
COST_N_INSNS(1) when in fact the hppa backend actually generates:
ashrdi: ldi 32,%r28
and %r24,%r28,%r28
comib,= 0,%r28,.L6
mtsar %r24
subi 31,%r24,%r24
extrs %r25,0,1,%r28
mtsar %r24
bv %r0(%r2)
vextrs %r25,32,%r29
.L6:uaddcm %r0,%r24,%r28
vshd %r0,%r26,%r29
subi 31,%r28,%r28
mtsar %r28
zdep %r25,30,31,%r19
subi 31,%r24,%r24
zvdep %r19,32,%r19
mtsar %r24
or %r19,%r29,%r29
bv %r0(%r2)
vextrs %r25,32,%r28
which is slightly more than a single instruction.
It turns out that simply tightening up the logic in hppa_rtx_costs to
return more reasonable values, dramatically reduces the number of recursive
invocations in synth_mult for the test case in PR87256, and presumably
also produces faster code (that should be observable in benchmarks).
Unfortunately, once again this has only be tested via cross-compilers
to hppa-unknown-linux-gnu and hppa64-unknown-linux-gnu hosted on
x86_64-pc-linux-gnu, but I can confirm cross-compilation is much faster.
Many thanks in advance to anyone who can bootstrap and regression test
this on real hardware. In an ideal world, changes to rtx_costs should
be pretty safe, this function can't introduce any bugs, only expose those
are already present (but possibly latent) elsewhere in the compiler. Ha.
2020-08-21 Roger Sayle
gcc/ChangeLog
PR middle-end/87256
* config/pa/pa.c (hppa_rtx_costs_shadd_p): New helper function
to check for coefficients supported by shNadd and shladd,l.
(hppa_rtx_costs): Rewrite to avoid using estimates based upon
FACTOR and enable recursing deeper into RTL expressions.
Thanks again.
Roger
--
Roger Sayle
NextMove Software
Cambridge, UK
diff --git a/gcc/config/pa/pa.c b/gcc/config/pa/pa.c
index 07d3287..cc876e6 100644
--- a/gcc/config/pa/pa.c
+++ b/gcc/config/pa/pa.c
@@ -1492,6 +1492,33 @@ hppa_address_cost (rtx X, machine_mode mode
ATTRIBUTE_UNUSED,
}
}
+/* Return true if X represents a (possibly non-canonical) shNadd pattern.
+ The machine mode of X is known to be SImode or DImode. */
+
+static bool
+hppa_rtx_costs_shadd_p (rtx x)
+{
+ if (GET_CODE (x) != PLUS
+ || !REG_P (XEXP (x, 1)))
+return false;
+ rtx op0 = XEXP (x, 0);
+ if (GET_CODE (op0) == ASHIFT
+ && CONST_INT_P (XEXP (op0, 1))
+ && REG_P (XEXP (op0, 0)))
+{
+ unsigned HOST_WIDE_INT x = UINTVAL (XEXP (op0, 1));
+ return x == 1 || x == 2 || x == 3;
+}
+ if (GET_CODE (op0) == MULT
+ && CONST_INT_P (XEXP (op0, 1))
+ && REG_P (XEXP (op0, 0)))
+{
+ unsigned HOST_WIDE_INT x = UINTVAL (XEXP (op0, 1));
+ return x == 2 || x == 4 || x == 8;
+}
+ return false;
+}
+
/* Compute a (partial) cost for rtx X. Return true if the complete
cost has been computed, and false if subexpressions should be
scanned. In either case, *TOTAL contains the cost result. */
@@ -1499,15 +1526,16 @@ hppa_address_cost (rtx X, machine_mode mode
ATTRIBUTE_UNUSED,
static bool
hppa_rtx_costs (rtx x, machine_mode mode, int outer_code,
int opno ATTRIBUTE_UNUSED,
- int *total, bool speed ATTRIBUTE_UNUSED)
+ int *total, bool speed)
{
- int factor;
int code = GET_CODE (x);
switch (code)
{
case CONST_INT:
- if (INTVAL (x) == 0)
+ if (outer_code == SET)
+ *total = COSTS_N_INSNS (1);
+ else if (INTVAL (x) == 0)
*total = 0;
else if (INT_14_BITS (x))
*total = 1;
@@ -1537,25 +1565,28 @@ hppa_rtx_costs (rtx x, machine_mode mode, int
outer_code,
if (GET_MODE_CLASS (mode) == MODE_FLOAT)
{
*total = COSTS_N_INSNS (3);
- return true;
}
-
- /* A mode size N times larger than SImode needs O(N*N) more insns. */
- factor = GET_MODE_SIZE (mode) / 4;
- if (factor == 0)
- factor = 1;
-
- if (TARGET_PA_11 && !TARGET_DISABLE_FPREGS && !TARGET_SOFT_FLOAT)
- *total = factor * factor * COSTS_N_INSNS (8);
+ else if (mode == DImode)
+ {
+ if (TARGET_PA_11 && !TARGET_DISABLE_FPREGS && !TARGET_SOFT_FLOAT)
+ *total = COSTS_N_INSNS (32);
+ else
+ *total = COSTS_N_INSNS (80);
+ }
