Per Aldy's excellent, but tough to follow analysis in PR 103226, this
patch fixes the bfin-elf regression.
In simplest terms the doloop patterns on this port may clobber the
condition code register, but they do not expose that until after
register allocation. That would be fine, except that other patterns
have exposed CC earlier. As a result the dataflow, particularly for CC,
is incorrect.
This leads the register allocators to assume that a value in CC outside
the loop is still valid inside the loop when in fact, the value has been
clobbered. This is what caused pr80974 to start failing.
With this fix, not only do we fix the pr80974 regression, but we fix ~20
other execution failures in the port. It also reduces test time for the
port from ~90 minutes to ~60 minutes.
Committed to the trunk,
Jeff
commit 7950c96ca667ddaab9d6e894da3958ebc2e2dccb
Author: Jeff Law <jeffreya...@gmail.com>
Date: Sat Nov 20 11:20:07 2021 -0500
Clobber the condition code in the bfin doloop patterns
Per Aldy's excellent, but tough to follow analysis in PR 103226, this patch
fixes the bfin-elf regression.
In simplest terms the doloop patterns on this port may clobber the condition
code register, but they do not expose that until after register allocation.
That would be fine, except that other patterns have exposed CC earlier. As
a result the dataflow, particularly for CC, is incorrect.
This leads the register allocators to assume that a value in CC outside the
loop is still valid inside the loop when in fact, the value has been
clobbered. This is what caused pr80974 to start failing.
With this fix, not only do we fix the pr80974 regression, but we fix ~20
other execution failures in the port. It also reduces test time for the
port from ~90 minutes to ~60 minutes.
PR tree-optimization/103226
gcc/
* config/bfin/bfin.md (doloop pattern, splitter and expander):
Clobber
CC.
diff --git a/gcc/config/bfin/bfin.md b/gcc/config/bfin/bfin.md
index fd65f4d9e63..10a19aac23e 100644
--- a/gcc/config/bfin/bfin.md
+++ b/gcc/config/bfin/bfin.md
@@ -1959,7 +1959,8 @@
(plus:SI (match_dup 0)
(const_int -1)))
(unspec [(const_int 0)] UNSPEC_LSETUP_END)
- (clobber (match_dup 2))])] ; match_scratch
+ (clobber (match_dup 2))
+ (clobber (reg:BI REG_CC))])] ; match_scratch
""
{
/* The loop optimizer doesn't check the predicates... */
@@ -1979,7 +1980,8 @@
(plus (match_dup 2)
(const_int -1)))
(unspec [(const_int 0)] UNSPEC_LSETUP_END)
- (clobber (match_scratch:SI 3 "=X,&r,&r"))]
+ (clobber (match_scratch:SI 3 "=X,&r,&r"))
+ (clobber (reg:BI REG_CC))]
""
"@
/* loop end %0 %l1 */
@@ -1997,7 +1999,8 @@
(plus (match_dup 0)
(const_int -1)))
(unspec [(const_int 0)] UNSPEC_LSETUP_END)
- (clobber (match_scratch:SI 2))]
+ (clobber (match_scratch:SI 2))
+ (clobber (reg:BI REG_CC))]
"memory_operand (operands[0], SImode) || splitting_loops"
[(set (match_dup 2) (match_dup 0))
(set (match_dup 2) (plus:SI (match_dup 2) (const_int -1)))
