This patch addresses the "increased register pressure" regression on
nvptx-none caused by my change to transition the backend to a
STORE_FLAG_VALUE = 1 target. This improved code generation for the
more common case of producing 0/1 Boolean values, but unfortunately
made things marginally worse when a 0/-1 mask value is desired.
Unfortunately, nvptx kernels are extremely sensitive to changes in
register usage, which was observable in the reported PR.
This patch provides optimizations for -(cond ? 1 : 0), effectively
simplify this into cond ? -1 : 0, where these ternary operators are
provided by nvptx's selp instruction, and for the specific case of
SImode, using (restoring) nvptx's "set" instruction (which avoids
the need for a predicate register).
This patch has been tested on nvptx-none hosted on x86_64-pc-linux-gnu
with a "make" and "make -k check" with no new failures. Unfortunately,
the exact register usage of a nvptx kernel depends upon the version of
the Cuda drivers being used (and the hardware), but I believe this
change should resolve the PR (for Thomas) by improving code generation
for the cases that regressed. Ok for mainline?
2022-02-03 Roger Sayle <ro...@nextmovesoftware.com>
gcc/ChangeLog
PR target/104345
* config/nvptx/nvptx.md (sel_true<mode>): Fix indentation.
(sel_false<mode>): Likewise.
(define_code_iterator eqne): New code iterator for EQ and NE.
(*selp<mode>_neg_<code>): New define_insn_and_split to optimize
the negation of a selp instruction.
(*selp<mode>_not_<code>): New define_insn_and_split to optimize
the bitwise not of a selp instruction.
(*setcc_int<mode>): Use set instruction for neg:SI of a selp.
gcc/testsuite/ChangeLog
PR target/104345
* gcc.target/nvptx/neg-selp.c: New test case.
Thanks in advance,
Roger
--
diff --git a/gcc/config/nvptx/nvptx.md b/gcc/config/nvptx/nvptx.md
index 92768dd..651ba20 100644
--- a/gcc/config/nvptx/nvptx.md
+++ b/gcc/config/nvptx/nvptx.md
@@ -892,7 +892,7 @@
(define_insn "sel_true<mode>"
[(set (match_operand:HSDIM 0 "nvptx_register_operand" "=R")
- (if_then_else:HSDIM
+ (if_then_else:HSDIM
(ne (match_operand:BI 1 "nvptx_register_operand" "R") (const_int 0))
(match_operand:HSDIM 2 "nvptx_nonmemory_operand" "Ri")
(match_operand:HSDIM 3 "nvptx_nonmemory_operand" "Ri")))]
@@ -901,7 +901,7 @@
(define_insn "sel_true<mode>"
[(set (match_operand:SDFM 0 "nvptx_register_operand" "=R")
- (if_then_else:SDFM
+ (if_then_else:SDFM
(ne (match_operand:BI 1 "nvptx_register_operand" "R") (const_int 0))
(match_operand:SDFM 2 "nvptx_nonmemory_operand" "RF")
(match_operand:SDFM 3 "nvptx_nonmemory_operand" "RF")))]
@@ -910,7 +910,7 @@
(define_insn "sel_false<mode>"
[(set (match_operand:HSDIM 0 "nvptx_register_operand" "=R")
- (if_then_else:HSDIM
+ (if_then_else:HSDIM
(eq (match_operand:BI 1 "nvptx_register_operand" "R") (const_int 0))
(match_operand:HSDIM 2 "nvptx_nonmemory_operand" "Ri")
(match_operand:HSDIM 3 "nvptx_nonmemory_operand" "Ri")))]
@@ -919,13 +919,63 @@
(define_insn "sel_false<mode>"
[(set (match_operand:SDFM 0 "nvptx_register_operand" "=R")
- (if_then_else:SDFM
+ (if_then_else:SDFM
(eq (match_operand:BI 1 "nvptx_register_operand" "R") (const_int 0))
(match_operand:SDFM 2 "nvptx_nonmemory_operand" "RF")
(match_operand:SDFM 3 "nvptx_nonmemory_operand" "RF")))]
""
"%.\\tselp%t0\\t%0, %3, %2, %1;")
+(define_code_iterator eqne [eq ne])
+
+;; Split negation of a predicate into a conditional move.
+(define_insn_and_split "*selp<mode>_neg_<code>"
+ [(set (match_operand:HSDIM 0 "nvptx_register_operand" "=R")
+ (neg:HSDIM (eqne:HSDIM
+ (match_operand:BI 1 "nvptx_register_operand" "R")
+ (const_int 0))))]
+ ""
+ "#"
+ "&& 1"
+ [(set (match_dup 0)
+ (if_then_else:HSDIM
+ (eqne (match_dup 1) (const_int 0))
+ (const_int -1)
+ (const_int 0)))])
+
+;; Split bitwise not of a predicate into a conditional move.
+(define_insn_and_split "*selp<mode>_not_<code>"
+ [(set (match_operand:HSDIM 0 "nvptx_register_operand" "=R")
+ (not:HSDIM (eqne:HSDIM
+ (match_operand:BI 1 "nvptx_register_operand" "R")
+ (const_int 0))))]
+ ""
+ "#"
+ "&& 1"
+ [(set (match_dup 0)
+ (if_then_else:HSDIM
+ (eqne (match_dup 1) (const_int 0))
+ (const_int -2)
+ (const_int -1)))])
+
+(define_insn "*setcc_int<mode>"
+ [(set (match_operand:SI 0 "nvptx_register_operand" "=R")
+ (neg:SI
+ (match_operator:SI 1 "nvptx_comparison_operator"
+ [(match_operand:HSDIM 2 "nvptx_register_operand" "R")
+ (match_operand:HSDIM 3 "nvptx_nonmemory_operand" "Ri")])))]
+ ""
+ "%.\\tset%t0%c1\\t%0, %2, %3;")
+
+(define_insn "*setcc_int<mode>"
+ [(set (match_operand:SI 0 "nvptx_register_operand" "=R")
+ (neg:SI
+ (match_operator:SI 1 "nvptx_float_comparison_operator"
+ [(match_operand:SDFM 2 "nvptx_register_operand" "R")
+ (match_operand:SDFM 3 "nvptx_nonmemory_operand" "RF")])))]
+ ""
+ "%.\\tset%t0%c1\\t%0, %2, %3;")
+
(define_insn "setcc_float<mode>"
[(set (match_operand:SF 0 "nvptx_register_operand" "=R")
(match_operator:SF 1 "nvptx_comparison_operator"
diff --git a/gcc/testsuite/gcc.target/nvptx/neg-selp.c
b/gcc/testsuite/gcc.target/nvptx/neg-selp.c
new file mode 100644
index 0000000..a8f0118
--- /dev/null
+++ b/gcc/testsuite/gcc.target/nvptx/neg-selp.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+int neg(int x, int y)
+{
+ int t = (x == y) ? 1 : 0;
+ return -t;
+}
+
+int not(int x, int y)
+{
+ int t = (x == y) ? 1 : 0;
+ return ~t;
+}
+
+/* { dg-final { scan-assembler-not "neg.s32" } } */
+/* { dg-final { scan-assembler-not "not.b32" } } */
