This patch to the nvptx backend changes the backend's STORE_FLAG_VALUE
from -1 to 1, by using BImode predicates and selp instructions, instead
of set instructions (almost always followed by integer negation).
Historically, it was reasonable (through rare) for backends to use -1
for representing true during the RTL passes. However with tree-ssa,
GCC now emits lots of code that reads and writes _Bool values, requiring
STORE_FLAG_VALUE=-1 targets to frequently convert 0/-1 pseudos to 0/1
pseudos using integer negation. Unfortunately, this process prevents
or complicates many optimizations (negate isn't associative with logical
AND, OR and XOR, and interferes with range/vrp/nonzerobits bounds etc.).
The impact of this is that for a relatively simple logical expression
like "return (x==21) && (y==69);", the nvptx backend currently generates:
mov.u32 %r26, %ar0;
mov.u32 %r27, %ar1;
set.u32.eq.u32 %r30, %r26, 21;
neg.s32 %r31, %r30;
mov.u32 %r29, %r31;
set.u32.eq.u32 %r33, %r27, 69;
neg.s32 %r34, %r33;
mov.u32 %r32, %r34;
cvt.u16.u8 %r39, %r29;
mov.u16 %r36, %r39;
cvt.u16.u8 %r39, %r32;
mov.u16 %r37, %r39;
and.b16 %r35, %r36, %r37;
cvt.u32.u16 %r38, %r35;
cvt.u32.u8 %value, %r38;
This patch tweaks nvptx to generate 0/1 values instead, requiring the
same number of instructions, using (BImode) predicate registers and selp
instructions so as to now generate the almost identical:
mov.u32 %r26, %ar0;
mov.u32 %r27, %ar1;
setp.eq.u32 %r31, %r26, 21;
selp.u32%r30, 1, 0, %r31;
mov.u32 %r29, %r30;
setp.eq.u32 %r34, %r27, 69;
selp.u32%r33, 1, 0, %r34;
mov.u32 %r32, %r33;
cvt.u16.u8 %r39, %r29;
mov.u16 %r36, %r39;
cvt.u16.u8 %r39, %r32;
mov.u16 %r37, %r39;
and.b16 %r35, %r36, %r37;
cvt.u32.u16 %r38, %r35;
cvt.u32.u8 %value, %r38;
The hidden benefit is that this sequence can (in theory) be optimized
by the RTL passes to eventually generate a much shorter sequence using
an and.pred instruction (just like Nvidia's nvcc compiler).
This patch has been tested nvptx-none with a "make" and "make -k check"
(including newlib) hosted on x86_64-pc-linux-gnu with no new failures.
Ok for mainline?
2021-10-05 Roger Sayle
gcc/ChangeLog
* config/nvptx/nvptx.h (STORE_FLAG_VALUE): Change to 1.
* config/nvptx/nvptx.md (movbi): Use P1 constraint for true.
(setcc_from_bi): Remove SImode specific pattern.
(setcc_from_bi): Provide more general HSDIM pattern.
(extendbi2, zeroextendbi2): Provide instructions
for sign- and zero-extending BImode predicates to integers.
(setcc_int): Remove previous (-1-based) instructions.
(cstorebi4): Remove BImode to SImode specific expander.
(cstore4): Fix indentation. Expand using setccsi_from_bi.
(cstore4): For both integer and floating point modes.
Thanks in advance,
Roger
--
diff --git a/gcc/config/nvptx/nvptx.h b/gcc/config/nvptx/nvptx.h
index d367174..fcebcf9 100644
--- a/gcc/config/nvptx/nvptx.h
+++ b/gcc/config/nvptx/nvptx.h
@@ -315,7 +315,7 @@ struct GTY(()) machine_function
#define NO_DOT_IN_LABEL
#define ASM_COMMENT_START "//"
-#define STORE_FLAG_VALUE -1
+#define STORE_FLAG_VALUE 1
#define FLOAT_STORE_FLAG_VALUE(MODE) REAL_VALUE_ATOF("1.0", (MODE))
#define CASE_VECTOR_MODE SImode
diff --git a/gcc/config/nvptx/nvptx.md b/gcc/config/nvptx/nvptx.md
index 108de1c..b3275b1 100644
--- a/gcc/config/nvptx/nvptx.md
+++ b/gcc/config/nvptx/nvptx.md
@@ -213,7 +213,7 @@
;; get variables in this mode and pseudos are never spilled.
(define_insn "movbi"
[(set (match_operand:BI 0 "nvptx_register_operand" "=R,R,R")
- (match_operand:BI 1 "nvptx_nonmemory_operand" "R,P0,Pn"))]
+ (match_operand:BI 1 "nvptx_nonmemory_operand" "R,P0,P1"))]
""
"@
%.\\tmov%t0\\t%0, %1;
@@ -789,12 +789,26 @@
;; Conditional stores
-(define_insn "setcc_from_bi"
- [(set (match_operand:SI 0 "nvptx_register_operand" "=R")
- (ne:SI (match_operand:BI 1 "nvptx_register_operand" "R")
- (const_int 0)))]
+(define_insn "setcc_from_bi"
+ [(set (match_operand:HSDIM 0 "nvptx_register_operand" "=R")
+ (ne:HSDIM (match_operand:BI 1 "nvptx_register_operand" "R")
+ (const_int 0)))]
+ ""
+ "%.\\tselp%t0\\t%0, 1, 0, %1;")
+
+(define_insn "extendbi2"
+ [(set (match_operand:HSDIM 0 "nvptx_register_operand" "=R")
+ (sign_extend:HSDIM
+(match_operand:BI 1 "nvptx_register_operand" "R")))]
+ ""
+ "%.\\tselp%t0\\t%0, -1, 0, %1;")
+
+(define_i
