[PATCH] nvptx: Support floating point reciprocal instructions.

[Roger Sayle]

The following patch addds support for PTX's rcp.rn.f32 and rcp.rn.f64
instructions.  Note that the "rcp.rn" forms of this instruction
calculate the fully IEEE compliant result for the reciprocal, unlike
the rcp.approx variants that just provide fast approximations.

I'm undecided as to whether to prefix this instruction name with
"*" as this pattern is almost standard, so I can imagine the middle-end
potentially adding optab support for recip<mode>2 expansion at some
point.  I'll go with the (backend) reviewer's recommendation?

This patch has been tested on nvptx-none hosted on x86_64-pc-linux-gnu
with "make" and "make check" with no new regressions.
Ok for mainline?

2020-07-12  Roger Sayle  <ro...@nextmovesoftware.com>

gcc/ChangeLog
        * config/nvptx/nvptx.md (recip<mode>2): New instruction.

gcc/testsuite/ChangeLog
        * gcc.target/nvptx/recip-1.c: New test.


Thanks in advance,
Roger
--
Roger Sayle
NextMove Software
Cambridge, UK


diff --git a/gcc/config/nvptx/nvptx.md b/gcc/config/nvptx/nvptx.md
index 6545b81..ea6fc94 100644
--- a/gcc/config/nvptx/nvptx.md
+++ b/gcc/config/nvptx/nvptx.md
@@ -872,6 +872,15 @@
   ""
   "%.\\tfma%#%t0\\t%0, %1, %2, %3;")
 
+(define_insn "recip<mode>2"
+  [(set (match_operand:SDFM 0 "nvptx_register_operand" "=R")
+       (div:SDFM
+         (match_operand:SDFM 2 "const_double_operand" "F")
+         (match_operand:SDFM 1 "nvptx_register_operand" "R")))]
+  "CONST_DOUBLE_P (operands[2]) 
+   && real_identical (CONST_DOUBLE_REAL_VALUE (operands[2]), &dconst1)"
+  "%.\\trcp%#%t0\\t%0, %1;")
+
 (define_insn "div<mode>3"
   [(set (match_operand:SDFM 0 "nvptx_register_operand" "=R")
        (div:SDFM (match_operand:SDFM 1 "nvptx_register_operand" "R")
diff --git a/gcc/testsuite/gcc.target/nvptx/recip-1.c 
b/gcc/testsuite/gcc.target/nvptx/recip-1.c
new file mode 100644
index 0000000..9a165f1
--- /dev/null
+++ b/gcc/testsuite/gcc.target/nvptx/recip-1.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+double foo(double x)
+{
+  return 1.0/x;
+}
+
+float foof(float x)
+{
+  return 1.0f/x;
+}
+
+/* { dg-final { scan-assembler-times "rcp.rn.f64" 1 } } */
+/* { dg-final { scan-assembler-times "rcp.rn.f32" 1 } } */
+