Added encoding prefixes for KNL instructions (EVEX).

[oota-llvm.git] / lib / Target / X86 / README-SSE.txt

diff --git a/lib/Target/X86/README-SSE.txt b/lib/Target/X86/README-SSE.txt
index 7d901afae47499b401dc409f664922e6fc1da4ca..496b704ee85fb16878eb8585a77121b78497a674 100644 (file)
--- a/lib/Target/X86/README-SSE.txt
+++ b/lib/Target/X86/README-SSE.txt
@@ -923,15 +923,42 @@ The insertps's of $0 are pointless complex copies.
 
 //===---------------------------------------------------------------------===//
 
-If SSE4.1 is available we should inline rounding functions instead of emitting
-a libcall.
+[UNSAFE FP]
 
-floor: roundsd $0x01, %xmm, %xmm
-ceil:  roundsd $0x02, %xmm, %xmm
+void foo(double, double, double);
+void norm(double x, double y, double z) {
+  double scale = __builtin_sqrt(x*x + y*y + z*z);
+  foo(x/scale, y/scale, z/scale);
+}
+
+We currently generate an sqrtsd and 3 divsd instructions. This is bad, fp div is
+slow and not pipelined. In -ffast-math mode we could compute "1.0/scale" first
+and emit 3 mulsd in place of the divs. This can be done as a target-independent
+transform.
+
+If we're dealing with floats instead of doubles we could even replace the sqrtss
+and inversion with an rsqrtss instruction, which computes 1/sqrt faster at the
+cost of reduced accuracy.
+
+//===---------------------------------------------------------------------===//
+
+This function should be matched to haddpd when the appropriate CPU is enabled:
 
-and likewise for the single precision versions.
+#include <x86intrin.h>
+double f (__m128d p) {
+  return p[0] + p[1];
+}
+
+similarly, v[0]-v[1] should match to hsubpd, and {v[0]-v[1], w[0]-w[1]} should
+turn into hsubpd also.
+
+//===---------------------------------------------------------------------===//
+
+define <2 x i32> @foo(<2 x double> %in) {
+  %x = fptosi <2 x double> %in to <2 x i32>
+  ret <2 x i32> %x
+}
 
-Currently, SelectionDAGBuilder doesn't turn calls to these functions into the
-corresponding nodes and some targets (including X86) aren't ready for them.
+Should compile into cvttpd2dq instead of being scalarized into 2 cvttsd2si.
 
 //===---------------------------------------------------------------------===//