Support v8f32 to v8i8/vi816 conversion through custom lowering

[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 b2116e03b148ea222532c956e9dd78f49fea3a06..40110353fc6237ade72586ab2f1e3e2ed8f507c7 100644 (file)
--- a/lib/Target/X86/README-SSE.txt
+++ b/lib/Target/X86/README-SSE.txt
@@ -862,7 +862,7 @@ define float @bar(float %x) nounwind {
 
 This IR (from PR6194):
 
-target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 target triple = "x86_64-apple-darwin10.0.0"
 
 %0 = type { double, double }
@@ -923,4 +923,33 @@ The insertps's of $0 are pointless complex copies.
 
 //===---------------------------------------------------------------------===//
 
+[UNSAFE FP]
 
+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:
+
+#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.
+
+//===---------------------------------------------------------------------===//