add a note from PR6194

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95649 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/README-SSE.txt b/lib/Target/X86/README-SSE.txt
index a8f7f945b065046648faed44048d13445fc79dae..6e97ea6f9fc305d5766086374e07ed9fcb618376 100644 (file)
--- a/lib/Target/X86/README-SSE.txt
+++ b/lib/Target/X86/README-SSE.txt
@@ -954,3 +954,36 @@ 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 triple = "x86_64-apple-darwin10.0.0"
+
+%0 = type { double, double }
+%struct.float3 = type { float, float, float }
+
+define void @test(%0, %struct.float3* nocapture %res) nounwind noinline ssp {
+entry:
+  %tmp18 = extractvalue %0 %0, 0                  ; <double> [#uses=1]
+  %tmp19 = bitcast double %tmp18 to i64           ; <i64> [#uses=1]
+  %tmp20 = zext i64 %tmp19 to i128                ; <i128> [#uses=1]
+  %tmp10 = lshr i128 %tmp20, 32                   ; <i128> [#uses=1]
+  %tmp11 = trunc i128 %tmp10 to i32               ; <i32> [#uses=1]
+  %tmp12 = bitcast i32 %tmp11 to float            ; <float> [#uses=1]
+  %tmp5 = getelementptr inbounds %struct.float3* %res, i64 0, i32 1 ; <float*> [#uses=1]
+  store float %tmp12, float* %tmp5
+  ret void
+}
+
+Compiles to:
+
+_test:                                  ## @test
+       movd    %xmm0, %rax
+       shrq    $32, %rax
+       movl    %eax, 4(%rdi)
+       ret
+
+This would be better kept in the SSE unit by treating XMM0 as a 4xfloat and
+doing a shuffle from v[1] to v[0] then a float store.
+
+//===---------------------------------------------------------------------===//