Use a more efficient lowering of uint64_t --> float that can take advantage of hardware signed integer conversion without

having to do a double cast (uint64_t --> double --> float).  This is based on the algorithm from compiler_rt's __floatundisf
for X86-64.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@115634 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/X86/uint64-to-float.ll

@@ -0,0 +1,21 @@
+; RUN: llc < %s -march=x86-64 | FileCheck %s
+; Verify that we are using the efficient uitofp --> sitofp lowering illustrated
+; by the compiler_rt implementation of __floatundisf.
+; <rdar://problem/8493982>
+
+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"
+
+; CHECK: testq %rdi, %rdi
+; CHECK-NEXT: jns LBB0_2
+; CHECK: shrq
+; CHECK-NEXT: andq
+; CHECK-NEXT: orq
+; CHECK-NEXT: cvtsi2ss
+; CHECK: LBB0_2
+; CHECK-NEXT: cvtsi2ss
+define float @test(i64 %a) {
+entry:
+  %b = uitofp i64 %a to float
+  ret float %b
+}