LegalizeDAG: Fix and improve FCOPYSIGN/FABS legalization

- Factor out code to query and modify the sign bit of a floatingpoint
  value as an integer. This also works if none of the targets integer
  types is big enough to hold all bits of the floatingpoint value.

- Legalize FABS(x) as FCOPYSIGN(x, 0.0) if FCOPYSIGN is available,
  otherwise perform bit manipulation on the sign bit. The previous code
  used "x >u 0 ? x : -x" which is incorrect for x being -0.0! It also
  takes 34 instructions on ARM Cortex-M4. With this patch we only
  require 5:
    vldr d0, LCPI0_0
    vmov r2, r3, d0
    lsrs r2, r3, #31
    bfi r1, r2, #31, #1
    bx lr
  (This could be further improved if the compiler would recognize that
   r2, r3 is zero).

- Only lower FCOPYSIGN(x, y) = sign(x) ? -FABS(x) : FABS(x) if FABS is
  available otherwise perform bit manipulation on the sign bit.

- Perform the sign(x) test by masking out the sign bit and comparing
  with 0 rather than shifting the sign bit to the highest position and
  testing for "<s 0". For x86 copysignl (on 80bit values) this gets us:
    testl $32768, %eax
  rather than:
    shlq $48, %rax
    sets %al
    testb %al, %al

llvm-svn: 242107

2 files changed, 7 insertions, 6 deletions

diff --git a/llvm/test/CodeGen/Thumb2/float-intrinsics-double.ll b/llvm/test/CodeGen/Thumb2/float-intrinsics-double.ll
index 01a23bd0fe6..b34176d41a4 100644
--- a/llvm/test/CodeGen/Thumb2/float-intrinsics-double.ll
+++ b/llvm/test/CodeGen/Thumb2/float-intrinsics-double.ll
@@ -109,9 +109,12 @@ declare double     @llvm.fabs.f64(double %Val)
 define double @abs_d(double %a) {
 ; CHECK-LABEL: abs_d:
 ; NONE: bic r1, r1, #-2147483648
-; SP: bl __aeabi_dcmpgt
-; SP: bl __aeabi_dcmpun
-; SP: bl __aeabi_dsub
+; SP: vldr d1, .LCPI{{.*}}
+; SP: vmov r0, r1, d0
+; SP: vmov r2, r3, d1
+; SP: lsrs r2, r3, #31
+; SP: bfi r1, r2, #31, #1
+; SP: vmov d0, r0, r1
 ; DP: vabs.f64 d0, d0
   %1 = call double @llvm.fabs.f64(double %a)
   ret double %1
diff --git a/llvm/test/CodeGen/X86/pr13577.ll b/llvm/test/CodeGen/X86/pr13577.ll
index 090c7262d6e..13b3665d1a7 100644
--- a/llvm/test/CodeGen/X86/pr13577.ll
+++ b/llvm/test/CodeGen/X86/pr13577.ll
@@ -7,9 +7,7 @@
 
 ; CHECK-LABEL: foo:
 ; CHECK: movq {{.*}}, %rax
-; CHECK: shlq $48, %rax
-; CHECK: sets %al
-; CHECK: testb %al, %al
+; CHECK: testl $32768, %eax
 ; CHECK: flds LCPI0_0(%rip)
 ; CHECK: flds LCPI0_1(%rip)
 ; CHECK: fcmovne %st(1), %st(0)