[X86] Teach FCOPYSIGN lowering to recognize constant magnitudes.

For code like:
    float foo(float x) { return copysign(1.0, x); }
We used to generate:
    andps  <-0.000000e+00,0,0,0>, %xmm0
    movss  <1.000000e+00>, %xmm1
    andps  <nan>, %xmm1
    orps   %xmm0, %xmm1
Basically doing an abs(1.0f) in the two middle instructions.

We now generate:
    andps  <-0.000000e+00,0,0,0>, %xmm0
    orps   <1.000000e+00,0,0,0>, %xmm0

Builds on cleanups r223415, r223542.
rdar://19049548
Differential Revision: http://reviews.llvm.org/D6555

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225357 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 98935890d367f8dd340374bed1bbb119b1efb772..57fedb8f387a8207415ca6bb072f0f97acb9e0ec 100644 (file)
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -14530,14 +14530,27 @@ static SDValue LowerFCOPYSIGN(SDValue Op, SelectionDAG &DAG) {
   SDValue SignBit = DAG.getNode(X86ISD::FAND, dl, SrcVT, Op1, Mask1);
 
   // Next, clear the sign bit from the first operand (magnitude).
-  CV[0] = ConstantFP::get(
-      *Context, APFloat(Sem, APInt::getLowBitsSet(SizeInBits, SizeInBits - 1)));
+  // If it's a constant, we can clear it here.
+  if (ConstantFPSDNode *Op0CN = dyn_cast<ConstantFPSDNode>(Op0)) {
+    APFloat APF = Op0CN->getValueAPF();
+    // If the magnitude is a positive zero, the sign bit alone is enough.
+    if (APF.isPosZero())
+      return SignBit;
+    APF.clearSign();
+    CV[0] = ConstantFP::get(*Context, APF);
+  } else {
+    CV[0] = ConstantFP::get(
+        *Context,
+        APFloat(Sem, APInt::getLowBitsSet(SizeInBits, SizeInBits - 1)));
+  }
   C = ConstantVector::get(CV);
   CPIdx = DAG.getConstantPool(C, TLI.getPointerTy(), 16);
-  SDValue Mask2 = DAG.getLoad(VT, dl, DAG.getEntryNode(), CPIdx,
-                              MachinePointerInfo::getConstantPool(),
-                              false, false, false, 16);
-  SDValue Val = DAG.getNode(X86ISD::FAND, dl, VT, Op0, Mask2);
+  SDValue Val = DAG.getLoad(VT, dl, DAG.getEntryNode(), CPIdx,
+                            MachinePointerInfo::getConstantPool(),
+                            false, false, false, 16);
+  // If the magnitude operand wasn't a constant, we need to AND out the sign.
+  if (!isa<ConstantFPSDNode>(Op0))
+    Val = DAG.getNode(X86ISD::FAND, dl, VT, Op0, Val);
 
   // OR the magnitude value with the sign bit.
   return DAG.getNode(X86ISD::FOR, dl, VT, Val, SignBit);

diff --git a/test/CodeGen/X86/copysign-constant-magnitude.ll b/test/CodeGen/X86/copysign-constant-magnitude.ll
new file mode 100644 (file)
index 0000000..537d629
--- /dev/null
+++ b/test/CodeGen/X86/copysign-constant-magnitude.ll
@@ -0,0 +1,105 @@
+; RUN: llc < %s | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.10.0"
+
+define void @test_copysign_const_magnitude_d(double %X) {
+; CHECK: [[SIGNMASK:L.+]]:
+; CHECK-NEXT:   .quad -9223372036854775808    ## double -0.000000e+00
+; CHECK-NEXT:   .quad 0                       ## double 0.000000e+00
+; CHECK: [[ZERO:L.+]]:
+; CHECK-NEXT:   .space 16
+; CHECK: [[ONE:L.+]]:
+; CHECK-NEXT:   .quad 4607182418800017408     ## double 1.000000e+00
+; CHECK-NEXT:   .quad 0                       ## double 0.000000e+00
+; CHECK-LABEL: test_copysign_const_magnitude_d:
+
+; CHECK: id
+  %iX = call double @id_d(double %X)
+
+; CHECK-NEXT: andpd [[SIGNMASK]](%rip), %xmm0
+  %d0 = call double @copysign(double 0.000000e+00, double %iX)
+
+; CHECK-NEXT: id
+  %id0 = call double @id_d(double %d0)
+
+; CHECK-NEXT: andpd [[SIGNMASK]](%rip), %xmm0
+; CHECK-NEXT: orpd [[ZERO]](%rip), %xmm0
+  %dn0 = call double @copysign(double -0.000000e+00, double %id0)
+
+; CHECK-NEXT: id
+  %idn0 = call double @id_d(double %dn0)
+
+; CHECK-NEXT: andpd [[SIGNMASK]](%rip), %xmm0
+; CHECK-NEXT: orpd [[ONE]](%rip), %xmm0
+  %d1 = call double @copysign(double 1.000000e+00, double %idn0)
+
+; CHECK-NEXT: id
+  %id1 = call double @id_d(double %d1)
+
+; CHECK-NEXT: andpd [[SIGNMASK]](%rip), %xmm0
+; CHECK-NEXT: orpd [[ONE]](%rip), %xmm0
+  %dn1 = call double @copysign(double -1.000000e+00, double %id1)
+
+; CHECK-NEXT: id
+  %idn1 = call double @id_d(double %dn1)
+
+; CHECK: retq
+  ret void
+}
+
+define void @test_copysign_const_magnitude_f(float %X) {
+; CHECK: [[SIGNMASK:L.+]]:
+; CHECK-NEXT:   .long  2147483648              ## float -0.000000e+00
+; CHECK-NEXT:   .long  0                       ## float 0.000000e+00
+; CHECK-NEXT:   .long  0                       ## float 0.000000e+00
+; CHECK-NEXT:   .long  0                       ## float 0.000000e+00
+; CHECK: [[ZERO:L.+]]:
+; CHECK-NEXT:   .space 16
+; CHECK: [[ONE:L.+]]:
+; CHECK-NEXT:   .long  1065353216              ## float 1.000000e+00
+; CHECK-NEXT:   .long  0                       ## float 0.000000e+00
+; CHECK-NEXT:   .long  0                       ## float 0.000000e+00
+; CHECK-NEXT:   .long  0                       ## float 0.000000e+00
+; CHECK-LABEL: test_copysign_const_magnitude_f:
+
+; CHECK: id
+  %iX = call float @id_f(float %X)
+
+; CHECK-NEXT: andps [[SIGNMASK]](%rip), %xmm0
+  %d0 = call float @copysignf(float 0.000000e+00, float %iX)
+
+; CHECK-NEXT: id
+  %id0 = call float @id_f(float %d0)
+
+; CHECK-NEXT: andps [[SIGNMASK]](%rip), %xmm0
+; CHECK-NEXT: orps [[ZERO]](%rip), %xmm0
+  %dn0 = call float @copysignf(float -0.000000e+00, float %id0)
+
+; CHECK-NEXT: id
+  %idn0 = call float @id_f(float %dn0)
+
+; CHECK-NEXT: andps [[SIGNMASK]](%rip), %xmm0
+; CHECK-NEXT: orps [[ONE]](%rip), %xmm0
+  %d1 = call float @copysignf(float 1.000000e+00, float %idn0)
+
+; CHECK-NEXT: id
+  %id1 = call float @id_f(float %d1)
+
+; CHECK-NEXT: andps [[SIGNMASK]](%rip), %xmm0
+; CHECK-NEXT: orps [[ONE]](%rip), %xmm0
+  %dn1 = call float @copysignf(float -1.000000e+00, float %id1)
+
+; CHECK-NEXT: id
+  %idn1 = call float @id_f(float %dn1)
+
+; CHECK: retq
+  ret void
+}
+
+declare double @copysign(double, double) nounwind readnone
+declare float @copysignf(float, float) nounwind readnone
+
+; Dummy identity functions, so we always have xmm0, and prevent optimizations.
+declare double @id_d(double)
+declare float @id_f(float)

diff --git a/test/CodeGen/X86/copysign-zero.ll b/test/CodeGen/X86/copysign-zero.ll
deleted file mode 100644 (file)
index 47522d8..0000000
--- a/test/CodeGen/X86/copysign-zero.ll
+++ /dev/null
@@ -1,14 +0,0 @@
-; RUN: llc < %s | not grep orpd
-; RUN: llc < %s | grep andpd | count 1
-
-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"
-target triple = "x86_64-apple-darwin8"
-
-define double @test(double %X) nounwind  {
-entry:
-       %tmp2 = tail call double @copysign( double 0.000000e+00, double %X ) nounwind readnone          ; <double> [#uses=1]
-       ret double %tmp2
-}
-
-declare double @copysign(double, double) nounwind readnone 
-