[llvm] e4aa6ad - [X86][SSE] X86ISD::FSETCC nodes (cmpss/cmpsd) return a 0/-1 allbits signbits result

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2021-07-12T09:56:59+01:00
New Revision: e4aa6ad132164839a4a97dff0d433ea4766f77f1

URL: https://github.com/llvm/llvm-project/commit/e4aa6ad132164839a4a97dff0d433ea4766f77f1
DIFF: https://github.com/llvm/llvm-project/commit/e4aa6ad132164839a4a97dff0d433ea4766f77f1.diff

LOG: [X86][SSE] X86ISD::FSETCC nodes (cmpss/cmpsd) return a 0/-1 allbits signbits result

Annoyingly, i686 cmpsd handling still fails to remove the unnecessary neg(and(x,1))

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86ISelLowering.cpp
    llvm/test/CodeGen/X86/known-signbits-vector.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 0410a6923310c..f5c61b8689ba1 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -34922,6 +34922,11 @@ unsigned X86TargetLowering::ComputeNumSignBitsForTargetNode(
     return ShiftVal.uge(VTBits) ? VTBits : ShiftVal.getZExtValue();
   }
 
+  case X86ISD::FSETCC:
+    // Scalar cmpss/cmpsd return zero/all-bits result values.
+    assert((VT == MVT::f32 || VT == MVT::f64) && "Unexpected fp scalar result");
+    return VTBits;
+
   case X86ISD::PCMPGT:
   case X86ISD::PCMPEQ:
   case X86ISD::CMPP:

diff  --git a/llvm/test/CodeGen/X86/known-signbits-vector.ll b/llvm/test/CodeGen/X86/known-signbits-vector.ll
index ff5c62d9e7b48..9b31dca38696d 100644
--- a/llvm/test/CodeGen/X86/known-signbits-vector.ll
+++ b/llvm/test/CodeGen/X86/known-signbits-vector.ll
@@ -666,22 +666,19 @@ define i32 @signbits_cmpss(float %0, float %1) {
 ; X86-NEXT:    vmovss {{.*#+}} xmm0 = mem[0],zero,zero,zero
 ; X86-NEXT:    vcmpeqss {{[0-9]+}}(%esp), %xmm0, %xmm0
 ; X86-NEXT:    vmovd %xmm0, %eax
-; X86-NEXT:    andl $1, %eax
-; X86-NEXT:    negl %eax
 ; X86-NEXT:    retl
 ;
 ; X64-LABEL: signbits_cmpss:
 ; X64:       # %bb.0:
 ; X64-NEXT:    vcmpeqss %xmm1, %xmm0, %xmm0
 ; X64-NEXT:    vmovd %xmm0, %eax
-; X64-NEXT:    andl $1, %eax
-; X64-NEXT:    negl %eax
 ; X64-NEXT:    retq
   %3 = fcmp oeq float %0, %1
   %4 = sext i1 %3 to i32
   ret i32 %4
 }
 
+; FIXME: X86 fails to remove the unnecessary neg(and(x,1))
 define i64 @signbits_cmpsd(double %0, double %1) {
 ; X86-LABEL: signbits_cmpsd:
 ; X86:       # %bb.0:
@@ -697,8 +694,6 @@ define i64 @signbits_cmpsd(double %0, double %1) {
 ; X64:       # %bb.0:
 ; X64-NEXT:    vcmpeqsd %xmm1, %xmm0, %xmm0
 ; X64-NEXT:    vmovq %xmm0, %rax
-; X64-NEXT:    andl $1, %eax
-; X64-NEXT:    negq %rax
 ; X64-NEXT:    retq
   %3 = fcmp oeq double %0, %1
   %4 = sext i1 %3 to i64