[X86] Disable a DAG combine to allow packed AVX512DQ instructions to be consistently used for i64->float/double conversions.

[craig.topper]

Summary

We already get this right if the i64 didn't come from a load.

[RKSimon]

LGTM

lib/Target/X86/X86ISelLowering.cpp

   if (!Subtarget.useSoftFloat() && Op0.getOpcode() == ISD::LOAD) {
     LoadSDNode *Ld = cast<LoadSDNode>(Op0.getNode());
     EVT LdVT = Ld->getValueType(0);
 
     // This transformation is not supported if the result type is f16 or f128.
     if (VT == MVT::f16 || VT == MVT::f128)
       return SDValue();
 
+    // If we have AVX512DQ we can use packed conversion instructions unless
+    // the VT is f80.
+    if (Subtarget.hasDQI() && VT != MVT::f80)
+      return SDValue();
+
     if (!Ld->isVolatile() && !VT.isVector() &&
         ISD::isNON_EXTLoad(Op0.getNode()) && Op0.hasOneUse() &&
         !Subtarget.is64Bit() && LdVT == MVT::i64) {
       SDValue FILDChain = Subtarget.getTargetLowering()->BuildFILD(
           SDValue(N, 0), LdVT, Ld->getChain(), Op0, DAG);
       DAG.ReplaceAllUsesOfValueWith(Op0.getValue(1), FILDChain.getValue(1));
       return FILDChain;
     }

test/CodeGen/X86/scalar-int-to-fp.ll

 ; X87-NEXT:    movl %ebp, %esp
 ; X87-NEXT:    popl %ebp
 ; X87-NEXT:    retl
   %r = uitofp i64 %a to float
   ret float %r
 }
 
 define float @s64_to_f(i64 %a) nounwind {
-; AVX512_32-LABEL: s64_to_f:
-; AVX512_32:       # %bb.0:
-; AVX512_32-NEXT:    pushl %eax
-; AVX512_32-NEXT:    fildll {{[0-9]+}}(%esp)
-; AVX512_32-NEXT:    fstps (%esp)
-; AVX512_32-NEXT:    flds (%esp)
-; AVX512_32-NEXT:    popl %eax
-; AVX512_32-NEXT:    retl
+; AVX512DQVL_32-LABEL: s64_to_f:
+; AVX512DQVL_32:       # %bb.0:
+; AVX512DQVL_32-NEXT:    pushl %eax
+; AVX512DQVL_32-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
+; AVX512DQVL_32-NEXT:    vcvtqq2ps %ymm0, %xmm0
+; AVX512DQVL_32-NEXT:    vmovss %xmm0, (%esp)
+; AVX512DQVL_32-NEXT:    flds (%esp)
+; AVX512DQVL_32-NEXT:    popl %eax
+; AVX512DQVL_32-NEXT:    vzeroupper
+; AVX512DQVL_32-NEXT:    retl
 ;
 ; AVX512_64-LABEL: s64_to_f:
 ; AVX512_64:       # %bb.0:
 ; AVX512_64-NEXT:    vcvtsi2ssq %rdi, %xmm0, %xmm0
 ; AVX512_64-NEXT:    retq
 ;
+; AVX512DQ_32-LABEL: s64_to_f:
+; AVX512DQ_32:       # %bb.0:
+; AVX512DQ_32-NEXT:    pushl %eax
+; AVX512DQ_32-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
+; AVX512DQ_32-NEXT:    vcvtqq2ps %zmm0, %ymm0
+; AVX512DQ_32-NEXT:    vmovss %xmm0, (%esp)
+; AVX512DQ_32-NEXT:    flds (%esp)
+; AVX512DQ_32-NEXT:    popl %eax
+; AVX512DQ_32-NEXT:    vzeroupper
+; AVX512DQ_32-NEXT:    retl
+;
+; AVX512F_32-LABEL: s64_to_f:
+; AVX512F_32:       # %bb.0:
+; AVX512F_32-NEXT:    pushl %eax
+; AVX512F_32-NEXT:    fildll {{[0-9]+}}(%esp)
+; AVX512F_32-NEXT:    fstps (%esp)
+; AVX512F_32-NEXT:    flds (%esp)
+; AVX512F_32-NEXT:    popl %eax
+; AVX512F_32-NEXT:    retl
+;
 ; SSE2_32-LABEL: s64_to_f:
 ; SSE2_32:       # %bb.0:
 ; SSE2_32-NEXT:    pushl %eax
 ; SSE2_32-NEXT:    fildll {{[0-9]+}}(%esp)
 ; SSE2_32-NEXT:    fstps (%esp)
 ; SSE2_32-NEXT:    flds (%esp)
 ; SSE2_32-NEXT:    popl %eax
 ; SSE2_32-NEXT:    retl

 ; X87-NEXT:    movl %ebp, %esp
 ; X87-NEXT:    popl %ebp
 ; X87-NEXT:    retl
   %r = uitofp i64 %a to double
   ret double %r
 }
 
 define double @s64_to_d(i64 %a) nounwind {
-; AVX512_32-LABEL: s64_to_d:
-; AVX512_32:       # %bb.0:
-; AVX512_32-NEXT:    pushl %ebp
-; AVX512_32-NEXT:    movl %esp, %ebp
-; AVX512_32-NEXT:    andl $-8, %esp
-; AVX512_32-NEXT:    subl $8, %esp
-; AVX512_32-NEXT:    fildll 8(%ebp)
-; AVX512_32-NEXT:    fstpl (%esp)
-; AVX512_32-NEXT:    fldl (%esp)
-; AVX512_32-NEXT:    movl %ebp, %esp
-; AVX512_32-NEXT:    popl %ebp
-; AVX512_32-NEXT:    retl
+; AVX512DQVL_32-LABEL: s64_to_d:
+; AVX512DQVL_32:       # %bb.0:
+; AVX512DQVL_32-NEXT:    pushl %ebp
+; AVX512DQVL_32-NEXT:    movl %esp, %ebp
+; AVX512DQVL_32-NEXT:    andl $-8, %esp
+; AVX512DQVL_32-NEXT:    subl $8, %esp
+; AVX512DQVL_32-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
+; AVX512DQVL_32-NEXT:    vcvtqq2pd %ymm0, %ymm0
+; AVX512DQVL_32-NEXT:    vmovlps %xmm0, (%esp)
+; AVX512DQVL_32-NEXT:    fldl (%esp)
+; AVX512DQVL_32-NEXT:    movl %ebp, %esp
+; AVX512DQVL_32-NEXT:    popl %ebp
+; AVX512DQVL_32-NEXT:    vzeroupper
+; AVX512DQVL_32-NEXT:    retl
 ;
 ; AVX512_64-LABEL: s64_to_d:
 ; AVX512_64:       # %bb.0:
 ; AVX512_64-NEXT:    vcvtsi2sdq %rdi, %xmm0, %xmm0
 ; AVX512_64-NEXT:    retq
 ;
+; AVX512DQ_32-LABEL: s64_to_d:
+; AVX512DQ_32:       # %bb.0:
+; AVX512DQ_32-NEXT:    pushl %ebp
+; AVX512DQ_32-NEXT:    movl %esp, %ebp
+; AVX512DQ_32-NEXT:    andl $-8, %esp
+; AVX512DQ_32-NEXT:    subl $8, %esp
+; AVX512DQ_32-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
+; AVX512DQ_32-NEXT:    vcvtqq2pd %zmm0, %zmm0
+; AVX512DQ_32-NEXT:    vmovlps %xmm0, (%esp)
+; AVX512DQ_32-NEXT:    fldl (%esp)
+; AVX512DQ_32-NEXT:    movl %ebp, %esp
+; AVX512DQ_32-NEXT:    popl %ebp
+; AVX512DQ_32-NEXT:    vzeroupper
+; AVX512DQ_32-NEXT:    retl
+;
+; AVX512F_32-LABEL: s64_to_d:
+; AVX512F_32:       # %bb.0:
+; AVX512F_32-NEXT:    pushl %ebp
+; AVX512F_32-NEXT:    movl %esp, %ebp
+; AVX512F_32-NEXT:    andl $-8, %esp
+; AVX512F_32-NEXT:    subl $8, %esp
+; AVX512F_32-NEXT:    fildll 8(%ebp)
+; AVX512F_32-NEXT:    fstpl (%esp)
+; AVX512F_32-NEXT:    fldl (%esp)
+; AVX512F_32-NEXT:    movl %ebp, %esp
+; AVX512F_32-NEXT:    popl %ebp
+; AVX512F_32-NEXT:    retl
+;
 ; SSE2_32-LABEL: s64_to_d:
 ; SSE2_32:       # %bb.0:
 ; SSE2_32-NEXT:    pushl %ebp
 ; SSE2_32-NEXT:    movl %esp, %ebp
 ; SSE2_32-NEXT:    andl $-8, %esp
 ; SSE2_32-NEXT:    subl $8, %esp
 ; SSE2_32-NEXT:    fildll 8(%ebp)
 ; SSE2_32-NEXT:    fstpl (%esp)