[GlobalISel][AArch64] Fix fptoi.sat lowering. (llvm#127901)

The SDAG version uses fminnum/fmaxnum, in converting it to fcmp+select
it appears the order of the operands was chosen badly. This switches the
conditions used to keep the constant on the RHS.

(cherry picked from commit 70ed381)

Author: davemgreen

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

@@ -7801,13 +7801,13 @@ LegalizerHelper::lowerFPTOINT_SAT(MachineInstr &MI) {
   if (AreExactFloatBounds) {
     // Clamp Src by MinFloat from below. If Src is NaN the result is MinFloat.
     auto MaxC = MIRBuilder.buildFConstant(SrcTy, MinFloat);
-    auto MaxP = MIRBuilder.buildFCmp(CmpInst::FCMP_ULT,
+    auto MaxP = MIRBuilder.buildFCmp(CmpInst::FCMP_OGT,
                                      SrcTy.changeElementSize(1), Src, MaxC);
     auto Max = MIRBuilder.buildSelect(SrcTy, MaxP, Src, MaxC);
     // Clamp by MaxFloat from above. NaN cannot occur.
     auto MinC = MIRBuilder.buildFConstant(SrcTy, MaxFloat);
     auto MinP =
-        MIRBuilder.buildFCmp(CmpInst::FCMP_OGT, SrcTy.changeElementSize(1), Max,
+        MIRBuilder.buildFCmp(CmpInst::FCMP_OLT, SrcTy.changeElementSize(1), Max,
                              MinC, MachineInstr::FmNoNans);
     auto Min =
         MIRBuilder.buildSelect(SrcTy, MinP, Max, MinC, MachineInstr::FmNoNans);

llvm/test/CodeGen/AArch64/fptosi-sat-scalar.ll

@@ -987,25 +987,25 @@ define i32 @test_signed_f128_i32(fp128 %f) {
 ; CHECK-GI-NEXT:    adrp x8, .LCPI30_1
 ; CHECK-GI-NEXT:    str q0, [sp] // 16-byte Folded Spill
 ; CHECK-GI-NEXT:    ldr q1, [x8, :lo12:.LCPI30_1]
-; CHECK-GI-NEXT:    bl __getf2
+; CHECK-GI-NEXT:    bl __gttf2
 ; CHECK-GI-NEXT:    ldr q0, [sp] // 16-byte Folded Reload
 ; CHECK-GI-NEXT:    cmp w0, #0
 ; CHECK-GI-NEXT:    mov x9, #-4603241769126068224 // =0xc01e000000000000
 ; CHECK-GI-NEXT:    fmov x8, d0
-; CHECK-GI-NEXT:    csel x19, x8, xzr, lt
+; CHECK-GI-NEXT:    csel x19, x8, xzr, gt
 ; CHECK-GI-NEXT:    mov x8, v0.d[1]
 ; CHECK-GI-NEXT:    mov v0.d[0], x19
-; CHECK-GI-NEXT:    csel x20, x8, x9, lt
+; CHECK-GI-NEXT:    csel x20, x8, x9, gt
 ; CHECK-GI-NEXT:    adrp x8, .LCPI30_0
 ; CHECK-GI-NEXT:    mov v0.d[1], x20
 ; CHECK-GI-NEXT:    ldr q1, [x8, :lo12:.LCPI30_0]
-; CHECK-GI-NEXT:    bl __gttf2
+; CHECK-GI-NEXT:    bl __lttf2
 ; CHECK-GI-NEXT:    cmp w0, #0
-; CHECK-GI-NEXT:    csel x8, x19, xzr, gt
+; CHECK-GI-NEXT:    csel x8, x19, xzr, lt
 ; CHECK-GI-NEXT:    mov v0.d[0], x8
 ; CHECK-GI-NEXT:    mov x8, #281474976448512 // =0xfffffffc0000
 ; CHECK-GI-NEXT:    movk x8, #16413, lsl #48
-; CHECK-GI-NEXT:    csel x8, x20, x8, gt
+; CHECK-GI-NEXT:    csel x8, x20, x8, lt
 ; CHECK-GI-NEXT:    mov v0.d[1], x8
 ; CHECK-GI-NEXT:    bl __fixtfsi
 ; CHECK-GI-NEXT:    ldr q0, [sp] // 16-byte Folded Reload