[GlobalIsel] Combine select to integer min max more (#92570)

Author: Thorsten Schütt

llvm/include/llvm/Target/GlobalISel/Combine.td

@@ -1309,7 +1309,7 @@ def select_to_minmax: GICombineRule<
 
 def select_to_iminmax: GICombineRule<
   (defs root:$root, build_fn_matchinfo:$info),
-  (match (G_ICMP $tst, $tst1, $x, $y),
+  (match (G_ICMP $tst, $tst1, $a, $b),
          (G_SELECT $root, $tst, $x, $y),
          [{ return Helper.matchSelectIMinMax(${root}, ${info}); }]),
   (apply [{ Helper.applyBuildFnMO(${root}, ${info}); }])>;

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

@@ -6772,13 +6772,20 @@ bool CombinerHelper::matchSelectIMinMax(const MachineOperand &MO,
   if (CmpInst::isEquality(Pred))
     return false;
 
-  [[maybe_unused]] Register CmpLHS = Cmp->getLHSReg();
-  [[maybe_unused]] Register CmpRHS = Cmp->getRHSReg();
+  Register CmpLHS = Cmp->getLHSReg();
+  Register CmpRHS = Cmp->getRHSReg();
+
+  // We can swap CmpLHS and CmpRHS for higher hitrate.
+  if (True == CmpRHS && False == CmpLHS) {
+    std::swap(CmpLHS, CmpRHS);
+    Pred = CmpInst::getSwappedPredicate(Pred);
+  }
 
   // (icmp X, Y) ? X : Y -> integer minmax.
   // see matchSelectPattern in ValueTracking.
   // Legality between G_SELECT and integer minmax can differ.
-  assert(True == CmpLHS && False == CmpRHS && "unexpected MIR pattern");
+  if (True != CmpLHS || False != CmpRHS)
+    return false;
 
   switch (Pred) {
   case ICmpInst::ICMP_UGT:

llvm/test/CodeGen/AArch64/GlobalISel/combine-select.mir

@@ -911,8 +911,7 @@ body:             |
     ; CHECK-NEXT: %f1:_(s32) = G_TRUNC [[COPY1]](s64)
     ; CHECK-NEXT: %t:_(<4 x s32>) = G_BUILD_VECTOR %t1(s32), %t1(s32), %t1(s32), %t1(s32)
     ; CHECK-NEXT: %f:_(<4 x s32>) = G_BUILD_VECTOR %f1(s32), %f1(s32), %f1(s32), %f1(s32)
-    ; CHECK-NEXT: %c:_(<4 x s32>) = G_ICMP intpred(sle), %f(<4 x s32>), %t
-    ; CHECK-NEXT: %sel:_(<4 x s32>) = exact G_SELECT %c(<4 x s32>), %t, %f
+    ; CHECK-NEXT: %sel:_(<4 x s32>) = G_SMAX %t, %f
     ; CHECK-NEXT: $q0 = COPY %sel(<4 x s32>)
     %0:_(s64) = COPY $x0
     %1:_(s64) = COPY $x1