[GISel][RISCV] Use isSExtCheaperThanZExt when widening G_UMAX/G_UMIN. (#120041)

Similar to what we do for unsigned comparisons after #120032.

Author: topperc

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

@@ -2884,15 +2884,12 @@ LegalizerHelper::widenScalar(MachineInstr &MI, unsigned TypeIdx, LLT WideTy) {
     return Legalized;
   case TargetOpcode::G_UDIV:
   case TargetOpcode::G_UREM:
-  case TargetOpcode::G_UMIN:
-  case TargetOpcode::G_UMAX:
     Observer.changingInstr(MI);
     widenScalarSrc(MI, WideTy, 1, TargetOpcode::G_ZEXT);
     widenScalarSrc(MI, WideTy, 2, TargetOpcode::G_ZEXT);
     widenScalarDst(MI, WideTy);
     Observer.changedInstr(MI);
     return Legalized;
-
   case TargetOpcode::G_UDIVREM:
     Observer.changingInstr(MI);
     widenScalarSrc(MI, WideTy, 2, TargetOpcode::G_ZEXT);
@@ -2901,6 +2898,24 @@ LegalizerHelper::widenScalar(MachineInstr &MI, unsigned TypeIdx, LLT WideTy) {
     widenScalarDst(MI, WideTy, 1);
     Observer.changedInstr(MI);
     return Legalized;
+  case TargetOpcode::G_UMIN:
+  case TargetOpcode::G_UMAX: {
+    LLT Ty = MRI.getType(MI.getOperand(0).getReg());
+
+    auto &Ctx = MIRBuilder.getMF().getFunction().getContext();
+    unsigned ExtOpc =
+        TLI.isSExtCheaperThanZExt(getApproximateEVTForLLT(Ty, Ctx),
+                                  getApproximateEVTForLLT(WideTy, Ctx))
+            ? TargetOpcode::G_SEXT
+            : TargetOpcode::G_ZEXT;
+
+    Observer.changingInstr(MI);
+    widenScalarSrc(MI, WideTy, 1, ExtOpc);
+    widenScalarSrc(MI, WideTy, 2, ExtOpc);
+    widenScalarDst(MI, WideTy);
+    Observer.changedInstr(MI);
+    return Legalized;
+  }
 
   case TargetOpcode::G_SELECT:
     Observer.changingInstr(MI);

llvm/test/CodeGen/RISCV/GlobalISel/legalizer/legalize-umax-rv64.mir

@@ -99,11 +99,12 @@ body:             |
     ; RV64ZBB-LABEL: name: umax_i32
     ; RV64ZBB: [[COPY:%[0-9]+]]:_(s64) = COPY $x10
     ; RV64ZBB-NEXT: [[COPY1:%[0-9]+]]:_(s64) = COPY $x11
+    ; RV64ZBB-NEXT: [[SEXT_INREG:%[0-9]+]]:_(s64) = G_SEXT_INREG [[COPY]], 32
+    ; RV64ZBB-NEXT: [[SEXT_INREG1:%[0-9]+]]:_(s64) = G_SEXT_INREG [[COPY1]], 32
+    ; RV64ZBB-NEXT: [[UMAX:%[0-9]+]]:_(s64) = G_UMAX [[SEXT_INREG]], [[SEXT_INREG1]]
     ; RV64ZBB-NEXT: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 4294967295
-    ; RV64ZBB-NEXT: [[AND:%[0-9]+]]:_(s64) = G_AND [[COPY]], [[C]]
-    ; RV64ZBB-NEXT: [[AND1:%[0-9]+]]:_(s64) = G_AND [[COPY1]], [[C]]
-    ; RV64ZBB-NEXT: [[UMAX:%[0-9]+]]:_(s64) = G_UMAX [[AND]], [[AND1]]
-    ; RV64ZBB-NEXT: $x10 = COPY [[UMAX]](s64)
+    ; RV64ZBB-NEXT: [[AND:%[0-9]+]]:_(s64) = G_AND [[UMAX]], [[C]]
+    ; RV64ZBB-NEXT: $x10 = COPY [[AND]](s64)
     ; RV64ZBB-NEXT: PseudoRET implicit $x10
     %0:_(s64) = COPY $x10
     %1:_(s64) = COPY $x11

llvm/test/CodeGen/RISCV/GlobalISel/legalizer/legalize-umin-rv64.mir

@@ -99,11 +99,12 @@ body:             |
     ; RV64ZBB-LABEL: name: umin_i32
     ; RV64ZBB: [[COPY:%[0-9]+]]:_(s64) = COPY $x10
     ; RV64ZBB-NEXT: [[COPY1:%[0-9]+]]:_(s64) = COPY $x11
+    ; RV64ZBB-NEXT: [[SEXT_INREG:%[0-9]+]]:_(s64) = G_SEXT_INREG [[COPY]], 32
+    ; RV64ZBB-NEXT: [[SEXT_INREG1:%[0-9]+]]:_(s64) = G_SEXT_INREG [[COPY1]], 32
+    ; RV64ZBB-NEXT: [[UMIN:%[0-9]+]]:_(s64) = G_UMIN [[SEXT_INREG]], [[SEXT_INREG1]]
     ; RV64ZBB-NEXT: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 4294967295
-    ; RV64ZBB-NEXT: [[AND:%[0-9]+]]:_(s64) = G_AND [[COPY]], [[C]]
-    ; RV64ZBB-NEXT: [[AND1:%[0-9]+]]:_(s64) = G_AND [[COPY1]], [[C]]
-    ; RV64ZBB-NEXT: [[UMIN:%[0-9]+]]:_(s64) = G_UMIN [[AND]], [[AND1]]
-    ; RV64ZBB-NEXT: $x10 = COPY [[UMIN]](s64)
+    ; RV64ZBB-NEXT: [[AND:%[0-9]+]]:_(s64) = G_AND [[UMIN]], [[C]]
+    ; RV64ZBB-NEXT: $x10 = COPY [[AND]](s64)
     ; RV64ZBB-NEXT: PseudoRET implicit $x10
     %0:_(s64) = COPY $x10
     %1:_(s64) = COPY $x11

llvm/test/CodeGen/RISCV/GlobalISel/rv64zbb.ll

@@ -987,12 +987,7 @@ define signext i32 @minu_i32(i32 signext %a, i32 signext %b) nounwind {
 ;
 ; RV64ZBB-LABEL: minu_i32:
 ; RV64ZBB:       # %bb.0:
-; RV64ZBB-NEXT:    slli a0, a0, 32
-; RV64ZBB-NEXT:    slli a1, a1, 32
-; RV64ZBB-NEXT:    srli a0, a0, 32
-; RV64ZBB-NEXT:    srli a1, a1, 32
 ; RV64ZBB-NEXT:    minu a0, a0, a1
-; RV64ZBB-NEXT:    sext.w a0, a0
 ; RV64ZBB-NEXT:    ret
   %cmp = icmp ult i32 %a, %b
   %cond = select i1 %cmp, i32 %a, i32 %b
@@ -1031,12 +1026,7 @@ define signext i32 @maxu_i32(i32 signext %a, i32 signext %b) nounwind {
 ;
 ; RV64ZBB-LABEL: maxu_i32:
 ; RV64ZBB:       # %bb.0:
-; RV64ZBB-NEXT:    slli a0, a0, 32
-; RV64ZBB-NEXT:    slli a1, a1, 32
-; RV64ZBB-NEXT:    srli a0, a0, 32
-; RV64ZBB-NEXT:    srli a1, a1, 32
 ; RV64ZBB-NEXT:    maxu a0, a0, a1
-; RV64ZBB-NEXT:    sext.w a0, a0
 ; RV64ZBB-NEXT:    ret
   %cmp = icmp ugt i32 %a, %b
   %cond = select i1 %cmp, i32 %a, i32 %b