[ValueTracking] Add support for vector_reduce_{s,u}{min,max} in computeKnownBits

Previously missing. We compute by just applying the reduce function on
the knownbits of each element.

Closes llvm#88169

Author: goldsteinn

llvm/lib/Analysis/ValueTracking.cpp

@@ -1621,6 +1621,14 @@ static void computeKnownBitsFromOperator(const Operator *I,
         computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);
         Known = KnownBits::ssub_sat(Known, Known2);
         break;
+        // for min/max reduce, any bit common to each element in the input vec
+        // is set in the output.
+      case Intrinsic::vector_reduce_umax:
+      case Intrinsic::vector_reduce_umin:
+      case Intrinsic::vector_reduce_smax:
+      case Intrinsic::vector_reduce_smin:
+        computeKnownBits(I->getOperand(0), Known, Depth + 1, Q);
+        break;
       case Intrinsic::umin:
         computeKnownBits(I->getOperand(0), Known, Depth + 1, Q);
         computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);

llvm/test/Transforms/InstCombine/vector-reduce-min-max-known.ll

@@ -130,10 +130,7 @@ define i1 @vec_reduce_smin_non_zero_fail(<4 x i8> %xx) {
 
 define i8 @vec_reduce_umax_known0(<4 x i8> %xx) {
 ; CHECK-LABEL: @vec_reduce_umax_known0(
-; CHECK-NEXT:    [[X:%.*]] = or <4 x i8> [[XX:%.*]], <i8 1, i8 1, i8 1, i8 1>
-; CHECK-NEXT:    [[V:%.*]] = call i8 @llvm.vector.reduce.umax.v4i8(<4 x i8> [[X]])
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[V]], 1
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 1
 ;
   %x = or <4 x i8> %xx, <i8 1, i8 1, i8 1, i8 1>
   %v = call i8 @llvm.vector.reduce.umax(<4 x i8> %x)
@@ -182,10 +179,7 @@ define i8 @vec_reduce_umax_known_fail1(<4 x i8> %xx) {
 
 define i8 @vec_reduce_umin_known0(<4 x i8> %xx) {
 ; CHECK-LABEL: @vec_reduce_umin_known0(
-; CHECK-NEXT:    [[X:%.*]] = or <4 x i8> [[XX:%.*]], <i8 1, i8 1, i8 1, i8 1>
-; CHECK-NEXT:    [[V:%.*]] = call i8 @llvm.vector.reduce.umin.v4i8(<4 x i8> [[X]])
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[V]], 1
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 1
 ;
   %x = or <4 x i8> %xx, <i8 1, i8 1, i8 1, i8 1>
   %v = call i8 @llvm.vector.reduce.umin(<4 x i8> %x)
@@ -235,10 +229,7 @@ define i8 @vec_reduce_umin_known_fail1(<4 x i8> %xx) {
 
 define i8 @vec_reduce_smax_known(<4 x i8> %xx) {
 ; CHECK-LABEL: @vec_reduce_smax_known(
-; CHECK-NEXT:    [[X:%.*]] = or <4 x i8> [[XX:%.*]], <i8 4, i8 4, i8 4, i8 5>
-; CHECK-NEXT:    [[V:%.*]] = call i8 @llvm.vector.reduce.smax.v4i8(<4 x i8> [[X]])
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[V]], 4
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 4
 ;
   %x = or <4 x i8> %xx, <i8 4, i8 4, i8 4, i8 5>
   %v = call i8 @llvm.vector.reduce.smax(<4 x i8> %x)
@@ -261,10 +252,7 @@ define i8 @vec_reduce_smax_known_fail(<4 x i8> %xx) {
 
 define i8 @vec_reduce_smin_known(<4 x i8> %xx) {
 ; CHECK-LABEL: @vec_reduce_smin_known(
-; CHECK-NEXT:    [[X:%.*]] = or <4 x i8> [[XX:%.*]], <i8 8, i8 24, i8 56, i8 9>
-; CHECK-NEXT:    [[V:%.*]] = call i8 @llvm.vector.reduce.smin.v4i8(<4 x i8> [[X]])
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[V]], 8
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 8
 ;
   %x = or <4 x i8> %xx, <i8 8, i8 24, i8 56, i8 9>
   %v = call i8 @llvm.vector.reduce.smin(<4 x i8> %x)