[Transforms] add phase ordering tests for min/max/abs; NFC

Test that instcombine and early-cse can cooperate
to reduce sequences of select patterns that are not
composed of the same underlying instructions.

There's a bug in EarlyCSE (PR41083), and we can test
how much a possible fix (D74285) may affect optimization.

(cherry picked from commit 0ad6e72)

Author: rotateright

llvm/test/Transforms/PhaseOrdering/min-max-abs-cse.ll

@@ -0,0 +1,87 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -S -O1 | FileCheck %s
+; RUN: opt -passes='default<O1>' -S < %s  | FileCheck %s
+
+; In all tests, expect instcombine to canonicalize the select patterns
+; for min/max/abs to allow CSE and subsequent simplification.
+
+; sub (smax a,b), (smax a,b) --> 0
+
+define i8 @smax_nsw(i8 %a, i8 %b) {
+; CHECK-LABEL: @smax_nsw(
+; CHECK-NEXT:    ret i8 0
+;
+  %sub = sub nsw i8 %a, %b
+  %cmp1 = icmp slt i8 %a, %b
+  %cmp2 = icmp sgt i8 %sub, 0
+  %m1 = select i1 %cmp1, i8 0, i8 %sub
+  %m2 = select i1 %cmp2, i8 %sub, i8 0
+  %r = sub i8 %m2, %m1
+  ret i8 %r
+}
+
+; or (abs a), (abs a) --> abs a
+
+define i8 @abs_swapped(i8 %a) {
+; CHECK-LABEL: @abs_swapped(
+; CHECK-NEXT:    [[NEG:%.*]] = sub i8 0, [[A:%.*]]
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp slt i8 [[A]], 0
+; CHECK-NEXT:    [[M1:%.*]] = select i1 [[CMP1]], i8 [[NEG]], i8 [[A]]
+; CHECK-NEXT:    ret i8 [[M1]]
+;
+  %neg = sub i8 0, %a
+  %cmp1 = icmp sgt i8 %a, 0
+  %cmp2 = icmp slt i8 %a, 0
+  %m1 = select i1 %cmp1, i8 %a, i8 %neg
+  %m2 = select i1 %cmp2, i8 %neg, i8 %a
+  %r = or i8 %m2, %m1
+  ret i8 %r
+}
+
+; xor (nabs a), (nabs a) --> 0
+
+define i8 @nabs_swapped(i8 %a) {
+; CHECK-LABEL: @nabs_swapped(
+; CHECK-NEXT:    ret i8 0
+;
+  %neg = sub i8 0, %a
+  %cmp1 = icmp slt i8 %a, 0
+  %cmp2 = icmp sgt i8 %a, 0
+  %m1 = select i1 %cmp1, i8 %a, i8 %neg
+  %m2 = select i1 %cmp2, i8 %neg, i8 %a
+  %r = xor i8 %m2, %m1
+  ret i8 %r
+}
+
+; xor (abs a), (abs a) --> 0
+
+define i8 @abs_different_constants(i8 %a) {
+; CHECK-LABEL: @abs_different_constants(
+; CHECK-NEXT:    ret i8 0
+;
+  %neg = sub i8 0, %a
+  %cmp1 = icmp sgt i8 %a, -1
+  %cmp2 = icmp slt i8 %a, 0
+  %m1 = select i1 %cmp1, i8 %a, i8 %neg
+  %m2 = select i1 %cmp2, i8 %neg, i8 %a
+  %r = xor i8 %m2, %m1
+  ret i8 %r
+}
+
+; or (nabs a), (nabs a) --> nabs a
+
+define i8 @nabs_different_constants(i8 %a) {
+; CHECK-LABEL: @nabs_different_constants(
+; CHECK-NEXT:    [[NEG:%.*]] = sub i8 0, [[A:%.*]]
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp slt i8 [[A]], 0
+; CHECK-NEXT:    [[M1:%.*]] = select i1 [[CMP1]], i8 [[A]], i8 [[NEG]]
+; CHECK-NEXT:    ret i8 [[M1]]
+;
+  %neg = sub i8 0, %a
+  %cmp1 = icmp slt i8 %a, 0
+  %cmp2 = icmp sgt i8 %a, -1
+  %m1 = select i1 %cmp1, i8 %a, i8 %neg
+  %m2 = select i1 %cmp2, i8 %neg, i8 %a
+  %r = or i8 %m2, %m1
+  ret i8 %r
+}