[SCEV] Add tests for missed NSW preservation during loop guard handling.

Add test coverage for missed simplification.

Author: fhahn

llvm/test/Analysis/ScalarEvolution/backedge-taken-count-guard-info.ll

@@ -69,4 +69,38 @@ exit:
   ret void
 }
 
+declare void @use(i32)
+
+define void @rewrite_preserve_add_nsw(i32 %a) {
+; CHECK-LABEL: 'rewrite_preserve_add_nsw'
+; CHECK-NEXT:  Classifying expressions for: @rewrite_preserve_add_nsw
+; CHECK-NEXT:    %add = add nsw i32 %a, 4
+; CHECK-NEXT:    --> (4 + %a)<nsw> U: [-2147483644,-2147483648) S: [-2147483644,-2147483648)
+; CHECK-NEXT:    %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
+; CHECK-NEXT:    --> {0,+,1}<nuw><%loop> U: [0,-2147483648) S: [0,-2147483648) Exits: (0 smax (4 + %a)<nsw>) LoopDispositions: { %loop: Computable }
+; CHECK-NEXT:    %iv.next = add i32 %iv, 1
+; CHECK-NEXT:    --> {1,+,1}<nuw><%loop> U: [1,-2147483647) S: [1,-2147483647) Exits: (1 + (0 smax (4 + %a)<nsw>))<nuw> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT:  Determining loop execution counts for: @rewrite_preserve_add_nsw
+; CHECK-NEXT:  Loop %loop: backedge-taken count is (0 smax (4 + %a)<nsw>)
+; CHECK-NEXT:  Loop %loop: constant max backedge-taken count is i32 2147483647
+; CHECK-NEXT:  Loop %loop: symbolic max backedge-taken count is (0 smax (4 + %a)<nsw>)
+; CHECK-NEXT:  Loop %loop: Trip multiple is 1
+;
+entry:
+  %add = add nsw i32 %a, 4
+  call void @use(i32 noundef %add)
+  %pre = icmp sgt i32 %a, -4
+  br i1 %pre, label %loop, label %exit
+
+loop:
+  %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
+  call void @clobber()
+  %iv.next = add i32 %iv, 1
+  %ec = icmp slt i32 %iv, %add
+  br i1 %ec, label %loop, label %exit
+
+exit:
+  ret void
+}
+
 declare void @clobber()

llvm/test/Transforms/IndVarSimplify/trip-count-expansion-loop-guard-preserve-nsw.ll

@@ -0,0 +1,47 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt -passes=indvars -S %s | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128-Fn32"
+
+define void @rewrite_preserve_add_nsw(i32 %a) {
+; CHECK-LABEL: define void @rewrite_preserve_add_nsw(
+; CHECK-SAME: i32 [[A:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[A]], 4
+; CHECK-NEXT:    call void @use(i32 noundef [[ADD]])
+; CHECK-NEXT:    [[PRE:%.*]] = icmp sgt i32 [[A]], -4
+; CHECK-NEXT:    br i1 [[PRE]], label [[LOOP_PREHEADER:%.*]], label [[EXIT:%.*]]
+; CHECK:       loop.preheader:
+; CHECK-NEXT:    [[SMAX:%.*]] = call i32 @llvm.smax.i32(i32 [[ADD]], i32 0)
+; CHECK-NEXT:    [[TMP0:%.*]] = add nuw i32 [[SMAX]], 1
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ [[IV_NEXT:%.*]], [[LOOP]] ], [ 0, [[LOOP_PREHEADER]] ]
+; CHECK-NEXT:    call void @clobber()
+; CHECK-NEXT:    [[IV_NEXT]] = add nuw i32 [[IV]], 1
+; CHECK-NEXT:    [[EC:%.*]] = icmp ne i32 [[IV_NEXT]], [[TMP0]]
+; CHECK-NEXT:    br i1 [[EC]], label [[LOOP]], label [[EXIT_LOOPEXIT:%.*]]
+; CHECK:       exit.loopexit:
+; CHECK-NEXT:    br label [[EXIT]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  %add = add nsw i32 %a, 4
+  call void @use(i32 noundef %add)
+  %pre = icmp sgt i32 %a, -4
+  br i1 %pre, label %loop, label %exit
+
+loop:
+  %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
+  call void @clobber()
+  %iv.next = add i32 %iv, 1
+  %ec = icmp slt i32 %iv, %add
+  br i1 %ec, label %loop, label %exit
+
+exit:
+  ret void
+}
+
+declare void @clobber()
+declare void @use(i32)