[LSR] Add test for multi-edge latch (NFC)

This is additional test coverage for D72519.

Author: nikic

llvm/test/Transforms/LoopStrengthReduce/multi-edge-latch.ll

@@ -0,0 +1,48 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -loop-reduce < %s | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @test(i8* %p.base, i8 %x) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    switch i8 [[X:%.*]], label [[WHILE_END:%.*]] [
+; CHECK-NEXT:    i8 10, label [[WHILE_BODY_PREHEADER:%.*]]
+; CHECK-NEXT:    i8 20, label [[WHILE_BODY_PREHEADER]]
+; CHECK-NEXT:    ]
+; CHECK:       while.body.preheader:
+; CHECK-NEXT:    [[SCEVGEP:%.*]] = getelementptr i8, i8* [[P_BASE:%.*]], i64 1
+; CHECK-NEXT:    br label [[WHILE_BODY:%.*]]
+; CHECK:       while.body:
+; CHECK-NEXT:    [[LSR_IV:%.*]] = phi i8* [ [[SCEVGEP1:%.*]], [[WHILE_BODY_BACKEDGE:%.*]] ], [ [[SCEVGEP]], [[WHILE_BODY_PREHEADER]] ]
+; CHECK-NEXT:    [[Y:%.*]] = load i8, i8* [[LSR_IV]], align 1
+; CHECK-NEXT:    switch i8 [[Y]], label [[WHILE_END_LOOPEXIT:%.*]] [
+; CHECK-NEXT:    i8 10, label [[WHILE_BODY_BACKEDGE]]
+; CHECK-NEXT:    i8 20, label [[WHILE_BODY_BACKEDGE]]
+; CHECK-NEXT:    ]
+; CHECK:       while.body.backedge:
+; CHECK-NEXT:    [[SCEVGEP1]] = getelementptr i8, i8* [[LSR_IV]], i64 1
+; CHECK-NEXT:    br label [[WHILE_BODY]]
+; CHECK:       while.end.loopexit:
+; CHECK-NEXT:    br label [[WHILE_END]]
+; CHECK:       while.end:
+; CHECK-NEXT:    ret void
+;
+entry:
+  switch i8 %x, label %while.end [
+  i8 10, label %while.body
+  i8 20, label %while.body
+  ]
+
+while.body:
+  %p = phi i8* [ %p.inc, %while.body ], [ %p.inc, %while.body ], [ %p.base, %entry ], [ %p.base, %entry ]
+  %p.inc = getelementptr inbounds i8, i8* %p, i64 1
+  %y = load i8, i8* %p.inc, align 1
+  switch i8 %y, label %while.end [
+  i8 10, label %while.body
+  i8 20, label %while.body
+  ]
+
+while.end:
+  ret void
+}