[LoopPeel] Add test for peeling last iteration with non-trivial BTC.

Additional test to #140792 with
different SCEV expansion costs.

Author: fhahn

llvm/test/Transforms/LoopUnroll/peel-last-iteration-expansion-cost.ll

@@ -0,0 +1,61 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -p loop-unroll -scev-cheap-expansion-budget=2 -S %s | FileCheck --check-prefix=BUDGET2 %s
+; RUN: opt -p loop-unroll -scev-cheap-expansion-budget=3 -S %s | FileCheck --check-prefix=BUDGET3 %s
+
+define i32 @test_expansion_cost_2(i32 %start, i32 %end) {
+; BUDGET2-LABEL: define i32 @test_expansion_cost_2(
+; BUDGET2-SAME: i32 [[START:%.*]], i32 [[END:%.*]]) {
+; BUDGET2-NEXT:  [[ENTRY:.*]]:
+; BUDGET2-NEXT:    [[SUB:%.*]] = add i32 [[END]], -1
+; BUDGET2-NEXT:    br label %[[LOOP_HEADER:.*]]
+; BUDGET2:       [[LOOP_HEADER]]:
+; BUDGET2-NEXT:    [[IV:%.*]] = phi i32 [ [[START]], %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP_LATCH:.*]] ]
+; BUDGET2-NEXT:    [[C:%.*]] = icmp eq i32 [[IV]], [[SUB]]
+; BUDGET2-NEXT:    br i1 [[C]], label %[[THEN:.*]], label %[[LOOP_LATCH]]
+; BUDGET2:       [[THEN]]:
+; BUDGET2-NEXT:    br label %[[LOOP_LATCH]]
+; BUDGET2:       [[LOOP_LATCH]]:
+; BUDGET2-NEXT:    [[IV_NEXT]] = add nsw i32 [[IV]], 1
+; BUDGET2-NEXT:    [[EC:%.*]] = icmp eq i32 [[IV_NEXT]], [[END]]
+; BUDGET2-NEXT:    br i1 [[EC]], label %[[EXIT:.*]], label %[[LOOP_HEADER]]
+; BUDGET2:       [[EXIT]]:
+; BUDGET2-NEXT:    ret i32 0
+;
+; BUDGET3-LABEL: define i32 @test_expansion_cost_2(
+; BUDGET3-SAME: i32 [[START:%.*]], i32 [[END:%.*]]) {
+; BUDGET3-NEXT:  [[ENTRY:.*]]:
+; BUDGET3-NEXT:    [[SUB:%.*]] = add i32 [[END]], -1
+; BUDGET3-NEXT:    br label %[[LOOP_HEADER:.*]]
+; BUDGET3:       [[LOOP_HEADER]]:
+; BUDGET3-NEXT:    [[TMP3:%.*]] = phi i32 [ [[START]], %[[ENTRY]] ], [ [[IV_NEXT_PEEL:%.*]], %[[LOOP_LATCH:.*]] ]
+; BUDGET3-NEXT:    [[C_PEEL:%.*]] = icmp eq i32 [[TMP3]], [[SUB]]
+; BUDGET3-NEXT:    br i1 [[C_PEEL]], label %[[THEN:.*]], label %[[LOOP_LATCH]]
+; BUDGET3:       [[THEN]]:
+; BUDGET3-NEXT:    br label %[[LOOP_LATCH]]
+; BUDGET3:       [[LOOP_LATCH]]:
+; BUDGET3-NEXT:    [[IV_NEXT_PEEL]] = add nsw i32 [[TMP3]], 1
+; BUDGET3-NEXT:    [[EC_PEEL:%.*]] = icmp eq i32 [[IV_NEXT_PEEL]], [[END]]
+; BUDGET3-NEXT:    br i1 [[EC_PEEL]], label %[[EXIT:.*]], label %[[LOOP_HEADER]]
+; BUDGET3:       [[EXIT]]:
+; BUDGET3-NEXT:    ret i32 0
+;
+entry:
+  %sub = add i32 %end, -1
+  br label %loop.header
+
+loop.header:
+  %iv = phi i32 [ %start, %entry ], [ %iv.next, %loop.latch ]
+  %c = icmp eq i32 %iv, %sub
+  br i1 %c, label %then, label %loop.latch
+
+then:
+  br label %loop.latch
+
+loop.latch:
+  %iv.next = add nsw i32 %iv, 1
+  %ec = icmp eq i32 %iv.next, %end
+  br i1 %ec, label %exit, label %loop.header
+
+exit:
+  ret i32 0
+}