[llvm] [LoopPeel] LCSSA form is destroyed by LoopPeel, preserve it (PR #78696)

[Vedant Paranjape via llvm-commits]

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@@ -0,0 +1,58 @@
+; RUN: opt -passes=loop-unroll -unroll-peel-count=2 -S -disable-output -debug-only=loop-unroll < %s 2>&1 | FileCheck %s
+; REQUIRES: asserts
+
+define void @test() {
+; CHECK-LABEL: Loop Unroll: F[test] Loop %loop3
+; CHECK-NEXT:    Loop Size = 7
+; CHECK-NEXT:  PEELING loop %loop3 with iteration count 2!
+; CHECK-NEXT:  Loop Unroll: F[test] Loop %loop2
+; CHECK-NEXT:    Loop Size = 28
+; CHECK-NEXT:  PEELING loop %loop2 with iteration count 2!
+; CHECK-NEXT:  Loop Unroll: F[test] Loop %loop4
+; CHECK-NEXT:    Loop Size = 3
+; CHECK-NEXT:  PEELING loop %loop4 with iteration count 2!
+; CHECK-NEXT:  Loop Unroll: F[test] Loop %loop1
+; CHECK-NEXT:    Loop Size = 95
+; CHECK-NEXT:  PEELING loop %loop1 with iteration count 2!
+entry:
+  br label %loop1
+
+loop1:
+  %phi = phi i32 [ 1, %entry ], [ 0, %loop1.latch ]
+  br label %loop2
+
+loop2:
+  %phi3 = phi i64 [ 0, %loop1 ], [ %sext, %loop2.latch ]
+  br label %loop3
+
+loop3:
+  %phi5 = phi i64 [ %phi3, %loop2 ], [ %sext, %loop3.latch ]
+  %phi6 = phi i32 [ 1, %loop2 ], [ %add10, %loop3.latch ]
+  %trunc = trunc i64 %phi5 to i32
+  br i1 true, label %loop3.latch, label %exit
+
+loop3.latch:
+  %add = add i32 1, %phi
+  %sext = sext i32 %add to i64
+  %add10 = add i32 %phi6, 1
+  %icmp = icmp ugt i32 %add10, 2
+  br i1 %icmp, label %loop2.latch, label %loop3
+
+loop2.latch:
+  br i1 false, label %loop4.preheader, label %loop2
+
+loop4.preheader:
+  br label %loop4
+
+loop4:
+  br i1 false, label %loop1.latch, label %loop4
+
+loop1.latch:
+  br label %loop1
+
+exit:
+  %phi8 = phi i32 [ %trunc, %loop3 ]
+  ret void
+}
+;; NOTE: These prefixes are unused and the list is autogenerated. Do not add tests below this line:
+; CHECK: {{.*}}
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vedantparanjape-amd wrote:

done!

https://github.com/llvm/llvm-project/pull/78696