[LoopPeel] Insert new phis before first non-PHI when peeling last iter.

Make sure the new phis are inserted before any non-phi instructions.
This fixes a crash when dbg_value instructions are present in the
original exit block.

Author: fhahn

llvm/lib/Transforms/Utils/LoopPeel.cpp

@@ -922,7 +922,7 @@ static void cloneLoopBlocks(
     // InsertTop, using the incoming value from the preheader for the original
     // preheader (when skipping the main loop) and the incoming value from the
     // latch for the latch (when continuing from the main loop).
-    IRBuilder<> B(InsertTop->getTerminator());
+    IRBuilder<> B(InsertTop, InsertTop->getFirstNonPHIIt());
     for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
       PHINode *NewPHI = cast<PHINode>(VMap[&*I]);
       PHINode *PN = B.CreatePHI(NewPHI->getType(), 2);

llvm/test/Transforms/LoopUnroll/peel-last-iteration-debug.ll

@@ -0,0 +1,76 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -p loop-unroll -unroll-full-max-count=0 -S %s | FileCheck %s
+
+declare void @foo(i32)
+
+define void @test_dbg_value_in_exit_block() {
+; CHECK-LABEL: define void @test_dbg_value_in_exit_block() {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    br label %[[LOOP:.*]]
+; CHECK:       [[LOOP]]:
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[INC:%.*]], %[[LOOP]] ]
+; CHECK-NEXT:    call void @foo(i32 0)
+; CHECK-NEXT:    [[INC]] = add nuw nsw i32 [[IV]], 1
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i32 [[INC]], 20
+; CHECK-NEXT:    br i1 [[EXITCOND]], label %[[LOOP]], label %[[EXIT_PEEL_BEGIN:.*]], !llvm.loop [[LOOP4:![0-9]+]]
+; CHECK:       [[EXIT_PEEL_BEGIN]]:
+; CHECK-NEXT:    [[TMP0:%.*]] = phi i32 [ [[INC]], %[[LOOP]] ]
+; CHECK-NEXT:      #dbg_value(float poison, [[META6:![0-9]+]], !DIExpression(), [[META11:![0-9]+]])
+; CHECK-NEXT:    br label %[[LOOP_PEEL:.*]]
+; CHECK:       [[LOOP_PEEL]]:
+; CHECK-NEXT:    [[CMP2_PEEL:%.*]] = icmp eq i32 [[TMP0]], 20
+; CHECK-NEXT:    [[SEL_PEEL:%.*]] = select i1 [[CMP2_PEEL]], i32 1, i32 0
+; CHECK-NEXT:    call void @foo(i32 [[SEL_PEEL]])
+; CHECK-NEXT:    [[INC_PEEL:%.*]] = add i32 [[TMP0]], 1
+; CHECK-NEXT:    [[EXITCOND_PEEL:%.*]] = icmp ne i32 [[INC_PEEL]], 21
+; CHECK-NEXT:    br i1 [[EXITCOND_PEEL]], label %[[EXIT_PEEL_NEXT:.*]], label %[[EXIT_PEEL_NEXT]]
+; CHECK:       [[EXIT_PEEL_NEXT]]:
+; CHECK-NEXT:    br label %[[LOOP_PEEL_NEXT:.*]]
+; CHECK:       [[LOOP_PEEL_NEXT]]:
+; CHECK-NEXT:    br label %[[EXIT:.*]]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i32 [ 0, %entry ], [ %inc, %loop ]
+  %cmp2 = icmp eq i32 %iv, 20
+  %sel = select i1 %cmp2, i32 1, i32 0
+  call void @foo(i32 %sel)
+  %inc = add i32 %iv, 1
+  %exitcond = icmp ne i32 %inc, 21
+  br i1 %exitcond, label %loop, label %exit
+
+exit:
+    #dbg_value(float poison, !4, !DIExpression(), !9)
+  ret void
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 21.0.0git", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "repro.c", directory: "/", checksumkind: CSK_MD5, checksum: "3a182b2d218eb10b64164b06427cef3c")
+!2 = !{}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !DILocalVariable(name: "m_2", scope: !5, file: !1, line: 4, type: !8)
+!5 = distinct !DISubprogram(name: "test_dbg_value_in_exit_block", scope: !1, file: !1, line: 3, type: !6, scopeLine: 3, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!6 = !DISubroutineType(types: !7)
+!7 = !{null}
+!8 = !DIBasicType(name: "float", size: 32, encoding: DW_ATE_float)
+!9 = !DILocation(line: 0, scope: !5)
+;.
+; CHECK: [[META0:![0-9]+]] = distinct !DICompileUnit(language: DW_LANG_C11, file: [[META1:![0-9]+]], producer: "{{.*}}clang version {{.*}}", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: [[META2:![0-9]+]], splitDebugInlining: false, nameTableKind: None)
+; CHECK: [[META1]] = !DIFile(filename: "{{.*}}repro.c", directory: {{.*}})
+; CHECK: [[META2]] = !{}
+; CHECK: [[LOOP4]] = distinct !{[[LOOP4]], [[META5:![0-9]+]]}
+; CHECK: [[META5]] = !{!"llvm.loop.peeled.count", i32 1}
+; CHECK: [[META6]] = !DILocalVariable(name: "m_2", scope: [[META7:![0-9]+]], file: [[META1]], line: 4, type: [[META10:![0-9]+]])
+; CHECK: [[META7]] = distinct !DISubprogram(name: "test_dbg_value_in_exit_block", scope: [[META1]], file: [[META1]], line: 3, type: [[META8:![0-9]+]], scopeLine: 3, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: [[META0]], retainedNodes: [[META2]])
+; CHECK: [[META8]] = !DISubroutineType(types: [[META9:![0-9]+]])
+; CHECK: [[META9]] = !{null}
+; CHECK: [[META10]] = !DIBasicType(name: "float", size: 32, encoding: DW_ATE_float)
+; CHECK: [[META11]] = !DILocation(line: 0, scope: [[META7]])
+;.