[SCEV] Make sure LCSSA is preserved when re-using phi if needed.

If we insert a new add instruction, it may introduce a new use outside
the loop that contains the phi node we re-use. Use fixupLCSSAFormFor to
fix LCSSA form, if needed.

This fixes a crash reported in
#147824 (comment).

Author: fhahn

llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp

@@ -1257,7 +1257,7 @@ Value *SCEVExpander::tryToReuseLCSSAPhi(const SCEVAddRecExpr *S) {
     assert(Diff->getType()->isIntegerTy() &&
            "difference must be of integer type");
     Value *DiffV = expand(Diff);
-    Value *BaseV = &PN;
+    Value *BaseV = fixupLCSSAFormFor(&PN);
     if (PhiTy->isPointerTy()) {
       if (STy->isPointerTy())
         return Builder.CreatePtrAdd(BaseV, DiffV);

llvm/test/Transforms/LoopIdiom/reuse-lcssa-phi-scev-expansion.ll

@@ -111,11 +111,12 @@ define ptr @test_lcssa_reuse_preserve_lcssa() {
 ; CHECK-NEXT:    [[EC_1:%.*]] = call i1 @cond()
 ; CHECK-NEXT:    br i1 [[EC_1]], label %[[THEN:.*]], label %[[LOOP_1]]
 ; CHECK:       [[THEN]]:
-; CHECK-NEXT:    [[IV_1_LCSSA:%.*]] = phi ptr [ [[IV_1]], %[[LOOP_1]] ]
+; CHECK-NEXT:    [[IV_1_LCSSA1:%.*]] = phi ptr [ [[IV_1]], %[[LOOP_1]] ]
 ; CHECK-NEXT:    [[C_2:%.*]] = call i1 @cond()
 ; CHECK-NEXT:    br i1 [[C_2]], label %[[LOOP_2_PREHEADER:.*]], label %[[LOOP_0_LATCH:.*]]
 ; CHECK:       [[LOOP_2_PREHEADER]]:
-; CHECK-NEXT:    [[IV_1_LCSSA_LCSSA:%.*]] = phi ptr [ [[IV_1_LCSSA]], %[[THEN]] ]
+; CHECK-NEXT:    [[IV_1_LCSSA:%.*]] = phi ptr [ [[IV_1_LCSSA1]], %[[THEN]] ]
+; CHECK-NEXT:    [[IV_1_LCSSA_LCSSA:%.*]] = phi ptr [ [[IV_1_LCSSA1]], %[[THEN]] ]
 ; CHECK-NEXT:    [[STRLEN:%.*]] = call i64 @strlen(ptr null)
 ; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr i8, ptr [[IV_1_LCSSA]], i64 1
 ; CHECK-NEXT:    [[SCEVGEP:%.*]] = getelementptr i8, ptr [[TMP0]], i64 [[STRLEN]]

llvm/test/Transforms/LoopUnroll/Hexagon/reuse-lcssa-phi-scev-expansion.ll

@@ -0,0 +1,108 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -p loop-unroll -S %s | FileCheck %s
+
+target triple = "hexagon-unknown-linux"
+
+declare void @foo()
+
+define void @preserve_lcssa_when_reusing_existing_phi() {
+; CHECK-LABEL: define void @preserve_lcssa_when_reusing_existing_phi() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[LOOP_1_HEADER:.*]]
+; CHECK:       [[LOOP_1_HEADER]]:
+; CHECK-NEXT:    br label %[[LOOP_2_HEADER:.*]]
+; CHECK:       [[LOOP_2_HEADER]]:
+; CHECK-NEXT:    br label %[[LOOP_3:.*]]
+; CHECK:       [[LOOP_3]]:
+; CHECK-NEXT:    [[IV_3:%.*]] = phi i32 [ [[IV_3_NEXT:%.*]], %[[LOOP_3]] ], [ 0, %[[LOOP_2_HEADER]] ]
+; CHECK-NEXT:    call void @foo()
+; CHECK-NEXT:    [[IV_3_NEXT]] = add i32 [[IV_3]], 1
+; CHECK-NEXT:    br i1 false, label %[[PH:.*]], label %[[LOOP_3]]
+; CHECK:       [[PH]]:
+; CHECK-NEXT:    [[IV_3_LCSSA:%.*]] = phi i32 [ [[IV_3]], %[[LOOP_3]] ]
+; CHECK-NEXT:    br i1 true, label %[[LOOP_2_LATCH:.*]], label %[[LOOP_4_PREHEADER:.*]]
+; CHECK:       [[LOOP_4_PREHEADER]]:
+; CHECK-NEXT:    [[IV_3_LCSSA_LCSSA1:%.*]] = phi i32 [ [[IV_3_LCSSA]], %[[PH]] ]
+; CHECK-NEXT:    [[IV_3_LCSSA_LCSSA:%.*]] = phi i32 [ [[IV_3_LCSSA]], %[[PH]] ]
+; CHECK-NEXT:    [[TMP0:%.*]] = add i32 [[IV_3_LCSSA_LCSSA1]], 1
+; CHECK-NEXT:    [[TMP1:%.*]] = freeze i32 [[TMP0]]
+; CHECK-NEXT:    [[TMP2:%.*]] = add i32 [[TMP1]], -1
+; CHECK-NEXT:    [[XTRAITER:%.*]] = and i32 [[TMP1]], 7
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ult i32 [[TMP2]], 7
+; CHECK-NEXT:    br i1 [[TMP3]], label %[[LOOP_1_LATCH_UNR_LCSSA:.*]], label %[[LOOP_4_PREHEADER_NEW:.*]]
+; CHECK:       [[LOOP_4_PREHEADER_NEW]]:
+; CHECK-NEXT:    br label %[[LOOP_4:.*]]
+; CHECK:       [[LOOP_2_LATCH]]:
+; CHECK-NEXT:    br label %[[LOOP_2_HEADER]]
+; CHECK:       [[LOOP_4]]:
+; CHECK-NEXT:    [[IV_4:%.*]] = phi i32 [ 0, %[[LOOP_4_PREHEADER_NEW]] ], [ [[INC_I_7:%.*]], %[[LOOP_4]] ]
+; CHECK-NEXT:    [[NITER:%.*]] = phi i32 [ 0, %[[LOOP_4_PREHEADER_NEW]] ], [ [[NITER_NEXT_7:%.*]], %[[LOOP_4]] ]
+; CHECK-NEXT:    call void @foo()
+; CHECK-NEXT:    call void @foo()
+; CHECK-NEXT:    call void @foo()
+; CHECK-NEXT:    call void @foo()
+; CHECK-NEXT:    call void @foo()
+; CHECK-NEXT:    call void @foo()
+; CHECK-NEXT:    call void @foo()
+; CHECK-NEXT:    call void @foo()
+; CHECK-NEXT:    [[INC_I_7]] = add nuw nsw i32 [[IV_4]], 8
+; CHECK-NEXT:    [[NITER_NEXT_7]] = add nuw nsw i32 [[NITER]], 8
+; CHECK-NEXT:    br i1 true, label %[[LOOP_1_LATCH_UNR_LCSSA_LOOPEXIT:.*]], label %[[LOOP_4]]
+; CHECK:       [[LOOP_1_LATCH_UNR_LCSSA_LOOPEXIT]]:
+; CHECK-NEXT:    [[IV_4_UNR_PH:%.*]] = phi i32 [ [[INC_I_7]], %[[LOOP_4]] ]
+; CHECK-NEXT:    br label %[[LOOP_1_LATCH_UNR_LCSSA]]
+; CHECK:       [[LOOP_1_LATCH_UNR_LCSSA]]:
+; CHECK-NEXT:    [[IV_4_UNR:%.*]] = phi i32 [ 0, %[[LOOP_4_PREHEADER]] ], [ [[IV_4_UNR_PH]], %[[LOOP_1_LATCH_UNR_LCSSA_LOOPEXIT]] ]
+; CHECK-NEXT:    [[LCMP_MOD:%.*]] = icmp ne i32 [[XTRAITER]], 0
+; CHECK-NEXT:    br i1 [[LCMP_MOD]], label %[[LOOP_4_EPIL_PREHEADER:.*]], label %[[LOOP_1_LATCH:.*]]
+; CHECK:       [[LOOP_4_EPIL_PREHEADER]]:
+; CHECK-NEXT:    br label %[[LOOP_4_EPIL:.*]]
+; CHECK:       [[LOOP_4_EPIL]]:
+; CHECK-NEXT:    [[IV_4_EPIL:%.*]] = phi i32 [ [[INC_I_EPIL:%.*]], %[[LOOP_4_EPIL]] ], [ [[IV_4_UNR]], %[[LOOP_4_EPIL_PREHEADER]] ]
+; CHECK-NEXT:    [[EPIL_ITER:%.*]] = phi i32 [ 0, %[[LOOP_4_EPIL_PREHEADER]] ], [ [[EPIL_ITER_NEXT:%.*]], %[[LOOP_4_EPIL]] ]
+; CHECK-NEXT:    call void @foo()
+; CHECK-NEXT:    [[INC_I_EPIL]] = add i32 [[IV_4_EPIL]], 1
+; CHECK-NEXT:    [[EC_EPIL:%.*]] = icmp eq i32 [[IV_4_EPIL]], [[IV_3_LCSSA_LCSSA]]
+; CHECK-NEXT:    [[EPIL_ITER_NEXT]] = add i32 [[EPIL_ITER]], 1
+; CHECK-NEXT:    [[EPIL_ITER_CMP:%.*]] = icmp ne i32 [[EPIL_ITER_NEXT]], [[XTRAITER]]
+; CHECK-NEXT:    br i1 [[EPIL_ITER_CMP]], label %[[LOOP_4_EPIL]], label %[[LOOP_1_LATCH_EPILOG_LCSSA:.*]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK:       [[LOOP_1_LATCH_EPILOG_LCSSA]]:
+; CHECK-NEXT:    br label %[[LOOP_1_LATCH]]
+; CHECK:       [[LOOP_1_LATCH]]:
+; CHECK-NEXT:    br label %[[LOOP_1_HEADER]]
+;
+entry:
+  br label %loop.1.header
+
+loop.1.header:
+  br label %loop.2.header
+
+loop.2.header:
+  br label %loop.3
+
+loop.3:
+  %iv.3 = phi i32 [ %iv.3.next, %loop.3 ], [ 0, %loop.2.header ]
+  call void @foo()
+  %iv.3.next = add i32 %iv.3, 1
+  br i1 false, label %ph, label %loop.3
+
+ph:
+  br i1 true, label %loop.2.latch, label %loop.4
+
+loop.2.latch:
+  br label %loop.2.header
+
+loop.4:
+  %iv.4 = phi i32 [ 0, %ph ], [ %inc.i, %loop.4 ]
+  call void @foo()
+  %inc.i = add i32 %iv.4, 1
+  %ec = icmp eq i32 %iv.4, %iv.3
+  br i1 %ec, label %loop.1.latch, label %loop.4
+
+loop.1.latch:
+  br label %loop.1.header
+}
+;.
+; CHECK: [[LOOP0]] = distinct !{[[LOOP0]], [[META1:![0-9]+]]}
+; CHECK: [[META1]] = !{!"llvm.loop.unroll.disable"}
+;.