[llvm-branch-commits] [llvm] release/19.x: [IndVars] Check if WideInc available before trying to use it (PR #106892)

[via llvm-branch-commits]

https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/106892

Backport c9a5e1b665dbba898e9981fd7d48881947e6560e

Requested by: @nikic

>From cf74f4b3c57683edd22f2383f62f056eeeba98ca Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Wed, 28 Aug 2024 12:54:14 +0200
Subject: [PATCH] [IndVars] Check if WideInc available before trying to use it

WideInc/WideIncExpr can be null. Previously this worked out
because the comparison with WideIncExpr would fail. Now we have
accesses to WideInc prior to that. Avoid the issue with an
explicit check.

Fixes https://github.com/llvm/llvm-project/issues/106239.

(cherry picked from commit c9a5e1b665dbba898e9981fd7d48881947e6560e)
---
 llvm/lib/Transforms/Utils/SimplifyIndVar.cpp  | 28 +++++++++------
 .../Transforms/IndVarSimplify/pr106239.ll     | 36 +++++++++++++++++++
 2 files changed, 53 insertions(+), 11 deletions(-)
 create mode 100644 llvm/test/Transforms/IndVarSimplify/pr106239.ll

diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index 5bda7c50c62c66..0b4a75e0bc52de 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -1928,18 +1928,24 @@ Instruction *WidenIV::widenIVUse(WidenIV::NarrowIVDefUse DU,
     if (!WideAddRec.first)
       return nullptr;
 
-    // Reuse the IV increment that SCEVExpander created. Recompute flags, unless
-    // the flags for both increments agree and it is safe to use the ones from
-    // the original inc. In that case, the new use of the wide increment won't
-    // be more poisonous.
-    bool NeedToRecomputeFlags =
-        !SCEVExpander::canReuseFlagsFromOriginalIVInc(OrigPhi, WidePhi,
-                                                      DU.NarrowUse, WideInc) ||
-        DU.NarrowUse->hasNoUnsignedWrap() != WideInc->hasNoUnsignedWrap() ||
-        DU.NarrowUse->hasNoSignedWrap() != WideInc->hasNoSignedWrap();
+    auto CanUseWideInc = [&]() {
+      if (!WideInc)
+        return false;
+      // Reuse the IV increment that SCEVExpander created. Recompute flags,
+      // unless the flags for both increments agree and it is safe to use the
+      // ones from the original inc. In that case, the new use of the wide
+      // increment won't be more poisonous.
+      bool NeedToRecomputeFlags =
+          !SCEVExpander::canReuseFlagsFromOriginalIVInc(
+              OrigPhi, WidePhi, DU.NarrowUse, WideInc) ||
+          DU.NarrowUse->hasNoUnsignedWrap() != WideInc->hasNoUnsignedWrap() ||
+          DU.NarrowUse->hasNoSignedWrap() != WideInc->hasNoSignedWrap();
+      return WideAddRec.first == WideIncExpr &&
+             Rewriter.hoistIVInc(WideInc, DU.NarrowUse, NeedToRecomputeFlags);
+    };
+
     Instruction *WideUse = nullptr;
-    if (WideAddRec.first == WideIncExpr &&
-        Rewriter.hoistIVInc(WideInc, DU.NarrowUse, NeedToRecomputeFlags))
+    if (CanUseWideInc())
       WideUse = WideInc;
     else {
       WideUse = cloneIVUser(DU, WideAddRec.first);
diff --git a/llvm/test/Transforms/IndVarSimplify/pr106239.ll b/llvm/test/Transforms/IndVarSimplify/pr106239.ll
new file mode 100644
index 00000000000000..8d5aa99539a5a7
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/pr106239.ll
@@ -0,0 +1,36 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=indvars < %s | FileCheck %s
+
+target datalayout = "n8:16:32:64"
+
+; Make sure it does not crash.
+
+define i32 @m() {
+; CHECK-LABEL: define i32 @m() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[FOR_BODY_I6:.*]]
+; CHECK:       [[FOR_BODY_I6]]:
+; CHECK-NEXT:    br i1 true, label %[[I_EXIT:.*]], label %[[IF_END_I:.*]]
+; CHECK:       [[IF_END_I]]:
+; CHECK-NEXT:    store i64 0, ptr null, align 8
+; CHECK-NEXT:    br label %[[FOR_BODY_I6]]
+; CHECK:       [[I_EXIT]]:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %div.i4 = sdiv i32 1, 0
+  br label %for.body.i6
+
+for.body.i6:                                      ; preds = %if.end.i, %entry
+  %add57.i = phi i32 [ %add.i7, %if.end.i ], [ 0, %entry ]
+  br i1 true, label %i.exit, label %if.end.i
+
+if.end.i:                                         ; preds = %for.body.i6
+  %add.i7 = add i32 %add57.i, %div.i4
+  %conv.i = zext i32 %add57.i to i64
+  store i64 %conv.i, ptr null, align 8
+  br label %for.body.i6
+
+i.exit:                                           ; preds = %for.body.i6
+  ret i32 0
+}