[PATCH] D155255: [SCEV] Don't update the range value if empty

[Davide Italiano via Phabricator via llvm-commits]

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The recent commit 22ca38da25e19a7c5fcfeb3f22159aba92ec381e <https://reviews.llvm.org/rG22ca38da25e19a7c5fcfeb3f22159aba92ec381e> introduces the ability to analyze ranges for heap allocations.

In some cases, like the one in the test, the range is empty as `ConstantRange` represents an half-open range on the upper side (in the very specific case, [1;1)). Detect this case, similarly to other ranges transformations in SCEV, rather than crashing.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D155255

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Transforms/LoopStrengthReduce/scev-operator-new.ll


Index: llvm/test/Transforms/LoopStrengthReduce/scev-operator-new.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/LoopStrengthReduce/scev-operator-new.ll
@@ -0,0 +1,24 @@
+; RUN: opt < %s -passes=loop-reduce -S | FileCheck %s
+
+; CHECK: define void @patatino() {
+; CHECK-NEXT: entry:
+; CHECK-NEXT:  br label %for.cond9
+
+; CHECK: for.cond9:
+; CHECK-NEXT:  br label %for.cond9
+; CHECK-NEXT:}
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @patatino() {
+entry:
+  %call443 = tail call nonnull ptr @_Znam(i64 -1)
+  br label %for.cond9
+
+for.cond9:
+  %lsr.iv = phi ptr [ %call443, %entry ], [ %scevgep, %for.cond9 ]
+  %scevgep = getelementptr i8, ptr %lsr.iv, i64 4
+  br label %for.cond9
+}
+
+declare ptr @_Znam(i64)
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -6832,8 +6832,10 @@
         APInt MinVal = APInt::getZero(BitWidth);
         if (llvm::isKnownNonZero(V, DL))
           MinVal = Align;
-        ConservativeResult = ConservativeResult.intersectWith(
-            {MinVal, MaxVal + 1}, RangeType);
+        if (MinVal != MaxVal + 1) {
+          ConservativeResult = ConservativeResult.intersectWith(
+              {MinVal, MaxVal + 1}, RangeType);
+        }
       }
     }
 


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