[PATCH] D72807: [InstCombine] Fix worklist management in DSE (PR44552)

[Nikita Popov via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rG522c030aa9b1: [InstCombine] Fix worklist management in DSE (PR44552) (authored by nikic).

Changed prior to commit:
  https://reviews.llvm.org/D72807?vs=238362&id=238800#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D72807/new/

https://reviews.llvm.org/D72807

Files:
  llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
  llvm/test/Transforms/InstCombine/pr44552.ll


Index: llvm/test/Transforms/InstCombine/pr44552.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/InstCombine/pr44552.ll
@@ -0,0 +1,59 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -instcombine -instcombine-infinite-loop-threshold=2 < %s | FileCheck %s
+
+; This used to require 10 instcombine iterations to fully optimize.
+; The number of iterations grew linearly with the number of DSEd stores,
+; resulting in overall quadratic runtime.
+
+%struct.S3 = type { i64 }
+
+ at csmith_sink_ = dso_local global i64 0, align 1
+ at g_302_7 = internal constant i32 0, align 1
+ at g_313_0 = internal global i16 0, align 1
+ at g_313_1 = internal global i32 0, align 1
+ at g_313_2 = internal global i32 0, align 1
+ at g_313_3 = internal global i32 0, align 1
+ at g_313_4 = internal global i16 0, align 1
+ at g_313_5 = internal global i16 0, align 1
+ at g_313_6 = internal global i16 0, align 1
+ at g_316 = internal global %struct.S3 zeroinitializer, align 1
+ at g_316_1_0 = internal global i16 0, align 1
+
+define i16 @main() {
+; CHECK-LABEL: @main(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    store i64 0, i64* @csmith_sink_, align 8
+; CHECK-NEXT:    ret i16 0
+;
+entry:
+  store i64 0, i64* @csmith_sink_, align 1
+  %0 = load i16, i16* @g_313_0, align 1
+  %conv2 = sext i16 %0 to i64
+  store i64 %conv2, i64* @csmith_sink_, align 1
+  %1 = load i32, i32* @g_313_1, align 1
+  %conv3 = zext i32 %1 to i64
+  store i64 %conv3, i64* @csmith_sink_, align 1
+  %2 = load i32, i32* @g_313_2, align 1
+  %conv4 = sext i32 %2 to i64
+  store i64 %conv4, i64* @csmith_sink_, align 1
+  %3 = load i32, i32* @g_313_3, align 1
+  %conv5 = zext i32 %3 to i64
+  store i64 %conv5, i64* @csmith_sink_, align 1
+  %4 = load i16, i16* @g_313_4, align 1
+  %conv6 = sext i16 %4 to i64
+  store i64 %conv6, i64* @csmith_sink_, align 1
+  %5 = load i16, i16* @g_313_5, align 1
+  %conv7 = sext i16 %5 to i64
+  store i64 %conv7, i64* @csmith_sink_, align 1
+  %6 = load i16, i16* @g_313_6, align 1
+  %conv8 = sext i16 %6 to i64
+  store i64 %conv8, i64* @csmith_sink_, align 1
+  %7 = load i64, i64* getelementptr inbounds (%struct.S3, %struct.S3* @g_316, i32 0, i32 0), align 1
+  store i64 %7, i64* @csmith_sink_, align 1
+  %8 = load i16, i16* @g_316_1_0, align 1
+  %conv9 = sext i16 %8 to i64
+  store i64 %conv9, i64* @csmith_sink_, align 1
+  store i64 0, i64* @csmith_sink_, align 1
+  ret i16 0
+}
+
Index: llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -1439,9 +1439,12 @@
       if (PrevSI->isUnordered() && equivalentAddressValues(PrevSI->getOperand(1),
                                                         SI.getOperand(1))) {
         ++NumDeadStore;
-        ++BBI;
+        // Manually add back the original store to the worklist now, so it will
+        // be processed after the operands of the removed store, as this may
+        // expose additional DSE opportunities.
+        Worklist.Add(&SI);
         eraseInstFromFunction(*PrevSI);
-        continue;
+        return nullptr;
       }
       break;
     }


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