[PATCH] D140836: Do not short circuit hoistIVInc when recomputation of poison flags is needed.

[Owen Anderson via Phabricator via llvm-commits]

resistor updated this revision to Diff 486151.
resistor added a comment.

Extract poison fixup logic to a helper and apply it in the short-circuit case without 
going through the rest of the hoisting process.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D140836/new/

https://reviews.llvm.org/D140836

Files:
  llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
  llvm/test/Transforms/IndVarSimplify/iv-poison.ll


Index: llvm/test/Transforms/IndVarSimplify/iv-poison.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/IndVarSimplify/iv-poison.ll
@@ -0,0 +1,28 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=indvars -S < %s | FileCheck %s
+
+define i2 @iv_hoist_nsw_poison(i2 %0) {
+; CHECK-LABEL: @iv_hoist_nsw_poison(
+; CHECK-NEXT:    br label [[TMP2:%.*]]
+; CHECK:       2:
+; CHECK-NEXT:    [[DOT07:%.*]] = phi i2 [ 1, [[TMP1:%.*]] ], [ [[TMP3:%.*]], [[TMP2]] ]
+; CHECK-NEXT:    [[TMP3]] = add nuw i2 [[DOT07]], 1
+; CHECK-NEXT:    [[DOTNOT_NOT:%.*]] = icmp ult i2 1, [[TMP0:%.*]]
+; CHECK-NEXT:    br i1 [[DOTNOT_NOT]], label [[COMMON_RET:%.*]], label [[TMP2]]
+; CHECK:       common.ret:
+; CHECK-NEXT:    [[DOTLCSSA:%.*]] = phi i2 [ [[TMP3]], [[TMP2]] ]
+; CHECK-NEXT:    ret i2 [[DOTLCSSA]]
+;
+  br label %2
+
+2:                                                ; preds = %2, %1
+  %.07 = phi i2 [ 1, %1 ], [ %3, %2 ]
+  %.0 = phi i2 [ 1, %1 ], [ %4, %2 ]
+  %3 = add nsw i2 %.07, 1
+  %4 = add i2 %.0, 1
+  %.not.not = icmp ult i2 %.07, %0
+  br i1 %.not.not, label %common.ret, label %2
+
+common.ret:                                       ; preds = %2
+  ret i2 %4
+}
Index: llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
===================================================================
--- llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -1026,8 +1026,24 @@
 /// until we reach a value that dominates InsertPos.
 bool SCEVExpander::hoistIVInc(Instruction *IncV, Instruction *InsertPos,
                               bool RecomputePoisonFlags) {
-  if (SE.DT.dominates(IncV, InsertPos))
-      return true;
+  auto FixupPoisonFlags = [this](Instruction *I) {
+    // Drop flags that are potentially inferred from old context and infer flags
+    // in new context.
+    I->dropPoisonGeneratingFlags();
+    if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(I))
+      if (auto Flags = SE.getStrengthenedNoWrapFlagsFromBinOp(OBO)) {
+        auto *BO = cast<BinaryOperator>(I);
+        BO->setHasNoUnsignedWrap(
+            ScalarEvolution::maskFlags(*Flags, SCEV::FlagNUW) == SCEV::FlagNUW);
+        BO->setHasNoSignedWrap(
+            ScalarEvolution::maskFlags(*Flags, SCEV::FlagNSW) == SCEV::FlagNSW);
+      }
+  };
+
+  if (SE.DT.dominates(IncV, InsertPos)) {
+    if (RecomputePoisonFlags) FixupPoisonFlags(IncV);
+    return true;
+  }
 
   // InsertPos must itself dominate IncV so that IncV's new position satisfies
   // its existing users.
@@ -1053,19 +1069,7 @@
   for (Instruction *I : llvm::reverse(IVIncs)) {
     fixupInsertPoints(I);
     I->moveBefore(InsertPos);
-    if (!RecomputePoisonFlags)
-      continue;
-    // Drop flags that are potentially inferred from old context and infer flags
-    // in new context.
-    I->dropPoisonGeneratingFlags();
-    if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(I))
-      if (auto Flags = SE.getStrengthenedNoWrapFlagsFromBinOp(OBO)) {
-        auto *BO = cast<BinaryOperator>(I);
-        BO->setHasNoUnsignedWrap(
-            ScalarEvolution::maskFlags(*Flags, SCEV::FlagNUW) == SCEV::FlagNUW);
-        BO->setHasNoSignedWrap(
-            ScalarEvolution::maskFlags(*Flags, SCEV::FlagNSW) == SCEV::FlagNSW);
-      }
+    if (RecomputePoisonFlags) FixupPoisonFlags(I);
   }
   return true;
 }


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