[llvm] r217115 - IndVarSimplify: Address review comments for r217102

David Majnemer david.majnemer at gmail.com
Wed Sep 3 17:23:13 PDT 2014

Author: majnemer
Date: Wed Sep  3 19:23:13 2014
New Revision: 217115

URL: http://llvm.org/viewvc/llvm-project?rev=217115&view=rev
IndVarSimplify: Address review comments for r217102

No functional change intended, just some cleanups and comments added.


Modified: llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp?rev=217115&r1=217114&r2=217115&view=diff
--- llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp Wed Sep  3 19:23:13 2014
@@ -1644,16 +1644,19 @@ LinearFunctionTestReplace(Loop *L,
     // The BackedgeTaken expression contains the number of times that the
     // backedge branches to the loop header.  This is one less than the
     // number of times the loop executes, so use the incremented indvar.
-    llvm::Value *IncrementedIndvar = IndVar->getIncomingValueForBlock(L->getExitingBlock());
+    llvm::Value *IncrementedIndvar =
+        IndVar->getIncomingValueForBlock(L->getExitingBlock());
     const auto *IncrementedIndvarSCEV =
     // It is unsafe to use the incremented indvar if it has a wrapping flag, we
     // don't want to compare against a poison value.  Check the SCEV that
     // corresponds to the incremented indvar, the SCEVExpander will only insert
     // flags in the IR if the SCEV originally had wrapping flags.
-    if (ScalarEvolution::maskFlags(IncrementedIndvarSCEV->getNoWrapFlags(),
-                                   SCEV::FlagNUW | SCEV::FlagNSW) ==
-        SCEV::FlagAnyWrap) {
+    // FIXME: In theory, SCEV could drop flags even though they exist in IR.
+    // A more robust solution would involve getting a new expression for
+    // CmpIndVar by applying non-NSW/NUW AddExprs.
+    if (!ScalarEvolution::maskFlags(IncrementedIndvarSCEV->getNoWrapFlags(),
+                                    SCEV::FlagNUW | SCEV::FlagNSW)) {
       // Add one to the "backedge-taken" count to get the trip count.
       // This addition may overflow, which is valid as long as the comparison is
       // truncated to BackedgeTakenCount->getType().

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