[PATCH] D47951: [SCEV] Look through zero-extends in howFarToZero

[Krzysztof Parzyszek via Phabricator via llvm-commits]

kparzysz created this revision.
kparzysz added reviewers: sanjoy, eli.friedman.

An expression like `(zext i2 {(trunc i32 (1 + %B) to i2),+,1}<%while.body> to i32)` will become zero exactly when the nested value becomes zero in its type. Instead of converting this kind of a zero-extended value into an addrec with predicates, simply remove the zext.

This is the replacement of https://reviews.llvm.org/D47899 (the motivation is explained there).


Repository:
  rL LLVM

https://reviews.llvm.org/D47951

Files:
  lib/Analysis/ScalarEvolution.cpp


Index: lib/Analysis/ScalarEvolution.cpp
===================================================================
--- lib/Analysis/ScalarEvolution.cpp
+++ lib/Analysis/ScalarEvolution.cpp
@@ -8265,7 +8265,6 @@
 ScalarEvolution::ExitLimit
 ScalarEvolution::howFarToZero(const SCEV *V, const Loop *L, bool ControlsExit,
                               bool AllowPredicates) {
-
   // This is only used for loops with a "x != y" exit test. The exit condition
   // is now expressed as a single expression, V = x-y. So the exit test is
   // effectively V != 0.  We know and take advantage of the fact that this
@@ -8280,6 +8279,12 @@
   }
 
   const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(V);
+  if (!AddRec) {
+    if (const SCEVZeroExtendExpr *Z = dyn_cast<SCEVZeroExtendExpr>(V))
+      if (const SCEVAddRecExpr *A = dyn_cast<SCEVAddRecExpr>(Z->getOperand()))
+        AddRec = A;
+  }
+
   if (!AddRec && AllowPredicates)
     // Try to make this an AddRec using runtime tests, in the first X
     // iterations of this loop, where X is the SCEV expression found by the


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