[llvm-branch-commits] [llvm-branch] r310629 - Merging r308847:

[Hans Wennborg via llvm-branch-commits]

Author: hans
Date: Thu Aug 10 10:15:06 2017
New Revision: 310629

URL: http://llvm.org/viewvc/llvm-project?rev=310629&view=rev
Log:
Merging r308847:
------------------------------------------------------------------------
r308847 | mkazantsev | 2017-07-23 08:40:19 -0700 (Sun, 23 Jul 2017) | 24 lines

[SCEV] Limit max size of AddRecExpr during evolving

When SCEV calculates product of two SCEVAddRecs from the same loop, it
tries to combine them into one big AddRecExpr. If the sizes of the initial
SCEVs were `S1` and `S2`, the size of their product is `S1 + S2 - 1`, and every
operand of the resulting SCEV is combined from operands of initial SCEV and
has much higher complexity than they have.

As result, if we try to calculate something like:
  %x1 = {a,+,b}
  %x2 = mul i32 %x1, %x1
  %x3 = mul i32 %x2, %x1
  %x4 = mul i32 %x3, %x2
  ...
The size of such SCEVs grows as `2^N`, and the arguments
become more and more complex as we go forth. This leads
to long compilation and huge memory consumption.

This patch sets a limit after which we don't try to combine two
`SCEVAddRecExpr`s into one. By default, max allowed size of the
resulting AddRecExpr is set to 16.

Differential Revision: https://reviews.llvm.org/D35664

------------------------------------------------------------------------

Added:
    llvm/branches/release_50/test/Analysis/ScalarEvolution/max-addrec-size.ll
      - copied unchanged from r308847, llvm/trunk/test/Analysis/ScalarEvolution/max-addrec-size.ll
Modified:
    llvm/branches/release_50/   (props changed)
    llvm/branches/release_50/lib/Analysis/ScalarEvolution.cpp

Propchange: llvm/branches/release_50/
------------------------------------------------------------------------------
--- svn:mergeinfo (original)
+++ svn:mergeinfo Thu Aug 10 10:15:06 2017
@@ -1,3 +1,3 @@
 /llvm/branches/Apple/Pertwee:110850,110961
 /llvm/branches/type-system-rewrite:133420-134817
-/llvm/trunk:155241,308483-308484,308503,308808,308813,308891,308906,308950,308963,308978,308986,309113,309302,309321,309323,309325,309330,309343,309353,309355,309422,309481,309483,309495,309555,309561,309594,309651,309744,309758,309849,309928,309930,310071,310190,310240-310242,310250,310253,310267,310534
+/llvm/trunk:155241,308483-308484,308503,308808,308813,308847,308891,308906,308950,308963,308978,308986,309113,309302,309321,309323,309325,309330,309343,309353,309355,309422,309481,309483,309495,309555,309561,309594,309651,309744,309758,309849,309928,309930,310071,310190,310240-310242,310250,310253,310267,310534

Modified: llvm/branches/release_50/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/branches/release_50/lib/Analysis/ScalarEvolution.cpp?rev=310629&r1=310628&r2=310629&view=diff
==============================================================================
--- llvm/branches/release_50/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/branches/release_50/lib/Analysis/ScalarEvolution.cpp Thu Aug 10 10:15:06 2017
@@ -162,6 +162,11 @@ static cl::opt<unsigned>
                 cl::desc("Maximum depth of recursive SExt/ZExt"),
                 cl::init(8));
 
+static cl::opt<unsigned>
+    MaxAddRecSize("scalar-evolution-max-add-rec-size", cl::Hidden,
+                  cl::desc("Max coefficients in AddRec during evolving"),
+                  cl::init(16));
+
 //===----------------------------------------------------------------------===//
 //                           SCEV class definitions
 //===----------------------------------------------------------------------===//
@@ -2878,6 +2883,12 @@ const SCEV *ScalarEvolution::getMulExpr(
       if (!OtherAddRec || OtherAddRec->getLoop() != AddRecLoop)
         continue;
 
+      // Limit max number of arguments to avoid creation of unreasonably big
+      // SCEVAddRecs with very complex operands.
+      if (AddRec->getNumOperands() + OtherAddRec->getNumOperands() - 1 >
+          MaxAddRecSize)
+        continue;
+
       bool Overflow = false;
       Type *Ty = AddRec->getType();
       bool LargerThan64Bits = getTypeSizeInBits(Ty) > 64;