[llvm-branch-commits] [llvm-branch] r311603 - Merging r311554:

[Hans Wennborg via llvm-branch-commits]

Author: hans
Date: Wed Aug 23 14:33:38 2017
New Revision: 311603

URL: http://llvm.org/viewvc/llvm-project?rev=311603&view=rev
Log:
Merging r311554:
------------------------------------------------------------------------
r311554 | mcrosier | 2017-08-23 07:10:06 -0700 (Wed, 23 Aug 2017) | 10 lines

[Reassociate] Don't canonicalize x + (-Constant * y) -> x - (Constant * y)..

..if the resulting subtract will be broken up later.  This can cause us to get
into an infinite loop.

x + (-5.0 * y)      -> x - (5.0 * y)       ; Canonicalize neg const
x - (5.0 * y)       -> x + (0 - (5.0 * y)) ; Break up subtract
x + (0 - (5.0 * y)) -> x + (-5.0 * y)      ; Replace 0-X with X*-1.

PR34078
------------------------------------------------------------------------

Modified:
    llvm/branches/release_50/   (props changed)
    llvm/branches/release_50/lib/Transforms/Scalar/Reassociate.cpp
    llvm/branches/release_50/test/Transforms/Reassociate/canonicalize-neg-const.ll

Propchange: llvm/branches/release_50/
------------------------------------------------------------------------------
--- svn:mergeinfo (original)
+++ svn:mergeinfo Wed Aug 23 14:33:38 2017
@@ -1,3 +1,3 @@
 /llvm/branches/Apple/Pertwee:110850,110961
 /llvm/branches/type-system-rewrite:133420-134817
-/llvm/trunk:155241,308483-308484,308503,308808,308813,308847,308891,308906,308950,308963,308978,308986,309044,309071,309113,309120,309122,309140,309227,309302,309321,309323,309325,309330,309343,309353,309355,309422,309481,309483,309495,309555,309561,309594,309614,309651,309744,309758,309849,309928,309930,309945,310066,310071,310190,310240-310242,310250,310253,310262,310267,310481,310492,310498,310510,310534,310552,310604,310712,310779,310784,310796,310842,310906,310926,310939,310979,310988,310990-310991,311061,311068,311071,311087,311229,311258,311263,311387,311429,311565,311572
+/llvm/trunk:155241,308483-308484,308503,308808,308813,308847,308891,308906,308950,308963,308978,308986,309044,309071,309113,309120,309122,309140,309227,309302,309321,309323,309325,309330,309343,309353,309355,309422,309481,309483,309495,309555,309561,309594,309614,309651,309744,309758,309849,309928,309930,309945,310066,310071,310190,310240-310242,310250,310253,310262,310267,310481,310492,310498,310510,310534,310552,310604,310712,310779,310784,310796,310842,310906,310926,310939,310979,310988,310990-310991,311061,311068,311071,311087,311229,311258,311263,311387,311429,311554,311565,311572

Modified: llvm/branches/release_50/lib/Transforms/Scalar/Reassociate.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/branches/release_50/lib/Transforms/Scalar/Reassociate.cpp?rev=311603&r1=311602&r2=311603&view=diff
==============================================================================
--- llvm/branches/release_50/lib/Transforms/Scalar/Reassociate.cpp (original)
+++ llvm/branches/release_50/lib/Transforms/Scalar/Reassociate.cpp Wed Aug 23 14:33:38 2017
@@ -1941,6 +1941,12 @@ Instruction *ReassociatePass::canonicali
   if (!User->isCommutative() && User->getOperand(1) != I)
     return nullptr;
 
+  // Don't canonicalize x + (-Constant * y) -> x - (Constant * y), if the
+  // resulting subtract will be broken up later.  This can get us into an
+  // infinite loop during reassociation.
+  if (UserOpcode == Instruction::FAdd && ShouldBreakUpSubtract(User))
+    return nullptr;
+
   // Change the sign of the constant.
   APFloat Val = CF->getValueAPF();
   Val.changeSign();

Modified: llvm/branches/release_50/test/Transforms/Reassociate/canonicalize-neg-const.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/branches/release_50/test/Transforms/Reassociate/canonicalize-neg-const.ll?rev=311603&r1=311602&r2=311603&view=diff
==============================================================================
--- llvm/branches/release_50/test/Transforms/Reassociate/canonicalize-neg-const.ll (original)
+++ llvm/branches/release_50/test/Transforms/Reassociate/canonicalize-neg-const.ll Wed Aug 23 14:33:38 2017
@@ -154,3 +154,25 @@ define i4 @test13(i4 %x) {
   %add = add i4 %mul, 3
   ret i4 %add
 }
+
+; This tests used to cause an infinite loop where we would loop between
+; canonicalizing the negated constant (i.e., (X + Y*-5.0) -> (X - Y*5.0)) and
+; breaking up a subtract (i.e., (X - Y*5.0) -> X + (0 - Y*5.0)). To break the
+; cycle, we don't canonicalize the negative constant if we're going to later
+; break up the subtract.
+;
+; Check to make sure we don't canonicalize
+;   (%pow2*-5.0 + %sub) -> (%sub - %pow2*5.0)
+; as we would later break up this subtract causing a cycle.
+;
+; CHECK-LABEL: @pr34078
+; CHECK: %mul5.neg = fmul fast double %pow2, -5.000000e-01
+; CHECK: %sub1 = fadd fast double %mul5.neg, %sub
+define double @pr34078(double %A) {
+  %sub = fsub fast double 1.000000e+00, %A
+  %pow2 = fmul double %A, %A
+  %mul5 = fmul fast double %pow2, 5.000000e-01
+  %sub1 = fsub fast double %sub, %mul5
+  %add = fadd fast double %sub1, %sub1
+  ret double %add
+}