[llvm] r269212 - [SCEVExpander] Don't break SSA in replaceCongruentIVs

[Sanjoy Das via llvm-commits]

Author: sanjoy
Date: Wed May 11 12:41:34 2016
New Revision: 269212

URL: http://llvm.org/viewvc/llvm-project?rev=269212&view=rev
Log:
[SCEVExpander] Don't break SSA in replaceCongruentIVs

`SCEVExpander::replaceCongruentIVs` bypasses `hoistIVInc` if both the
original and the isomorphic increments are PHI nodes.  Doing this can
break SSA if the isomorphic increment is not dominated by the original
increment.  Get rid of the bypass, and let `hoistIVInc` do the right
thing.

Fixes PR27232 (compile time crash/hang).

Added:
    llvm/trunk/test/Analysis/ScalarEvolution/expander-replace-congruent-ivs.ll
Modified:
    llvm/trunk/lib/Analysis/ScalarEvolutionExpander.cpp

Modified: llvm/trunk/lib/Analysis/ScalarEvolutionExpander.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolutionExpander.cpp?rev=269212&r1=269211&r2=269212&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolutionExpander.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolutionExpander.cpp Wed May 11 12:41:34 2016
@@ -1820,8 +1820,7 @@ unsigned SCEVExpander::replaceCongruentI
                                                    IsomorphicInc->getType());
       if (OrigInc != IsomorphicInc && TruncExpr == SE.getSCEV(IsomorphicInc) &&
           SE.LI.replacementPreservesLCSSAForm(IsomorphicInc, OrigInc) &&
-          ((isa<PHINode>(OrigInc) && isa<PHINode>(IsomorphicInc)) ||
-           hoistIVInc(OrigInc, IsomorphicInc))) {
+          hoistIVInc(OrigInc, IsomorphicInc)) {
         DEBUG_WITH_TYPE(DebugType,
                         dbgs() << "INDVARS: Eliminated congruent iv.inc: "
                                << *IsomorphicInc << '\n');

Added: llvm/trunk/test/Analysis/ScalarEvolution/expander-replace-congruent-ivs.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/expander-replace-congruent-ivs.ll?rev=269212&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/expander-replace-congruent-ivs.ll (added)
+++ llvm/trunk/test/Analysis/ScalarEvolution/expander-replace-congruent-ivs.ll Wed May 11 12:41:34 2016
@@ -0,0 +1,41 @@
+; RUN: opt -S -indvars < %s | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.11.0"
+
+; SCEVExpander would try to RAUW %val_2 with %c.lcssa, breaking "def
+; dominates uses".
+
+define void @pr27232(i32 %val) {
+; CHECK-LABEL: @pr27232(
+entry:
+  br i1 undef, label %loop_0.cond, label %for.body.us
+
+for.body.us:
+  br label %loop_0.cond
+
+loop_0.cond:
+  %val_2 = phi i32 [ %val, %for.body.us ], [ undef, %entry ]
+  br i1 true, label %loop_0.ph, label %loop_1.ph
+
+loop_0.ph:
+  br label %loop_0
+
+loop_1.exit:
+  br label %loop_1.ph
+
+loop_1.ph:
+  %c.lcssa = phi i32 [ 0, %loop_0.cond ], [ %val_2, %loop_1.exit ]
+  br label %loop_1
+
+loop_0:
+  br i1 undef, label %loop_0, label %loop_1.exit
+
+loop_1:
+  %d.1 = phi i32 [ %c.lcssa, %loop_1 ], [ %val_2, %loop_1.ph ]
+  %t.1 = phi i32 [ %val_2, %loop_1 ], [ %c.lcssa, %loop_1.ph ]
+  br i1 undef, label %leave, label %loop_1
+
+leave:
+  ret void
+}