[llvm] 7ef6f01 - [SimplifyCFG] FoldTwoEntryPHINode(): bailout on inverted logical and/or (PR51149)

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2021-07-22T22:19:34+03:00
New Revision: 7ef6f019090f3979fa345105b9ac95ac589c6cf9

URL: https://github.com/llvm/llvm-project/commit/7ef6f019090f3979fa345105b9ac95ac589c6cf9
DIFF: https://github.com/llvm/llvm-project/commit/7ef6f019090f3979fa345105b9ac95ac589c6cf9.diff

LOG: [SimplifyCFG] FoldTwoEntryPHINode(): bailout on inverted logical and/or (PR51149)

The logical (select) form of and/or will now be a source of problems.
We don't really account for it's inverted form, yet it exists,
and presumably we should treat it just like non-inverted form:
https://alive2.llvm.org/ce/z/BU9AXk

https://bugs.llvm.org/show_bug.cgi?id=51149 reports a reportedly-serious
perf regression that will hopefully be mitigated by this.

Added: 
    

Modified: 
    llvm/lib/Transforms/Utils/SimplifyCFG.cpp
    llvm/test/Transforms/SimplifyCFG/two-entry-phi-node.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 04983ac39d05..399e37efe0ed 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2771,12 +2771,15 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
   };
 
   // Don't fold i1 branches on PHIs which contain binary operators or
-  // select form of or/ands, unless one of the incoming values is an 'not' and
-  // another one is freely invertible.
+  // (possibly inverted) select form of or/ands,  unless one of
+  // the incoming values is an 'not' and another one is freely invertible.
   // These can often be turned into switches and other things.
   auto IsBinOpOrAnd = [](Value *V) {
     return match(
-        V, m_CombineOr(m_BinOp(), m_CombineOr(m_LogicalAnd(), m_LogicalOr())));
+        V, m_CombineOr(
+               m_BinOp(),
+               m_CombineOr(m_Select(m_Value(), m_ImmConstant(), m_Value()),
+                           m_Select(m_Value(), m_Value(), m_ImmConstant()))));
   };
   if (PN->getType()->isIntegerTy(1) &&
       (IsBinOpOrAnd(PN->getIncomingValue(0)) ||

diff  --git a/llvm/test/Transforms/SimplifyCFG/two-entry-phi-node.ll b/llvm/test/Transforms/SimplifyCFG/two-entry-phi-node.ll
index bb5671bc1724..460b4aaba1a4 100644
--- a/llvm/test/Transforms/SimplifyCFG/two-entry-phi-node.ll
+++ b/llvm/test/Transforms/SimplifyCFG/two-entry-phi-node.ll
@@ -200,10 +200,14 @@ define i1 @t6_nor_logical2(i8 %v0, i8 %v1, i8 %v2, i1 %v3) {
 ; CHECK-LABEL: @t6_nor_logical2(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[C0:%.*]] = icmp eq i8 [[V0:%.*]], 0
+; CHECK-NEXT:    br i1 [[C0]], label [[PRED0:%.*]], label [[END:%.*]]
+; CHECK:       pred0:
 ; CHECK-NEXT:    [[C1:%.*]] = icmp eq i8 [[V1:%.*]], 0
 ; CHECK-NEXT:    [[C2:%.*]] = icmp ne i8 [[V2:%.*]], 0
 ; CHECK-NEXT:    [[COMPUTED:%.*]] = select i1 [[C1]], i1 false, i1 [[C2]]
-; CHECK-NEXT:    [[R:%.*]] = select i1 [[C0]], i1 [[COMPUTED]], i1 [[V3:%.*]]
+; CHECK-NEXT:    br label [[END]]
+; CHECK:       end:
+; CHECK-NEXT:    [[R:%.*]] = phi i1 [ [[COMPUTED]], [[PRED0]] ], [ [[V3:%.*]], [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    ret i1 [[R]]
 ;
 entry:
@@ -290,10 +294,14 @@ define i1 @t9_nand_logical2(i8 %v0, i8 %v1, i8 %v2, i1 %v3) {
 ; CHECK-LABEL: @t9_nand_logical2(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[C0:%.*]] = icmp eq i8 [[V0:%.*]], 0
+; CHECK-NEXT:    br i1 [[C0]], label [[PRED0:%.*]], label [[END:%.*]]
+; CHECK:       pred0:
 ; CHECK-NEXT:    [[C1:%.*]] = icmp eq i8 [[V1:%.*]], 0
 ; CHECK-NEXT:    [[C2:%.*]] = icmp ne i8 [[V2:%.*]], 0
 ; CHECK-NEXT:    [[COMPUTED:%.*]] = select i1 [[C1]], i1 [[C2]], i1 true
-; CHECK-NEXT:    [[R:%.*]] = select i1 [[C0]], i1 [[COMPUTED]], i1 [[V3:%.*]]
+; CHECK-NEXT:    br label [[END]]
+; CHECK:       end:
+; CHECK-NEXT:    [[R:%.*]] = phi i1 [ [[COMPUTED]], [[PRED0]] ], [ [[V3:%.*]], [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    ret i1 [[R]]
 ;
 entry: