[llvm] r298845 - [InstCombine] Avoid incorrect folding of select into phi nodes when incoming element is a vector type
Anna Thomas via llvm-commits
llvm-commits at lists.llvm.org
Mon Mar 27 06:52:51 PDT 2017
Author: annat
Date: Mon Mar 27 08:52:51 2017
New Revision: 298845
URL: http://llvm.org/viewvc/llvm-project?rev=298845&view=rev
Log:
[InstCombine] Avoid incorrect folding of select into phi nodes when incoming element is a vector type
Summary:
We are incorrectly folding selects into phi nodes when the incoming value of a phi
node is a constant vector. This optimization is done in `FoldOpIntoPhi` when the
select condition is a phi node with constant incoming values.
Without the fix, we are miscompiling (i.e. incorrectly folding the
select into the phi node) when the vector contains non-zero
elements.
This patch fixes the miscompile and we will correctly fold based on the
select vector operand (see added test cases).
Reviewers: majnemer, sanjoy, spatel
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D31189
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
llvm/trunk/test/Transforms/InstCombine/phi-select-constexpr.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp?rev=298845&r1=298844&r2=298845&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp Mon Mar 27 08:52:51 2017
@@ -908,7 +908,11 @@ Instruction *InstCombiner::FoldOpIntoPhi
// Beware of ConstantExpr: it may eventually evaluate to getNullValue,
// even if currently isNullValue gives false.
Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i));
- if (InC && !isa<ConstantExpr>(InC))
+ // For vector constants, we cannot use isNullValue to fold into
+ // FalseVInPred versus TrueVInPred. When we have individual nonzero
+ // elements in the vector, we will incorrectly fold InC to
+ // `TrueVInPred`.
+ if (InC && !isa<ConstantExpr>(InC) && !isa<VectorType>(InC->getType()))
InV = InC->isNullValue() ? FalseVInPred : TrueVInPred;
else
InV = Builder->CreateSelect(PN->getIncomingValue(i),
Modified: llvm/trunk/test/Transforms/InstCombine/phi-select-constexpr.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/phi-select-constexpr.ll?rev=298845&r1=298844&r2=298845&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/phi-select-constexpr.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/phi-select-constexpr.ll Mon Mar 27 08:52:51 2017
@@ -9,6 +9,7 @@ entry:
delay:
br label %final
+; CHECK-LABEL: @foo
; CHECK-LABEL: final:
; CHECK: phi i32 [ 1, %entry ], [ select (i1 icmp eq (i32* @A, i32* @B), i32 2, i32 1), %delay ]
final:
@@ -17,3 +18,40 @@ final:
ret i32 %value
}
+
+; test folding of select into phi for vectors.
+define <4 x i64> @vec1(i1 %which) {
+entry:
+ br i1 %which, label %final, label %delay
+
+delay:
+ br label %final
+
+final:
+; CHECK-LABEL: @vec1
+; CHECK-LABEL: final:
+; CHECK: %phinode = phi <4 x i64> [ zeroinitializer, %entry ], [ <i64 0, i64 0, i64 126, i64 127>, %delay ]
+; CHECK-NOT: select
+; CHECK: ret <4 x i64> %phinode
+ %phinode = phi <4 x i1> [ <i1 true, i1 true, i1 true, i1 true>, %entry ], [ <i1 true, i1 true, i1 false, i1 false>, %delay ]
+ %sel = select <4 x i1> %phinode, <4 x i64> zeroinitializer, <4 x i64> <i64 124, i64 125, i64 126, i64 127>
+ ret <4 x i64> %sel
+}
+
+define <4 x i64> @vec2(i1 %which) {
+entry:
+ br i1 %which, label %final, label %delay
+
+delay:
+ br label %final
+
+final:
+; CHECK-LABEL: @vec2
+; CHECK-LABEL: final:
+; CHECK: %phinode = phi <4 x i64> [ <i64 124, i64 125, i64 126, i64 127>, %entry ], [ <i64 0, i64 125, i64 0, i64 127>, %delay ]
+; CHECK-NOT: select
+; CHECK: ret <4 x i64> %phinode
+ %phinode = phi <4 x i1> [ <i1 false, i1 false, i1 false, i1 false>, %entry ], [ <i1 true, i1 false, i1 true, i1 false>, %delay ]
+ %sel = select <4 x i1> %phinode, <4 x i64> zeroinitializer, <4 x i64> <i64 124, i64 125, i64 126, i64 127>
+ ret <4 x i64> %sel
+}
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