[llvm] 3a39bb9 - [SelectionDAG] Use correct boolean representation in FoldConstantArithmetic
Bjorn Pettersson via llvm-commits
llvm-commits at lists.llvm.org
Thu Apr 28 09:42:27 PDT 2022
Author: Bjorn Pettersson
Date: 2022-04-28T18:42:16+02:00
New Revision: 3a39bb96ca812d1cbd027803112e94f701ad8687
URL: https://github.com/llvm/llvm-project/commit/3a39bb96ca812d1cbd027803112e94f701ad8687
DIFF: https://github.com/llvm/llvm-project/commit/3a39bb96ca812d1cbd027803112e94f701ad8687.diff
LOG: [SelectionDAG] Use correct boolean representation in FoldConstantArithmetic
The description of SETCC says
/// SetCC operator - This evaluates to a true value iff the condition is
/// true. If the result value type is not i1 then the high bits conform
/// to getBooleanContents.
Without this patch, we sign extended the i1 to the used larger type
regardless of getBooleanContents. This resulted in miscompiles, as
shown in the attached testcase that ended up returning -1 instead of
1 when using -mattr=+v.
Fixes https://github.com/llvm/llvm-project/issues/55168
Reviewed By: craig.topper
Differential Revision: https://reviews.llvm.org/D124618
Added:
llvm/test/CodeGen/RISCV/fold-vector-cmp.ll
Modified:
llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
Removed:
################################################################################
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 69e100c2366a6..d66798818706f 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -5580,9 +5580,14 @@ SDValue SelectionDAG::FoldConstantArithmetic(unsigned Opcode, const SDLoc &DL,
!llvm::all_of(Ops, IsScalarOrSameVectorSize))
return SDValue();
- // If we are comparing vectors, then the result needs to be a i1 boolean
- // that is then sign-extended back to the legal result type.
+ // If we are comparing vectors, then the result needs to be a i1 boolean that
+ // is then extended back to the legal result type depending on how booleans
+ // are represented.
EVT SVT = (Opcode == ISD::SETCC ? MVT::i1 : VT.getScalarType());
+ ISD::NodeType ExtendCode =
+ (Opcode == ISD::SETCC && SVT != VT.getScalarType())
+ ? TargetLowering::getExtendForContent(TLI->getBooleanContents(VT))
+ : ISD::SIGN_EXTEND;
// Find legal integer scalar type for constant promotion and
// ensure that its scalar size is at least as large as source.
@@ -5640,7 +5645,7 @@ SDValue SelectionDAG::FoldConstantArithmetic(unsigned Opcode, const SDLoc &DL,
// Legalize the (integer) scalar constant if necessary.
if (LegalSVT != SVT)
- ScalarResult = getNode(ISD::SIGN_EXTEND, DL, LegalSVT, ScalarResult);
+ ScalarResult = getNode(ExtendCode, DL, LegalSVT, ScalarResult);
// Scalar folding only succeeded if the result is a constant or UNDEF.
if (!ScalarResult.isUndef() && ScalarResult.getOpcode() != ISD::Constant &&
diff --git a/llvm/test/CodeGen/RISCV/fold-vector-cmp.ll b/llvm/test/CodeGen/RISCV/fold-vector-cmp.ll
new file mode 100644
index 0000000000000..cfe64ce48de12
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/fold-vector-cmp.ll
@@ -0,0 +1,17 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -start-after codegenprepare -mtriple=riscv64 -mattr=-v -o - %s | FileCheck %s
+; RUN: llc -start-after codegenprepare -mtriple=riscv64 -mattr=+v -o - %s | FileCheck %s
+
+; Reproducer for https://github.com/llvm/llvm-project/issues/55168.
+; We should always return 1 (and not -1).
+define i32 @test(i32 %call.i) {
+; CHECK-LABEL: test:
+; CHECK: # %bb.0:
+; CHECK-NEXT: li a0, 1
+; CHECK-NEXT: ret
+ %t2 = insertelement <2 x i32> <i32 poison, i32 -2147483648>, i32 %call.i, i64 0
+ %t3 = icmp slt <2 x i32> %t2, <i32 -2147483646, i32 -2147483646>
+ %t4 = zext <2 x i1> %t3 to <2 x i32>
+ %t6 = extractelement <2 x i32> %t4, i64 1
+ ret i32 %t6
+}
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