[PATCH] D122053: [SelectionDAG][RISCV] Make RegsForValue::getCopyToRegs explicitly zero_extend constants.
Craig Topper via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Fri Mar 18 18:39:41 PDT 2022
craig.topper created this revision.
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ComputePHILiveOutRegInfo assumes that constant incoming values to
Phis will be zero extended if they aren't a legal type. To guarantee
that we should zero_extend rather than any_extend constants.
This fixes a bug for RISCV where any_extend of constants can be
treated as a sign_extend.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D122053
Files:
llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
llvm/test/CodeGen/RISCV/aext-to-sext.ll
Index: llvm/test/CodeGen/RISCV/aext-to-sext.ll
===================================================================
--- llvm/test/CodeGen/RISCV/aext-to-sext.ll
+++ llvm/test/CodeGen/RISCV/aext-to-sext.ll
@@ -80,19 +80,25 @@
; constants are zero extended for phi incoming values so an AssertZExt is
; created in 'merge' allowing the zext to be removed.
; SelectionDAG::getNode treats any_extend of i32 constants as sext for RISCV.
-; The code that creates phi incoming values in the predecessors creates an
-; any_extend for the constants which then gets treated as a sext by getNode.
-; This means the zext was not safe to remove.
+; This code used to miscompile because the code that creates phi incoming values
+; in the predecessors created any_extend for the constants which then gets
+; treated as a sext by getNode. This made the removal of the zext incorrect.
+; SelectionDAGBuilder now creates a zero_extend instead of an any_extend to
+; match the assumption.
+; FIXME: RISCV would prefer constant inputs to phis to be sign extended.
define i64 @miscompile(i32 %c) {
; RV64I-LABEL: miscompile:
; RV64I: # %bb.0:
-; RV64I-NEXT: sext.w a1, a0
+; RV64I-NEXT: sext.w a0, a0
+; RV64I-NEXT: beqz a0, .LBB2_2
+; RV64I-NEXT: # %bb.1:
; RV64I-NEXT: li a0, -1
-; RV64I-NEXT: beqz a1, .LBB2_2
-; RV64I-NEXT: # %bb.1: # %merge
+; RV64I-NEXT: srli a0, a0, 32
; RV64I-NEXT: ret
; RV64I-NEXT: .LBB2_2: # %iffalse
-; RV64I-NEXT: li a0, -2
+; RV64I-NEXT: li a0, 1
+; RV64I-NEXT: slli a0, a0, 32
+; RV64I-NEXT: addi a0, a0, -2
; RV64I-NEXT: ret
%a = icmp ne i32 %c, 0
br i1 %a, label %iftrue, label %iffalse
Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -918,7 +918,10 @@
CallConv.getValue(), RegVTs[Value])
: RegVTs[Value];
- if (ExtendKind == ISD::ANY_EXTEND && TLI.isZExtFree(Val, RegisterVT))
+ // We need to zero extend constants that are liveout to match assumptions
+ // in FunctionLoweringInfo::ComputePHILiveOutRegInfo.
+ if (ExtendKind == ISD::ANY_EXTEND &&
+ (TLI.isZExtFree(Val, RegisterVT) || isa<ConstantSDNode>(Val)))
ExtendKind = ISD::ZERO_EXTEND;
getCopyToParts(DAG, dl, Val.getValue(Val.getResNo() + Value), &Parts[Part],
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