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Fix PR45371: SeparateConstOffsetFromGEP clean up bookkeeping

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find() was altering the UserChain, even in cases where it subsequently
discovered that the resulting constant was a 0. This confuses
rebuildWithoutConstOffset() when it attempts to walk the chain later, since it
is expected that the chain itself be a path down the use-def edges of an
expression.
This commit is contained in:
Jonathan Roelofs 2020-03-31 13:11:19 -06:00
parent 36f540bc9f
commit 763969726a
2 changed files with 37 additions and 1 deletions
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15
lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
View File

@ -522,7 +522,7 @@ bool ConstantOffsetExtractor::CanTraceInto(bool SignExtended,
// sext(a + b) = sext(a) + sext(b)
// even if the addition is not marked nsw.
//
// Leveraging this invarient, we can trace into an sext'ed inbound GEP
// Leveraging this invariant, we can trace into an sext'ed inbound GEP
// index if the constant offset is non-negative.
//
// Verified in @sext_add in split-gep.ll.
@ -552,6 +552,9 @@ bool ConstantOffsetExtractor::CanTraceInto(bool SignExtended,
APInt ConstantOffsetExtractor::findInEitherOperand(BinaryOperator *BO,
bool SignExtended,
bool ZeroExtended) {
// Save off the current height of the chain, in case we need to restore it.
size_t ChainLength = UserChain.size();
// BO being non-negative does not shed light on whether its operands are
// non-negative. Clear the NonNegative flag here.
APInt ConstantOffset = find(BO->getOperand(0), SignExtended, ZeroExtended,
@ -562,12 +565,22 @@ APInt ConstantOffsetExtractor::findInEitherOperand(BinaryOperator *BO,
// However, such cases are probably already handled by -instcombine,
// given this pass runs after the standard optimizations.
if (ConstantOffset != 0) return ConstantOffset;
// Reset the chain back to where it was when we started exploring this node,
// since visiting the LHS didn't pan out.
UserChain.resize(ChainLength);
ConstantOffset = find(BO->getOperand(1), SignExtended, ZeroExtended,
/* NonNegative */ false);
// If U is a sub operator, negate the constant offset found in the right
// operand.
if (BO->getOpcode() == Instruction::Sub)
ConstantOffset = -ConstantOffset;
// If RHS wasn't a suitable candidate either, reset the chain again.
if (ConstantOffset == 0)
UserChain.resize(ChainLength);
return ConstantOffset;
}

23
test/Transforms/SeparateConstOffsetFromGEP/pr45371-find-either-reset.ll Normal file
View File

@ -0,0 +1,23 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S -separate-const-offset-from-gep < %s | FileCheck %s
@e = external global [4000 x i8], align 1
define void @find_either_reset() {
; CHECK-LABEL: @find_either_reset(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SUB:%.*]] = sub nsw i32 65536, undef
; CHECK-NEXT: [[TMP0:%.*]] = trunc i32 [[SUB]] to i8
; CHECK-NEXT: [[TMP1:%.*]] = add i8 [[TMP0]], 96
; CHECK-NEXT: [[IDXPROM:%.*]] = sext i8 0 to i64
; CHECK-NEXT: [[IDXPROM1:%.*]] = sext i8 [[TMP1]] to i64
; CHECK-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds [4000 x i8], [4000 x i8]* @e, i64 [[IDXPROM]], i64 [[IDXPROM1]]
; CHECK-NEXT: ret void
;
entry:
%sub = sub nsw i32 65536, undef
%0 = trunc i32 %sub to i8
%1 = add i8 %0, -4000
%arrayidx = getelementptr inbounds [4000 x i8], [4000 x i8]* @e, i8 0, i8 %1
ret void
}