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Support lowering of empty aggregates.
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This crash was pretty common while compiling Rust for iOS (armv7). Reason -
SjLj preparation step was lowering aggregate arguments as ExtractValue +
InsertValue. ExtractValue has assertion which checks that there is some data in
value, which is not true in case of empty (no fields) structures. Rust uses
them quite extensively so this patch uses a 'select true, %val, undef'
instruction to lower the argument.

Patch by Valerii Hiora.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212922 91177308-0d34-0410-b5e6-96231b3b80d8
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isanbard committed Jul 14, 2014
1 parent 13764f7 commit 5388e6f
Showing 2 changed files with 42 additions and 11 deletions.
22 changes: 11 additions & 11 deletions lib/CodeGen/SjLjEHPrepare.cpp
Original file line number Diff line number Diff line change
@@ -249,18 +249,18 @@ void SjLjEHPrepare::lowerIncomingArguments(Function &F) {
++AI) {
Type *Ty = AI->getType();

// Aggregate types can't be cast, but are legal argument types, so we have
// to handle them differently. We use an extract/insert pair as a
// lightweight method to achieve the same goal.
if (isa<StructType>(Ty) || isa<ArrayType>(Ty)) {
Instruction *EI = ExtractValueInst::Create(AI, 0, "", AfterAllocaInsPt);
Instruction *NI = InsertValueInst::Create(AI, EI, 0);
NI->insertAfter(EI);
AI->replaceAllUsesWith(NI);

// Set the operand of the instructions back to the AllocaInst.
EI->setOperand(0, AI);
NI->setOperand(0, AI);
// Aggregate types can't be cast, but are legal argument types,
// so we have to handle them differently. We use
// select i8 true, %arg, undef to achieve the same goal
Value *TrueValue = ConstantInt::getTrue(F.getContext());
Value *UndefValue = UndefValue::get(Ty);
Instruction *SI = SelectInst::Create(TrueValue, AI, UndefValue,
AI->getName() + ".tmp",
AfterAllocaInsPt);
AI->replaceAllUsesWith(SI);

SI->setOperand(1, AI);
} else {
// This is always a no-op cast because we're casting AI to AI->getType()
// so src and destination types are identical. BitCast is the only
31 changes: 31 additions & 0 deletions test/CodeGen/ARM/sjljehprepare-lower-empty-struct.ll
Original file line number Diff line number Diff line change
@@ -0,0 +1,31 @@
; RUN: llc -mtriple=armv7-apple-ios -O0 < %s | FileCheck %s
; RUN: llc -mtriple=armv7-apple-ios -O1 < %s | FileCheck %s
; RUN: llc -mtriple=armv7-apple-ios -O2 < %s | FileCheck %s
; RUN: llc -mtriple=armv7-apple-ios -O3 < %s | FileCheck %s

; SjLjEHPrepare shouldn't crash when lowering empty structs.
;
; Checks that between in case of empty structs used as arguments
; nothing happens, i.e. there are no instructions between
; __Unwind_SjLj_Register and actual @bar invocation


define i8* @foo({} %c) {
entry:
; CHECK: bl __Unwind_SjLj_Register
; CHECK-NEXT: {{[A-Z][a-zA-Z0-9]*}}:
; CHECK-NEXT: bl _bar
invoke void @bar ()
to label %unreachable unwind label %handler

unreachable:
unreachable

handler:
%tmp = landingpad { i8*, i32 } personality i8* bitcast (i32 (...)* @baz to i8*)
cleanup
resume { i8*, i32 } undef
}

declare void @bar()
declare i32 @baz(...)

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