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llvm-project/llvm/test/Transforms/SimplifyCFG/switch_msan.ll

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[SimplifyCFG] Don't SimplifyBranchOnICmpChain with ExtraCase Summary: Here we try to avoid issues with "explicit branch" with SimplifyBranchOnICmpChain which can check on undef. Msan by design reports branches on uninitialized memory and undefs, so we have false report here. In general msan does not like when we convert ``` // If at least one of them is true we can MSAN is ok if another is undefs if (a || b) return; ``` into ``` // If 'a' is undef MSAN will complain even if 'b' is true if (a) return; if (b) return; ``` Example Before optimization we had something like this: ``` while (true) { bool maybe_undef = doStuff(); while (true) { char c = getChar(); if (c != 10 && c != 13) continue break; } // we know that c == 10 || c == 13 if we get here, // so msan know that branch is not affected by maybe_undef if (maybe_undef || c == 10 || c == 13) continue; return; } ``` SimplifyBranchOnICmpChain will convert that into ``` while (true) { bool maybe_undef = doStuff(); while (true) { char c = getChar(); if (c != 10 && c != 13) continue; break; } // however msan will complain here: if (maybe_undef) continue; // we know that c == 10 || c == 13, so either way we will get continue switch(c) { case 10: continue; case 13: continue; } return; } ``` Reviewers: eugenis, efriedma Reviewed By: eugenis, efriedma Subscribers: hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D67205 llvm-svn: 371138
2019-09-06 06:49:34 +08:00
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S -simplifycfg < %s | FileCheck %s
declare i8 @next_char();
define void @test_no_msan() {
; CHECK-LABEL: @test_no_msan(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[WHILE_BODY:%.*]]
; CHECK: while.body:
; CHECK-NEXT: br label [[WHILE_BODY_I:%.*]]
; CHECK: while.body.i:
; CHECK-NEXT: [[MAYBE_UNDEF:%.*]] = phi i1 [ undef, [[WHILE_BODY]] ], [ [[NEXT_MAYBE_UNDEF:%.*]], [[WHILE_BODY_I]] ]
; CHECK-NEXT: [[C:%.*]] = call fastcc signext i8 @next_char()
; CHECK-NEXT: [[C_10:%.*]] = icmp eq i8 [[C]], 10
; CHECK-NEXT: [[C_13:%.*]] = icmp eq i8 [[C]], 13
; CHECK-NEXT: [[C_10_OR_13:%.*]] = or i1 [[C_10]], [[C_13]]
; CHECK-NEXT: [[NEXT_MAYBE_UNDEF]] = or i1 [[MAYBE_UNDEF]], [[C_10_OR_13]]
; CHECK-NEXT: [[C_NOT_10_OR_13:%.*]] = xor i1 [[C_10_OR_13]], true
; CHECK-NEXT: br i1 [[C_NOT_10_OR_13]], label [[WHILE_BODY_I]], label [[WHILE_BODY_I_BREAK:%.*]]
; CHECK: while.body.i.break:
; CHECK-NEXT: br i1 [[MAYBE_UNDEF]], label [[WHILE_BODY]], label [[SWITCH_EARLY_TEST:%.*]]
; CHECK: switch.early.test:
; CHECK-NEXT: switch i8 [[C]], label [[RETURN:%.*]] [
; CHECK-NEXT: i8 13, label [[WHILE_BODY]]
; CHECK-NEXT: i8 10, label [[WHILE_BODY]]
; CHECK-NEXT: ]
; CHECK: return:
; CHECK-NEXT: ret void
;
entry:
br label %while.body
while.body:
br label %while.body.i
while.body.i:
%maybe_undef = phi i1 [ undef, %while.body ], [ %next_maybe_undef, %while.body.i ]
%c = call fastcc signext i8 @next_char()
%c_10 = icmp eq i8 %c, 10
%c_13 = icmp eq i8 %c, 13
%c_10_or_13 = or i1 %c_10, %c_13
%next_maybe_undef = or i1 %maybe_undef, %c_10_or_13
%c_not_10_or_13 = xor i1 %c_10_or_13, true
br i1 %c_not_10_or_13, label %while.body.i, label %while.body.i.break
while.body.i.break:
; NEXT_MAYBE_UNDEF is never undef if here
br i1 %next_maybe_undef, label %while.body, label %return
return:
ret void
}
define void @test_msan() sanitize_memory {
; CHECK-LABEL: @test_msan(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[WHILE_BODY:%.*]]
; CHECK: while.body:
; CHECK-NEXT: br label [[WHILE_BODY_I:%.*]]
; CHECK: while.body.i:
; CHECK-NEXT: [[MAYBE_UNDEF:%.*]] = phi i1 [ undef, [[WHILE_BODY]] ], [ [[NEXT_MAYBE_UNDEF:%.*]], [[WHILE_BODY_I]] ]
; CHECK-NEXT: [[C:%.*]] = call fastcc signext i8 @next_char()
; CHECK-NEXT: [[C_10:%.*]] = icmp eq i8 [[C]], 10
; CHECK-NEXT: [[C_13:%.*]] = icmp eq i8 [[C]], 13
; CHECK-NEXT: [[C_10_OR_13:%.*]] = or i1 [[C_10]], [[C_13]]
; CHECK-NEXT: [[NEXT_MAYBE_UNDEF]] = or i1 [[MAYBE_UNDEF]], [[C_10_OR_13]]
; CHECK-NEXT: [[C_NOT_10_OR_13:%.*]] = xor i1 [[C_10_OR_13]], true
; CHECK-NEXT: br i1 [[C_NOT_10_OR_13]], label [[WHILE_BODY_I]], label [[WHILE_BODY_I_BREAK:%.*]]
; CHECK: while.body.i.break:
; CHECK-NEXT: br i1 [[NEXT_MAYBE_UNDEF]], label [[WHILE_BODY]], label [[RETURN:%.*]]
; CHECK: return:
; CHECK-NEXT: ret void
;
entry:
br label %while.body
while.body:
br label %while.body.i
while.body.i:
%maybe_undef = phi i1 [ undef, %while.body ], [ %next_maybe_undef, %while.body.i ]
%c = call fastcc signext i8 @next_char()
%c_10 = icmp eq i8 %c, 10
%c_13 = icmp eq i8 %c, 13
%c_10_or_13 = or i1 %c_10, %c_13
%next_maybe_undef = or i1 %maybe_undef, %c_10_or_13
%c_not_10_or_13 = xor i1 %c_10_or_13, true
br i1 %c_not_10_or_13, label %while.body.i, label %while.body.i.break
while.body.i.break:
; NEXT_MAYBE_UNDEF is never undef if here
br i1 %next_maybe_undef, label %while.body, label %return
return:
ret void
}