4331f19d8b
Otherwise we end up with an extra conditional jump, following by an
unconditional jump off the end of a function. ie.
bb.0:
BT32rr ..
JCC_1 %bb.4 ...
bb.1:
BT32rr ..
JCC_1 %bb.2 ...
JMP_1 %bb.3
bb.2:
...
bb.3.unreachable:
bb.4:
...
Should be equivalent to:
bb.0:
BT32rr ..
JCC_1 %bb.4 ...
JMP_1 %bb.2
bb.1:
bb.2:
...
bb.3.unreachable:
bb.4:
...
This can occur since at the higher level IR (Instruction) SwitchInsts
are required to have BBs for default destinations, even when it can be
deduced that such BBs are unreachable.
For most programs, this isn't an issue, just wasted instructions since the
unreachable has been statically proven.
The x86_64 Linux kernel when built with CONFIG_LTO_CLANG_THIN=y fails to
boot though once D106056 is re-applied. D106056 makes it more likely
that correlation-propagation (CVP) can deduce that the default case of
SwitchInsts are unreachable. The x86_64 kernel uses a binary post
processor called objtool, which emits this warning:
vmlinux.o: warning: objtool: cfg80211_edmg_chandef_valid()+0x169: can't
find jump dest instruction at .text.cfg80211_edmg_chandef_valid+0x17b
I haven't debugged precisely why this causes a failure at boot time, but
fixing this very obvious jump off the end of the function fixes the
warning and boot problem.
Link: https://bugs.llvm.org/show_bug.cgi?id=50080
Fixes: https://github.com/ClangBuiltLinux/linux/issues/679
Fixes: https://github.com/ClangBuiltLinux/linux/issues/1440
Reviewed By: hans
Differential Revision: https://reviews.llvm.org/D109103
106 lines
3.3 KiB
LLVM
106 lines
3.3 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
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; RUN: llc < %s -mtriple=i686-- | FileCheck %s
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; PR964
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define i8* @FindChar(i8* %CurPtr) {
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; CHECK-LABEL: FindChar:
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; CHECK: # %bb.0: # %entry
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; CHECK-NEXT: pushl %edi
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; CHECK-NEXT: .cfi_def_cfa_offset 8
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; CHECK-NEXT: pushl %esi
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; CHECK-NEXT: .cfi_def_cfa_offset 12
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; CHECK-NEXT: .cfi_offset %esi, -12
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; CHECK-NEXT: .cfi_offset %edi, -8
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; CHECK-NEXT: xorl %edi, %edi
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; CHECK-NEXT: movl {{[0-9]+}}(%esp), %esi
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; CHECK-NEXT: .p2align 4, 0x90
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; CHECK-NEXT: .LBB0_1: # %bb
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; CHECK-NEXT: # =>This Inner Loop Header: Depth=1
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; CHECK-NEXT: movzbl (%esi,%edi), %eax
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; CHECK-NEXT: incl %edi
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; CHECK-NEXT: cmpb $120, %al
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; CHECK-NEXT: je .LBB0_3
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; CHECK-NEXT: # %bb.2: # %bb
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; CHECK-NEXT: # in Loop: Header=BB0_1 Depth=1
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; CHECK-NEXT: testb %al, %al
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; CHECK-NEXT: jne .LBB0_1
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; CHECK-NEXT: .LBB0_3: # %bb7
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; CHECK-NEXT: movzbl %al, %eax
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; CHECK-NEXT: pushl %eax
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; CHECK-NEXT: .cfi_adjust_cfa_offset 4
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; CHECK-NEXT: calll foo@PLT
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; CHECK-NEXT: addl $4, %esp
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; CHECK-NEXT: .cfi_adjust_cfa_offset -4
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; CHECK-NEXT: addl %edi, %esi
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; CHECK-NEXT: movl %esi, %eax
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; CHECK-NEXT: popl %esi
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; CHECK-NEXT: .cfi_def_cfa_offset 8
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; CHECK-NEXT: popl %edi
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; CHECK-NEXT: .cfi_def_cfa_offset 4
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; CHECK-NEXT: retl
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entry:
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br label %bb
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bb: ; preds = %bb, %entry
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%indvar = phi i32 [ 0, %entry ], [ %indvar.next, %bb ] ; <i32> [#uses=3]
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%CurPtr_addr.0.rec = bitcast i32 %indvar to i32 ; <i32> [#uses=1]
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%gep.upgrd.1 = zext i32 %indvar to i64 ; <i64> [#uses=1]
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%CurPtr_addr.0 = getelementptr i8, i8* %CurPtr, i64 %gep.upgrd.1 ; <i8*> [#uses=1]
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%tmp = load i8, i8* %CurPtr_addr.0 ; <i8> [#uses=3]
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%tmp2.rec = add i32 %CurPtr_addr.0.rec, 1 ; <i32> [#uses=1]
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%tmp2 = getelementptr i8, i8* %CurPtr, i32 %tmp2.rec ; <i8*> [#uses=1]
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%indvar.next = add i32 %indvar, 1 ; <i32> [#uses=1]
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switch i8 %tmp, label %bb [
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i8 0, label %bb7
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i8 120, label %bb7
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]
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bb7: ; preds = %bb, %bb
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tail call void @foo( i8 %tmp )
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ret i8* %tmp2
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}
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declare void @foo(i8)
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; PR50080
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; The important part of this test is that we emit only 1 bit test rather than
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; 2 since the default BB of the switch is unreachable.
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define i32 @baz(i32 %0) {
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; CHECK-LABEL: baz:
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; CHECK: # %bb.0:
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; CHECK-NEXT: xorl %eax, %eax
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; CHECK-NEXT: movl {{[0-9]+}}(%esp), %ecx
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; CHECK-NEXT: movl $13056, %edx # imm = 0x3300
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; CHECK-NEXT: btl %ecx, %edx
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; CHECK-NEXT: jae .LBB1_1
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; CHECK-NEXT: # %bb.2: # %return
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; CHECK-NEXT: retl
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; CHECK-NEXT: .LBB1_1: # %sw.epilog8
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; CHECK-NEXT: movl $1, %eax
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; CHECK-NEXT: retl
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switch i32 %0, label %if.then.unreachabledefault [
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i32 4, label %sw.epilog8
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i32 5, label %sw.epilog8
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i32 8, label %sw.bb2
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i32 9, label %sw.bb2
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i32 12, label %sw.bb4
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i32 13, label %sw.bb4
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]
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sw.bb2:
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br label %return
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sw.bb4:
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br label %return
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sw.epilog8:
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br label %return
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if.then.unreachabledefault:
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unreachable
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return:
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%retval.0 = phi i32 [ 1, %sw.epilog8 ], [ 0, %sw.bb2 ], [ 0, %sw.bb4 ]
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ret i32 %retval.0
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}
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