[llvm] r371111 - [IfConversion] Fix diamond conversion with unanalyzable branches.

[Hans Wennborg via llvm-commits]

Merged to release_90 in r371377.

On Thu, Sep 5, 2019 at 10:01 PM Eli Friedman via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
>
> Author: efriedma
> Date: Thu Sep  5 13:02:38 2019
> New Revision: 371111
>
> URL: http://llvm.org/viewvc/llvm-project?rev=371111&view=rev
> Log:
> [IfConversion] Fix diamond conversion with unanalyzable branches.
>
> The code was incorrectly counting the number of identical instructions,
> and therefore tried to predicate an instruction which should not have
> been predicated.  This could have various effects: a compiler crash,
> an assembler failure, a miscompile, or just generating an extra,
> unnecessary instruction.
>
> Instead of depending on TargetInstrInfo::removeBranch, which only
> works on analyzable branches, just remove all branch instructions.
>
> Fixes https://bugs.llvm.org/show_bug.cgi?id=43121 and
> https://bugs.llvm.org/show_bug.cgi?id=41121 .
>
> Differential Revision: https://reviews.llvm.org/D67203
>
>
> Added:
>     llvm/trunk/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir
> Modified:
>     llvm/trunk/lib/CodeGen/IfConversion.cpp
>
> Modified: llvm/trunk/lib/CodeGen/IfConversion.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/IfConversion.cpp?rev=371111&r1=371110&r2=371111&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/IfConversion.cpp (original)
> +++ llvm/trunk/lib/CodeGen/IfConversion.cpp Thu Sep  5 13:02:38 2019
> @@ -1758,9 +1758,15 @@ bool IfConverter::IfConvertDiamondCommon
>    if (!BBI1->IsBrAnalyzable)
>      verifySameBranchInstructions(&MBB1, &MBB2);
>  #endif
> -  BBI1->NonPredSize -= TII->removeBranch(*BBI1->BB);
> -  // Remove duplicated instructions.
> +  // Remove duplicated instructions from the tail of MBB1: any branch
> +  // instructions, and the common instructions counted by NumDups2.
>    DI1 = MBB1.end();
> +  while (DI1 != MBB1.begin()) {
> +    MachineBasicBlock::iterator Prev = std::prev(DI1);
> +    if (!Prev->isBranch() && !Prev->isDebugInstr())
> +      break;
> +    DI1 = Prev;
> +  }
>    for (unsigned i = 0; i != NumDups2; ) {
>      // NumDups2 only counted non-dbg_value instructions, so this won't
>      // run off the head of the list.
>
> Added: llvm/trunk/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir?rev=371111&view=auto
> ==============================================================================
> --- llvm/trunk/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir (added)
> +++ llvm/trunk/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir Thu Sep  5 13:02:38 2019
> @@ -0,0 +1,58 @@
> +# RUN: llc %s -o - -run-pass=if-converter | FileCheck %s
> +# Make sure we correctly if-convert blocks containing an INLINEASM_BR.
> +# CHECK: t2CMPri killed renamable $r2, 34
> +# CHECK-NEXT: $r0 = t2MOVi 2, 1, $cpsr, $noreg
> +# CHECK-NEXT: $r0 = t2MOVi 3, 0, killed $cpsr, $noreg, implicit killed $r0
> +# CHECK-NEXT: tBL 14, $noreg, @fn2
> +# CHECK-NEXT: INLINEASM_BR &"", 9, 13, 0, 13, blockaddress(@fn1, %ir-block.l_yes)
> +# CHECK-NEXT: t2B %bb.1, 14, $noreg
> +--- |
> +  target triple = "thumbv7-unknown-linux-gnueabi"
> +
> +  define dso_local void @fn1() {
> +  l_yes:
> +    ret void
> +  }
> +
> +  declare dso_local i32 @fn2(...)
> +...
> +---
> +name:            fn1
> +alignment:       1
> +tracksRegLiveness: true
> +body:             |
> +  bb.0:
> +    successors: %bb.1(0x40000000), %bb.2(0x40000000)
> +    liveins: $r0, $r1, $r2, $r4, $lr
> +
> +    $sp = frame-setup t2STMDB_UPD $sp, 14, $noreg, killed $r4, killed $lr
> +    t2CMPri killed renamable $r2, 34, 14, $noreg, implicit-def $cpsr
> +    t2Bcc %bb.2, 1, killed $cpsr
> +
> +  bb.1:
> +    successors: %bb.3(0x40000000), %bb.4(0x40000000)
> +    liveins: $r1
> +
> +    $r0 = t2MOVi 3, 14, $noreg, $noreg
> +    tBL 14, $noreg, @fn2, csr_aapcs, implicit-def dead $lr, implicit $sp, implicit $r0, implicit $r1, implicit-def $sp, implicit-def dead $r0
> +    INLINEASM_BR &"", 9, 13, 0, 13, blockaddress(@fn1, %ir-block.l_yes)
> +    t2B %bb.3, 14, $noreg
> +
> +  bb.2:
> +    successors: %bb.3(0x40000000), %bb.4(0x40000000)
> +    liveins: $r1
> +
> +    $r0 = t2MOVi 2, 14, $noreg, $noreg
> +    tBL 14, $noreg, @fn2, csr_aapcs, implicit-def dead $lr, implicit $sp, implicit $r0, implicit $r1, implicit-def $sp, implicit-def dead $r0
> +    INLINEASM_BR &"", 9, 13, 0, 13, blockaddress(@fn1, %ir-block.l_yes)
> +    t2B %bb.3, 14, $noreg
> +
> +  bb.3:
> +    successors: %bb.4(0x80000000)
> +
> +    INLINEASM &"", 1
> +
> +  bb.4.l_yes (address-taken):
> +    $sp = t2LDMIA_RET $sp, 14, $noreg, def $r4, def $pc
> +
> +...
>
>
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