[llvm] r308503 - [X86] Don't try to scale down if that exceeds the bitwidth.

[Hans Wennborg via llvm-commits]

On Wed, Jul 19, 2017 at 8:15 PM, Davide Italiano <davide at freebsd.org> wrote:
> On Wed, Jul 19, 2017 at 11:09 AM, Davide Italiano via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>> Author: davide
>> Date: Wed Jul 19 11:09:46 2017
>> New Revision: 308503
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=308503&view=rev
>> Log:
>> [X86] Don't try to scale down if that exceeds the bitwidth.
>>
>> Fixes the crash reported in PR33844.
>>
>> Added:
>>     llvm/trunk/test/CodeGen/X86/pr33844.ll
>> Modified:
>>     llvm/trunk/lib/Target/X86/X86ISelDAGToDAG.cpp
>>
>> Modified: llvm/trunk/lib/Target/X86/X86ISelDAGToDAG.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelDAGToDAG.cpp?rev=308503&r1=308502&r2=308503&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Target/X86/X86ISelDAGToDAG.cpp (original)
>> +++ llvm/trunk/lib/Target/X86/X86ISelDAGToDAG.cpp Wed Jul 19 11:09:46 2017
>> @@ -1055,7 +1055,10 @@ static bool foldMaskAndShiftToScale(Sele
>>
>>    // Scale the leading zero count down based on the actual size of the value.
>>    // Also scale it down based on the size of the shift.
>> -  MaskLZ -= (64 - X.getSimpleValueType().getSizeInBits()) + ShiftAmt;
>> +  unsigned ScaleDown = (64 - X.getSimpleValueType().getSizeInBits()) + ShiftAmt;
>> +  if (MaskLZ < ScaleDown)
>> +    return true;
>> +  MaskLZ -= ScaleDown;
>>
>>    // The final check is to ensure that any masked out high bits of X are
>>    // already known to be zero. Otherwise, the mask has a semantic impact
>>
>> Added: llvm/trunk/test/CodeGen/X86/pr33844.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/pr33844.ll?rev=308503&view=auto
>> ==============================================================================
>> --- llvm/trunk/test/CodeGen/X86/pr33844.ll (added)
>> +++ llvm/trunk/test/CodeGen/X86/pr33844.ll Wed Jul 19 11:09:46 2017
>> @@ -0,0 +1,38 @@
>> +; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
>> +; RUN: llc -o - %s | FileCheck %s
>> +
>> +target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
>> +target triple = "x86_64-unknown-linux-gnu"
>> +
>> + at global = external global i32
>> + at global.1 = external global i64
>> +
>> +define void @patatino() {
>> +; CHECK-LABEL: patatino:
>> +; CHECK:       # BB#0: # %bb
>> +; CHECK-NEXT:    movl {{.*}}(%rip), %eax
>> +; CHECK-NEXT:    movl %eax, %ecx
>> +; CHECK-NEXT:    shrl $31, %ecx
>> +; CHECK-NEXT:    addl $2147483647, %ecx # imm = 0x7FFFFFFF
>> +; CHECK-NEXT:    shrl $31, %ecx
>> +; CHECK-NEXT:    andl $62, %ecx
>> +; CHECK-NEXT:    andl $-536870912, %eax # imm = 0xE0000000
>> +; CHECK-NEXT:    orl %ecx, %eax
>> +; CHECK-NEXT:    movl %eax, {{.*}}(%rip)
>> +; CHECK-NEXT:    retq
>> +bb:
>> +  %tmp = load i32, i32* @global
>> +  %tmp1 = lshr i32 %tmp, 31
>> +  %tmp2 = add nuw nsw i32 %tmp1, 2147483647
>> +  %tmp3 = load i64, i64* @global.1
>> +  %tmp4 = shl i64 %tmp3, 23
>> +  %tmp5 = add nsw i64 %tmp4, 8388639
>> +  %tmp6 = trunc i64 %tmp5 to i32
>> +  %tmp7 = lshr i32 %tmp2, %tmp6
>> +  %tmp8 = load i32, i32* @global
>> +  %tmp9 = and i32 %tmp7, 62
>> +  %tmp10 = and i32 %tmp8, -536870912
>> +  %tmp11 = or i32 %tmp9, %tmp10
>> +  store i32 %tmp11, i32* @global
>> +  ret void
>> +}
>>
>>
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>
> Hans, we might consider backporting it to 5.0 once this has baked in
> the tree for a bit.
> I marked https://bugs.llvm.org/show_bug.cgi?id=33844 as "blocker" just
> to make sure it's in your radar.

Noted, thanks.