[llvm] r319818 - [SystemZ] Validate shifted compare value in adjustForTestUnderMask

[Ulrich Weigand via llvm-commits]

Author: uweigand
Date: Tue Dec  5 11:42:07 2017
New Revision: 319818

URL: http://llvm.org/viewvc/llvm-project?rev=319818&view=rev
Log:
[SystemZ] Validate shifted compare value in adjustForTestUnderMask

When folding a shift into a test-under-mask comparison, make sure that
there is no loss of precision when creating the shifted comparison
value.  This usually never happens, except for certain always-true
comparisons in unoptimized code.

Fixes PR35529.


Modified:
    llvm/trunk/lib/Target/SystemZ/SystemZISelLowering.cpp
    llvm/trunk/test/CodeGen/SystemZ/int-cmp-47.ll

Modified: llvm/trunk/lib/Target/SystemZ/SystemZISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/SystemZ/SystemZISelLowering.cpp?rev=319818&r1=319817&r2=319818&view=diff
==============================================================================
--- llvm/trunk/lib/Target/SystemZ/SystemZISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/SystemZ/SystemZISelLowering.cpp Tue Dec  5 11:42:07 2017
@@ -2201,6 +2201,7 @@ static void adjustForTestUnderMask(Selec
       NewC.Op0.getOpcode() == ISD::SHL &&
       isSimpleShift(NewC.Op0, ShiftVal) &&
       (MaskVal >> ShiftVal != 0) &&
+      ((CmpVal >> ShiftVal) << ShiftVal) == CmpVal &&
       (NewCCMask = getTestUnderMaskCond(BitSize, NewC.CCMask,
                                         MaskVal >> ShiftVal,
                                         CmpVal >> ShiftVal,
@@ -2211,6 +2212,7 @@ static void adjustForTestUnderMask(Selec
              NewC.Op0.getOpcode() == ISD::SRL &&
              isSimpleShift(NewC.Op0, ShiftVal) &&
              (MaskVal << ShiftVal != 0) &&
+             ((CmpVal << ShiftVal) >> ShiftVal) == CmpVal &&
              (NewCCMask = getTestUnderMaskCond(BitSize, NewC.CCMask,
                                                MaskVal << ShiftVal,
                                                CmpVal << ShiftVal,

Modified: llvm/trunk/test/CodeGen/SystemZ/int-cmp-47.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/SystemZ/int-cmp-47.ll?rev=319818&r1=319817&r2=319818&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/SystemZ/int-cmp-47.ll (original)
+++ llvm/trunk/test/CodeGen/SystemZ/int-cmp-47.ll Tue Dec  5 11:42:07 2017
@@ -342,3 +342,25 @@ store:
 exit:
   ret void
 }
+
+; Check that we don't fold a shift if the comparison value
+; would need to be shifted out of range
+define void @f19(i64 %a) {
+; CHECK-LABEL: f19:
+; CHECK-NOT: tmhh
+; CHECK: srlg [[REG:%r[0-5]]], %r2, 63
+; CHECK: cgibl [[REG]], 3, 0(%r14)
+; CHECK: br %r14
+entry:
+  %shr = lshr i64 %a, 63
+  %cmp = icmp ult i64 %shr, 3
+  br i1 %cmp, label %exit, label %store
+
+store:
+  store i32 1, i32 *@g
+  br label %exit
+
+exit:
+  ret void
+}
+