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[SystemZ] Fix wrong-code generation for certain always-false conditions 

We've found another bug in the code generation logic conditions for a
certain class of always-false conditions, those of the form
   if ((a & 1) < 0)

These only reach the back end when compiling without optimization.

The bug was introduced by the choice of using TEST UNDER MASK
to implement a check for
   if ((a & MASK) < VAL)
as
   if ((a & MASK) == 0)

where VAL is less than the the lowest bit of MASK.  This is correct
in all cases except for VAL == 0, in which case the original
condition is always false, but the replacement isn't.

Fixed by excluding that particular case.

llvm-svn: 259381
This commit is contained in:
Ulrich Weigand 2016-02-01 18:31:19 +00:00
parent 6fdfa3dc32
commit 4a4d4ab7a4
2 changed files with 27 additions and 1 deletions
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2
llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
View File

@ -1849,7 +1849,7 @@ static unsigned getTestUnderMaskCond(unsigned BitSize, unsigned CCMask,
if (CCMask == SystemZ::CCMASK_CMP_NE)
return SystemZ::CCMASK_TM_SOME_1;
}
if (EffectivelyUnsigned && CmpVal <= Low) {
if (EffectivelyUnsigned && CmpVal > 0 && CmpVal <= Low) {
if (CCMask == SystemZ::CCMASK_CMP_LT)
return SystemZ::CCMASK_TM_ALL_0;
if (CCMask == SystemZ::CCMASK_CMP_GE)

26
llvm/test/CodeGen/SystemZ/int-cmp-53.ll Normal file
View File

@ -0,0 +1,26 @@
; This used to incorrectly use a TMLL for an always-false test at -O0.
;
; RUN: llc -O0 < %s -mtriple=s390x-linux-gnu | FileCheck %s
define void @test(i8 *%input, i32 *%result) {
entry:
; CHECK-NOT: tmll
%0 = load i8, i8* %input, align 1
%1 = trunc i8 %0 to i1
%2 = zext i1 %1 to i32
%3 = icmp sge i32 %2, 0
br i1 %3, label %if.then, label %if.else
if.then:
store i32 1, i32* %result, align 4
br label %return
if.else:
store i32 0, i32* %result, align 4
br label %return
return:
ret void
}