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[ValueTracking] don't crash when assumptions conflict (PR36270)

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The last assume in the test says that %B12 is 0. 
The first assume says that %and1 is less than %B12. 
Therefore, %and1 is unsigned less than 0...does not compute.

That means this line:
Known.Zero.setHighBits(RHSKnown.countMinLeadingZeros() + 1);
...tries to set more bits than exist.

Differential Revision: https://reviews.llvm.org/D43052

llvm-svn: 324610
This commit is contained in:
Sanjay Patel 2018-02-08 14:52:40 +00:00
parent 2ee410c019
commit ca7a21e000
2 changed files with 29 additions and 0 deletions
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8
lib/Analysis/ValueTracking.cpp
View File

@ -816,6 +816,14 @@ static void computeKnownBitsFromAssume(const Value *V, KnownBits &Known,
KnownBits RHSKnown(BitWidth);
computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I));
// If the RHS is known zero, then this assumption must be wrong (nothing
// is unsigned less than zero). Signal a conflict and get out of here.
if (RHSKnown.isZero()) {
Known.Zero.setAllBits();
Known.One.setAllBits();
break;
}
// Whatever high bits in c are zero are known to be zero (if c is a power
// of 2, then one more).
if (isKnownToBeAPowerOfTwo(A, false, Depth + 1, Query(Q, I)))

21
test/Transforms/InstSimplify/assume.ll
View File

@ -5,6 +5,7 @@
; CHECK: remark: /tmp/s.c:1:13: Detected conflicting code assumptions.
; CHECK: remark: /tmp/s.c:4:10: Detected conflicting code assumptions.
; CHECK: remark: /tmp/s.c:5:50: Detected conflicting code assumptions.
define void @test1() {
; CHECK-LABEL: @test1(
@ -50,6 +51,24 @@ define i8 @conflicting_assumptions(i8 %x) !dbg !10 {
ret i8 %add
}
; Another case of conflicting assumptions. This would crash because we'd
; try to set more known bits than existed in the known bits struct.
define void @PR36270(i32 %b) !dbg !13 {
; CHECK-LABEL: @PR36270(
; CHECK-NEXT: tail call void @llvm.assume(i1 false)
; CHECK-NEXT: unreachable
;
%B7 = xor i32 -1, 2147483647
%and1 = and i32 %b, 3
%B12 = lshr i32 %B7, %and1, !dbg !14
%C1 = icmp ult i32 %and1, %B12
tail call void @llvm.assume(i1 %C1)
%cmp2 = icmp eq i32 0, %B12
tail call void @llvm.assume(i1 %cmp2)
unreachable
}
declare void @llvm.assume(i1) nounwind
!llvm.dbg.cu = !{!0}
@ -69,4 +88,6 @@ declare void @llvm.assume(i1) nounwind
!10 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 3, type: !8, isLocal: false, isDefinition: true, scopeLine: 3, isOptimized: true, unit: !0, variables: !2)
!11 = !DILocation(line: 4, column: 10, scope: !10)
!12 = !DILocation(line: 4, column: 3, scope: !10)
!13 = distinct !DISubprogram(name: "PR36270", scope: !1, file: !1, line: 3, type: !8, isLocal: false, isDefinition: true, scopeLine: 3, isOptimized: true, unit: !0, variables: !2)
!14 = !DILocation(line: 5, column: 50, scope: !13)