[DependenceAnalysis] collectUpperBound triggers asserts

[llvmbot]

Bugzilla Link	21585
Resolution	FIXED
Resolved on	May 20, 2015 13:20
Version	trunk
OS	All
Attachments	the test that triggers assertion failures
Reporter	LLVM Bugzilla Contributor
CC	@hfinkel,@sebpop

Extended Description

collectUpperBound assumes the type of the back edge count is no wider than the desired type (T). However, this assumption does not hold at least in strongSIVTest where the type of Delta may be narrower.

In the attached test case, the back edge count is i64 100, but the Delta (derived from i32 %i and i32 5) is of i32.

define void @​i32_subscript(i32* %a) {
entry:
br label %for.body

for.body:
%i = phi i32 [ 0, %entry ], [ %i.inc, %for.body ]
%a.addr = getelementptr i32* %a, i32 %i
%a.addr.2 = getelementptr i32* %a, i32 5
%0 = load i32* %a.addr, align 4
%1 = add i32 %0, 1
store i32 %1, i32* %a.addr.2, align 4
%i.inc = add nsw i32 %i, 1
%i.inc.ext = sext i32 %i to i64
%exitcond = icmp ne i64 %i.inc.ext, 100
br i1 %exitcond, label %for.body, label %for.end

for.end:
ret void
}

Note: this issue is similar to #18456 in that both are caused by sort of type mismatching. However, the type mismatch in #18456 is caused by removeMatchingExtensions, and this bug is not.

Jingyue

[llvmbot]

collectUpperBounds is used to match the type of the back edge count toward the type of the subscripts.

In the case that the back edge count is wider than T, truncate it.

I created a patch: http://reviews.llvm.org/D9455

[llvmbot]

Fixed in r237439.