http://llvm.org/bugs/show_bug.cgi?id=7416
Summary: scev miscomputes multi-backedge loop
Product: libraries
Version: trunk
Platform: PC
OS/Version: Linux
Status: NEW
Severity: normal
Priority: P
Component: Loop Optimizer
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Created an attachment (id=5056)
--> (http://llvm.org/bugs/attachment.cgi?id=5056)
hand-coded testcase
The attached program shows a loop from 0 to 100 in steppings of either 2 or 3
each iteration as controlled by an external function. SCEV claims that this has
a max backedge-taken count of 50 (perfect!) and that the exact backedge-taken
count is also 50. Oops!
$ opt -analyze -scalar-evolution loop.ll
Printing analysis 'Scalar Evolution Analysis' for function 'f':
Classifying expressions for: @f
%x = phi i32 [ 0, %entry ], [ %x.1, %bb1 ], [ %x.2, %bb2 ] ; <i32> [#uses=3]
--> %x Exits: 100
%z = call i1 @g() ; <i1> [#uses=1]
--> %z Exits: <<Unknown>>
%x.1 = add i32 %x, 2 ; <i32> [#uses=1]
--> (2 + %x) Exits: 102
%x.2 = add i32 %x, 3 ; <i32> [#uses=1]
--> (3 + %x) Exits: 103
Determining loop execution counts for: @f
Loop %loophead: backedge-taken count is 50
Loop %loophead: max backedge-taken count is 50
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