http://llvm.org/bugs/show_bug.cgi?id=4917
Summary: Optimize mul and unsigned compare to mul-with-overflow
Product: libraries
Version: trunk
Platform: PC
URL: http://codepad.org/qIPeNgVm
OS/Version: All
Status: NEW
Severity: normal
Priority: P2
Component: Scalar Optimizations
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
This is a forwarded complaint by "bearophile" on LLVM IRC, who unfortunately
never files bugs.
The URL contains an unreduced test case.
The following should be optimized to a mul-with-overflow:
%L_ext = zext i32 %L to i64
%R_ext = zext i32 %R to i64
%mul64 = mul i64 %L_ext, %R_ext # no uses except the following:
%overflow = icmp ugt i64 %mul64, (i64 0xffffffff)
br i1 %overflow, label %elsewhere, label %cont
...
%mul32 = mul i32 %L, %R
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