[llvm-bugs] [Bug 34042] New: [X86] Unnecessary sign extension in bextr second arg
via llvm-bugs
llvm-bugs at lists.llvm.org
Thu Aug 3 05:16:01 PDT 2017
https://bugs.llvm.org/show_bug.cgi?id=34042
Bug ID: 34042
Summary: [X86] Unnecessary sign extension in bextr second arg
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: unassignedbugs at nondot.org
Reporter: llvm-dev at redking.me.uk
CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
spatel+llvm at rotateright.com
#include <stdint.h>
uint64_t bextr64_demanded(uint64_t a, int32_t b)
{
return __builtin_ia32_bextr_u64(a, b);
}
define i64 @bextr64_demanded(i64, i32) {
%3 = sext i32 %1 to i64
%4 = tail call i64 @llvm.x86.bmi.bextr.64(i64 %0, i64 %3)
ret i64 %4
}
declare i64 @llvm.x86.bmi.bextr.64(i64, i64)
bextr64_demanded:
movslq %esi, %rax
bextrq %rax, %rdi, %rax
retq
As only the bottom 16 bits of the second argument is needed for BEXTR we are
performing an unnecessary sign extension.
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