https://llvm.org/bugs/show_bug.cgi?id=29009
Bug ID: 29009
Summary: Redundent and instruction caused by switch condition
operand shrinking
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: w...@google.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Created attachment 16969
--> https://llvm.org/bugs/attachment.cgi?id=16969&action=edit
testcase 1.cc
For the testcase 1.cc attached.
~/workarea/llvm-r278451/dbuild/bin/clang -O2 -S 1.cc
Here is the code to generate the index to access jump table:
movl njob(%rip), %eax
callq _Z3goov
movl %eax, %edx
andb $7, %dl
movl %eax, %ecx
andl $7, %ecx // There is redundency to compute "and $7, ..."
twice.
cmpb $7, %dl
je .LBB0_3
# BB#2: # %while.cond
# in Loop: Header=BB0_1 Depth=1
jmpq *.LJTI0_0(,%rcx,8)
Better code is:
.LBB0_1: # =>This Inner Loop Header: Depth=1
movl njob(%rip), %eax
callq _Z3goov
movl %eax, %ecx
andl $7, %ecx
cmpl $6, %ecx
ja .LBB0_3
# BB#2: # in Loop: Header=BB0_1 Depth=1
jmpq *.LJTI0_0(,%rcx,8)
Looks like it is caused by r274233 which allows illegal type generated when
shrinking switch condition operand.
--
You are receiving this mail because:
You are on the CC list for the bug.
_______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
