https://bugs.llvm.org/show_bug.cgi?id=49640
Bug ID: 49640
Summary: PowerPC: Invalid merging of immediates for D-Form
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: PowerPC
Assignee: unassignedb...@nondot.org
Reporter: nemanja.i....@gmail.com
CC: llvm-bugs@lists.llvm.org, nemanja.i....@gmail.com
Created attachment 24661
--> https://bugs.llvm.org/attachment.cgi?id=24661&action=edit
Eigen test reduced by creduce
When a D-Form instruction is fed by an add-immediate, we attempt to merge the
two immediates to form a single displacement so we can remove the
add-immediate.
However, we don't check whether the new displacement fits into a 16-bit signed
immediate field early enough. Namely, we do a sign-extend from 16 bits first
which will discard high bits and then we check whether the result is a 16-bit
signed immediate. It of course will always be.
The check needs to be moved prior to the sign-extend.
Reduced test case from Eigen attached.
To reproduce the problem:
clang -S -O3 -mcpu=pwr9 badDForm.cpp -o - 2>/dev/null | grep stfs
stfs 0, 25400(7)
stfs 0, 30480(7)
stfs 0, -29976(7)
stfs 0, -24896(7)
stfs 0, -19816(7)
The correct values (with the peephole turned off):
clang -S -O3 -mcpu=pwr9 badDForm.cpp -o - -mllvm --disable-ppc-peephole
2>/dev/null | grep stfs
stfs 0, 0(7)
stfs 0, 5080(7)
stfs 0, 10160(7)
stfs 0, 15240(7)
stfs 0, 20320(7)
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