https://bugs.llvm.org/show_bug.cgi?id=48734
Bug ID: 48734
Summary: [NPM] Slower arm_mult_q15 code from failing to
simplify min/max pattern
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Interprocedural Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
This code does a saturating multiply of 16bit fixed point values.
https://godbolt.org/z/9Eo1rz
It is roughly ~55% slower under the new pass manager (larger with q7 data
types). It appears that the code pattern under the old pass manager contains a
min/max pattern, and is nicely vectorized:
%11 = load i16, i16* %pSrcA.addr.010, align 2, !tbaa !3
%conv = sext i16 %11 to i32
%12 = load i16, i16* %pSrcB.addr.08, align 2, !tbaa !3
%conv2 = sext i16 %12 to i32
%mul = mul nsw i32 %conv2, %conv
%shr = ashr i32 %mul, 15
%13 = icmp slt i32 %shr, 32767
%spec.select.i = select i1 %13, i32 %shr, i32 32767
%conv3 = trunc i32 %spec.select.i to i16
store i16 %conv3, i16* %pDst.addr.09, align 2, !tbaa !3
Instead in the new has more expensive compare/select/trunc combo:
%11 = load i16, i16* %pSrcA.addr.010, align 2, !tbaa !3
%conv = sext i16 %11 to i32
%12 = load i16, i16* %pSrcB.addr.08, align 2, !tbaa !3
%conv2 = sext i16 %12 to i32
%mul = mul nsw i32 %conv2, %conv
%13 = lshr i32 %mul, 15
%cmp4.i = icmp sgt i32 %mul, 1073741823
%14 = trunc i32 %13 to i16
%conv3 = select i1 %cmp4.i, i16 32767, i16 %14
store i16 %conv3, i16* %pDst.addr.09, align 2, !tbaa !3
It appears that the function is differently optimized before it gets inlined?
It might also be possibly be fixed with a canonicalization fold:
https://alive2.llvm.org/ce/z/CwJcsD
We seem to have a lot of regressions in other suites which may be more
difficult to reproduce for upstream, due to the nature of the benchmarks. We
will see what we can do.
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